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Esta tesis doctoral fue leída en la Sala de Grados del edificio de Biología de la Universidad Autónoma de Madrid (UAM)., [EN] Evolutionary pressures linked to individual fitness drive the development and diversification of animal behaviour by favouring or punishing certain traits in the long-term. At the same time, individual behaviour can affect fitness if certain phenotypes are advantageous in terms of reproductive output or survival. This thesis aims to identify mechanisms that contribute to developing multiple behaviours in animals, as well as explore the potential role of behaviour as a driver of specialization. To do this, we studied behavioural traits (aggressiveness, exploration behaviour and foraging) in populations of a common forest passerine: the blue tit (Cyanistes caeruleus). We monitored these populations to understand parameters related to individual fitness regarding reproduction and survival. Reproduction success in birds is commonly assessed through parameters such as offspring condition, number of fledglings produced (total or relative to the clutch size), offspring recruitment rate… Survival information can be obtained through capture-recapture methods, which in birds often relies on the ringing of individuals and a maintained recapture effort. I present this thesis as a compendium of research articles that address the relationship between animal behaviour and fitness from different perspectives. The first article (section III) explores multiple aspects of male-male aggressive behaviour. Territorial males not only face the direct risks associated to conspecific aggressiveness (injuries or death). This behaviour also entails an investment of time and resources that is subtracted from other activities (i.e. courtship, nestbuilding, mate-care…). For our study population, we were able to define three strategies of territory defence with different associated risks: one confrontational and two nonconfrontational. The confrontational strategy relied heavily on direct attacks towards conspecific individuals. This strategy was displayed significantly more often by smaller and/or heavier males. The two non-confrontational strategies differed from each other: An intimidatory display relied on close proximity, aggressive flights and nest-signalling (perching more often and longer on the nest-box) to conspecifics, while a cautious strategy increased the visibility of the performing male (increased movements and vocalizations). We found that yearling males displayed intimidatory strategies more often than older males, which performed cautious displays significantly more often. In this study, we also provide results on how territory quality or habitat structure can contribute to modulating the type of aggressive strategy displayed. The second article (section IV) included in this thesis describes intersexual differences found in the studied population regarding exploration behaviour, and the potential mechanisms driving this process. Males in the study area have proven to be slower explorers than females. This result is particularly interesting because 1) the differences between sexes suggest that evolutionary pressures act unequally across sexes for exploration behaviour, and 2) an unbalance in selective pressures exists that erodes the faster-exploring phenotypes of males. In this article, we explored potential selective pressures that could favour slower-exploring males over faster-exploring ones. By analysing potential differences in reproductive and survival parameters, we found that nests with slow males had significantly shorter incubation periods. This could indicate that slowerexploring males are more attentive than faster ones, and could imply that this trait is being evolutionary selected for in our study population. Lastly, the third article (section V) presented in this thesis explores the potential role of exploration behaviour as a driver of individual diet specialization. Exploration behaviour may link to foraging activity through multiple mechanisms. For example, fast-exploring individuals may rely on easily-detectable (but smaller) prey, such as tortricid caterpillars, while slow-exploring ones may be more thorough foragers, obtaining more frequently bigger (but cryptic) prey, such as noctuid or geometrid caterpillars. By assessing the exploration behaviour and recording the provisioning activity, we were able to explore the relationship between these variables. Our results reveal that prey selection in the case of females not only depends on their exploration behaviour, but also relies on male provisioning activity. Furthermore, a trend suggests that fasterexploring males obtain marginally larger caterpillars, but provision less frequently, than slowerexploring males. As a conclusion, evolutionary pressures affecting the behaviour of blue tits in our study area act unequally across sexes, magnifying intersexual behavioural differences between males and females. Overall, less confrontational and slower-exploring males are favoured in our study area. It has been observed that individuals with “slower” bheavioural traits tend to be more adaptable than “faster” ones. Therefore, our results could indicate that the selection of slow traits is potentially a consequence of a changing environment. Future research should aim to widen the scale of the presented studies and explore the possibility that specific behavioural phenotypes may be selected under the current scenario of climate change., [ES] Las presiones evolutivas ligadas a la eficacia biológica (fitness) individual conducen al desarrollo y a la diversificación del comportamiento animal favoreciendo o penalizando ciertos rasgos. A su vez, el compotamiento individual puede afectar a la eficacia biológica si ciertos fenotipos tienen ventaja sobre otros en términos de reproducción o supervivencia. Esta tesis tiene como objetivo explorar, por un lado, los mecanismos que contribuyen al desarrollo de fenotipos comportamentales en animales y, por otro, el papel del comportamiento como promotor de procesos de especialización. Para ello, estudiamos determinados rasgos comportamentales (agresividad y comportamiento exploratorio) en poblaciones de un paseriforme común forestal, el herrerillo común (Cyanistes caeruleus). Monitoreamos estas poblaciones para obtener parámetros de eficacia biológica a nivel individual relacionados con reproducción y de supervivencia. El éxito reproductor en aves se mide a menudo a través de parámetros como la condición de los pollos, el número de pollos volados (total o relativo al tamaño de puesta), el reclutamiento de descendencia… La información relativa a la supervivencia individual puede obtenerse a través de métodos de captura-recaptura, que en aves a menudo se basa en el anillamiento de individuos y en un esfuerzo constante de recaptura. Presento esta tesis como un compendio de artículos científicos que abordan la relación entre el comportamiento animal y la eficacia biológica desde distintas perspectivas. El primer artículo explora el comportamiento agresivo de los machos. Los machos territoriales de herrerillo no sólo se enfrentan al riesgo directo asociado con la agresividad conspecífica (heridas o muerte), sino que este comportamiento también conlleva una inversión de tiempo y recursos en detrimento de otras actividades (p. ej. cortejo, construcción del nido, cuidado de la pareja reproductora…). Para nuestra población de estudio pudimos definir tres tipos de estrategias de defensa del territorio con distintos riesgos asociados: una estrategia confrontacional y dos no-confrontacionales. La estrategia confrontacional consiste en ataques directos sobre conspecíficos, y se da signficativamente más frecuentemente en individuos de menor tamaño y/o mayor peso. Las dos estrategias noconfrontacionales difieren: La estrategia intimidatoria se basa en vuelos agresivos, en aproximaciones y señalizaciones del nido (posándose más amenudo y más tiempo sobre la caja-nido) al conspecífico, mientras que machos con una estrategia precavida aumentan su visibilidad (mayor número de movimientos y vocalizaciones). Descubrimos que los machos jóvenes (de un año de edad) mostraban estrategias intimidatorias más a menudo que los machos mayores de un año, los cuales mostraron estrategias precavidas significativamente más a menudo que los jóvenes. Este estudio además proporciona resultados sobre cómo la calidad del territorio y la estructura del hábitat pueden contribuir a modular el tipo de estrategia agresiva. El segundo artículo (sección IV) incluido en esta tesis describe las diferencias intersexuales encontradas en el área de estudio relativas al comportamiento exploratorio y a los mecanismos potencialmente determinantes de este proceso. Los machos del área de estudio son exploradores más lentos que las hembras. Esto es particularmente interesante porque 1) esta diferencia intersexual sugiere que las presiones evolutivas actúan de manera diferente para los distintos sexos y 2) debe existir una falta de equilibrio en las presiones selectivas que erosiona los fenotipos de exploración rápida en los machos. En este artículo exploramos mecanismos que podrían favorecer a los machos lentos sobre los rápidos. Analizando posibles diferencias entre los parámetros reproductivos y de supervivencia observamos que los nidos con machos lentos tuvieron periodos de incubación significativamente menores. Esto podría indicar que los machos que exploran más despacio son generalmente más atentos con su pareja reproductora que los que exploran rápido, y este rasgo se está viendo favorecido evolutivamente en nuestra población de estudio. Por último, el tercer artículo (sección V) presentado en esta tesis explora la posibilidad de que el comportamiento exploratorio pueda generar una especialización en la dieta a nivel de individuo. El comportamiento exploratorio puede relacionarse con la búsqueda de alimento a través de diversos mecanismos. Por ejemplo, es posible que individuos que exploran más rápido dependan en mayor medida de presas más fácilmente detectables (pero más pequeñas), como las orugas de tortrícidos, mientras que los individuos que exploran más despacio pueden ser más rigurosos, obteniendo orugas más grandes (pero crípticas), como las de noctúido o geométrido. Evaluando el comportamiento exploratorio y grabando la actividad de aprovisionamiento en los nidos pudimos explorar la relación entre estas variables. Nuestros resultados revelan que la selección de presas, en el caso de las hembras, no dependió sólo de su comportamiento exploratorio, sino que también se relacionó con la frecuencia de aprovisionamiento de los machos. Además, parece que existe una tendencia que indica que los machos que exploran más rápido obtienen orugas marginalmente mayores en tamaño, pero alimentan a sus crías con menos frecuencia que los machos más lentos. Como conclusión, las presiones evolutivas están afectando a los herrerillos de nuestra área de trabajo de manera distinta entre sexos, magnificando las diferencias intersexuales comportamentales. En general, machos menos agresivos y que exploran más despacio están siendo favorecidos en estas poblaciones. Ha sido observado que individuos con rasgos comportamentales más “lentos” tienden a ser más adaptables que los individuos de rasgos “rápidos”. Por ello, nuestros resultados sugieren que la selección de estos rasgos “lentos” en nuestra población podrían ser consecuencia de una exposición a un ambiente cambiante. Las investigaciones futuras deberían tener como objetivo ampliar la escala de los estudios aquí presentados y explorar la posibilidad de que fenotipos comportamentales específicos sean seleccionados bajo las circunstancias actuales de cambio climático.

The Major Histocompatibility Complex (MHC) is a group of closely linked loci that play an important role in the immune system within all jawed vertebrates, and it has been shown to yield a higher fitness with an intermediate diversity. Several studies present how females choose their mates based on the MHC variability, hereby providing their offspring with the optimal variability. MHC class I (MHCI) mediates immunity against intracellular pathogens such as Haemoproteus, Plasmodium and Leucocytozoon. Here I investigate the MHCI composition in a population of blue tits (Cyanistes caeruleus) sampled in 2001 and 2021, and test whether social pairing departs from what is expected from random pairings. I also investigate the connection between the MHCI morphology, age and reproductive success. Additionally, I investigate the correlation between the MHCI and prevalence of the blood parasites Haemoproteus, Plasmodium and Leucocytozoon, and the correlation between these blood parasites, morphology, age and reproductive success. The younger females tended to be in social pairs with fewer positively selected site (PSS) alleles than expected from random pairings, whereas the older females tended to be in social pairs with more PSS alleles than expected. A higher number of MHCI alleles was linked to longer wings. Interestingly, there was an association between the number of MHCI alleles and Haemoproteus infection within the 2001 blue tits, with individuals with a higher number of alleles being more likely to be infected. Finally, a close to significant positive association was also found between the MHCI PSS allele IWYWYVGR and Haemoproteus infection. My results are most consistent with selection for a higher or lower number of alleles rather than an intermediate optimum, but additional studies are needed to further investigate these results.

**Abstract** Acoustic and visual signals are well known to play important roles in social communication in birds. Growing evidence suggests that many bird species, including species of songbirds, additionally have a well-developed sense of smell. However, we are still at the beginning of understanding the potential importance of chemical communication in the social lives of birds, for example in mate choice. The secretion of the preen gland may be an important contributor to the chemical phenotype of birds. Here, we report on a first characterisation of the chemical composition of the preen gland secretion of the Blue Tit (Cyanistes caeruleus), a common songbird which is an often used model species in animal behaviour and ecology, in particular also in studies of sexual selection and (extra-pair) mate choice. We found sex differences in the composition of the preen gland secretion in breeding Blue Tits. Females further tended to have a larger number of putative compounds in their secretions compared to males. We briefly discuss the possible implications of these findings and speculate that the chemical composition of the preen gland secretion may be a sexually selected trait in Blue Tits. Our preliminary findings warrant follow-up research into the patterns of within- and among individual variation in the chemical composition of the preen gland secretion as well as the identification of the main chemical compounds involved., **Zusammenfassung**Chemische Analyse zeigt Geschlechtsunterschiede im Bürzeldrüsensekret brütender BlaumeisenSingvögel sind vor allem für ihren Gesang und ihre Gefiedermerkmale, die bei der sozialen Kommunikation eine bedeutende Rolle spielen, bekannt. Immer mehr Hinweise deuten aber darauf hin, dass viele Vogelarten, darunter auch Singvogelarten, zusätzlich einen gut entwickelten Geruchssinn haben. Welche Bedeutung die geruchliche Kommunikation im sozialen Leben der Vögel, zum Beispiel bei der Partnerwahl, spielt ist allerdings weitgehend noch unbekannt. Das Bürzeldrüsensekret könnte in diesem Zusammenhang einen wichtigen Beitrag zum chemischen Phänotyp der Vögel leisten. In unserer Studie haben wir uns die chemische Zusammensetzung des Bürzeldrüsensekrets der Blaumeise (Cyanistes caeruleus) in der Brutzeit angeschaut. Blaumeisen sind eine viel genutzte Modellart in der Verhaltensforschung und Verhaltensökologie, insbesondere auch in Studien zur sexuellen Selektion und (außerpaarigen) Partnerwahl. Anhand von chemischen Analysen mittels Gas-Chromatographie fanden wir heraus, dass es bei brütenden Blaumeisen einen Geschlechtsunterschied in der Zusammensetzung des Bürzeldrüsensekrets gibt. Weibchen neigen außerdem dazu, eine größere Anzahl von vermeintlichen Substanzen in ihren Sekreten zu haben als Männchen. Wir diskutieren hier kurz die möglichen Implikationen dieser Ergebnisse und spekulieren, dass die chemische Zusammensetzung des Bürzeldrüsensekrets ein sexuell selektiertes Merkmal bei Blaumeisen sein könnte. Unsere vorläufigen Ergebnisse rechtfertigen Folgeuntersuchungen, in denen die Identifikation der wichtigsten chemischen Verbindungen des Bürzeldrüsensekrets und die Variation innerhalb und zwischen Individuen in der chemischen Zusammensetzung des Drüsensekrets im Fokus stehen.

A considerable number of avian species tend to use bryophytes as nest construction material, but the selectivity of birds in their bryophyte use in nest construction in relation to the availability of particular mosses in individual territories remains largely unexplored. We studied the bryophyte composition of nests in two passerine species: the Blue Tit Cyanistes caeruleus and the Great Tit Parus major in two floristically and structurally contrasting study areas (a mature deciduous forest and an urban parkland). We also studied territories within a radius of 10 m from each occupied nest box, listing all bryophyte species and checking to what extent the moss composition of the nest reflected what was available in the surrounding of the nest box. Both tit species appeared to be selective. The tits used a total of 31 bryophyte species in their nests (27 found in Blue Tits and 19 in Great Tits), whereas 25 additional bryophyte species were found around (10 m radius) the studied nests, but not in the nests. The number of bryophyte species found in individual nests varied in the urban parkland between 1 and 6 and in the forest between 1 and 11. The average number of bryophytes in the nest ranged from 2.31 in Great Tit from the urban parkland to 3.52 in Blue Tit in the urban parkland. Only a few species were used in a higher proportion than 5% of the volume within a single nest and, considering only these most abundant bryophyte species, the mean number ranged from 1.28 in Great Tits in the forest to 1.57 in Blue Tits in the urban parkland. Our study also showed that, in general, the bryophyte species composition of the nests seems to be affected by the site (the urban park vs the forest) rather than the parid species (Blue Tit vs Great Tit).

Evolutionary selection pressures, and species-specific ecology and behavior, promote a great variability in the size and composition of nests. However, it would be expected that phylogenetically close species, with similar ecological needs, breeding at the same time in the same place, would also build similar nests. In contrast with this, previous studies have found differences in nest mass and composition among closely related sympatric species. These differences have been attributed to small differences in body size (smaller species building larger and/or more insulated nests), or to the different ways in which species perceive the environment (e.g. perceived predation risk). In this study, for the first time, we searched for differences between nest mass, composition, and importance of the different functional parts of the nest between Blue (Cyanistes caeruleus), Great (Parus major) and Coal tits (Periparus ater) breeding under the same conditions. We found that smaller species built larger nests and/or include more thermoregulatory materials, probably having greater insulating capacity, which agrees with previous hypotheses. In particular, Blue Tits made greater use of bark, feathers and vegetable fiber, while Great Tits used wild boar hair in greater proportions. In addition, for the first time, we described in detail the nest composition of Coal Tits, which contained large amounts of fluff compared to the other two species. All these results are in line with previous hypothesis linking nest size and composition to the size of the birds, and the existence of species-specific characteristics in the selection of materials for nest building., This study was supported by projects CGL2013-48001-C2-1-P and CGL2016-79568-C3-1-P (Spanish Ministry of Economy and Competitiveness, MINECO). DD-M benefitted from an FPI fellowship (BES-2014-069191) provided by the MINECO, and was supported by the grant BABE 352805189 (European Research Council) during the last stages of the project.

Sexual conflict over parental investment in offspring occurs in species with biparental care due to the shared benefits but individual costs of care, such that the optimum level of investment for an individual is less than that of its partner. Sexual conflict can result in costs for offspring, but a recent theoretical model suggests that parents might reduce such costs via conditional cooperation in the form of turn-taking (alternation) during provisioning. Various empirical studies have found evidence supporting this model. In addition, provisioning synchrony is thought to be related to alternation, perhaps facilitating alternation by enabling partner monitoring. Whether these behaviours are adaptive is not yet fully understood, with studies calling for more research into the fitness consequences of these behaviours. As a result, this thesis explored potential costs and benefits for alternation and synchrony in blue tits, Cyanistes caeruleus, using 6 years of breeding and provisioning data. This study is the first to find evidence for benefits of alternation, finding that alternation predicts indicators of reproductive success. In addition, alternation was found to be predicted by brood size. Finally, this study found evidence for sex-specific costs of alternation, finding increased mortality in females that showed high alternation, while this trend did not occur males. These results provide novel insights into the costs and benefits of alternation, an important step in understanding whether this behaviour is adaptive.

Mycoplasma spp. are important pathogens in poultry and cause high economic losses for poultry industry worldwide. In other bird species (e.g. white storks, birds of prey, and several waterfowl species), Mycoplasma spp. are regularly found in healthy individuals, hence, considered apathogenic or part of the microbiota of the upper respiratory tract. However, as Mycoplasma spp. are absent in healthy individuals of some wild bird species, they might play a role as respiratory pathogen in these bird species, e.g. Mycoplasma gallisepticum in house finches. The knowledge on the occurrence of Mycoplasma spp. in wild birds is limited. To evaluate the relevance of Mycoplasma spp. in free-ranging nightingales and tits, 172 wild caught birds were screened for the presence of mycoplasmas. The birds were sampled via choanal swabs and examined via molecular methods (n = 172) and, when possible, via culture (n = 142). The Mycoplasma sp. was determined by sequencing the 16S rRNA gene and 16S-23S Intergenic Transcribed Spacer Region. All birds were tested negative for mycoplasmas via PCR and/or mycoplasmal culture. Hence, free-ranging nightingales and tits do not show any mycoplasma in their microbial flora of the respiratory tract. Therefore, these songbird species may suffer from clinical mycoplasmosis when being infected. We hypothesize that birds relying on their vocal ability for reproduction have excluded mycoplasmas from their respiratory flora compared to other bird species.

Microbiome constitutes an important axis of individual variation that, together with genes and the environment, influences an individual's physiology and fitness. Microbiomes are dependent not only on an individual's body condition but also on external factors, such as diet or stress levels, and as such can be involved into feedbacks between the external ecological factors and internal physiology. In our study, we used a wild population of blue tits Cyanistes caeruleus to investigate the impact of external habitat composition on the microbiome of adult birds. We hypothesized that - through differences in plant composition, potentially affecting diet complexity - habitat type may impact the diversity and structure of the gut microbiome. Blue tits breeding in dense deciduous forests tended to have more diverse microbiomes and be significantly different in terms of microbiome composition from birds breeding in open, sparsely forested hay meadows. Distinct study plots also tended to differ in a number of parameters describing microbiome diversity. We observed no microbiome differentiation according to individual characteristics such as sex or age. The study emphasizes that external environment is one of the important modulators of microbiome diversity and calls for more such studies in wild animal populations.

The following work contains an analysis of behavioural responses of Eurasian blue tits (Cyanistes caeruleus) and Great tits (Parus major) to heterospecific and conspecific alarm calls of Eurasian blue tit, Great tit, and alopatric Black-capped Chickadee (Poecile atricapillus) and Varied Tit (Sittiparus varius). Song of Eurasian blackcap (Sylvia atricapilla) was used as a baseline stimulus. I recorded and analyzed the following types of behaviour: the presence in the nearby surrondings of the nestbox, alarm calling, song and other calls.

Aposematic organisms warn predators of their unprofitability using a combination of defenses, including visual warning signals, startling sounds, noxious odors, or aversive tastes. Using multiple lines of defense can help prey avoid predators by stimulating multiple senses and/or by acting at different stages of predation. We tested the efficacy of three lines of defense (color, smell, taste) during the predation sequence of aposematic wood tiger moths (Arctia plantaginis) using blue tit (Cyanistes caeruleus) predators. Moths with two hindwing phenotypes (genotypes: WW/Wy = white, yy = yellow) were manipulated to have defense fluid with aversive smell (methoxypyrazines), body tissues with aversive taste (pyrrolizidine alkaloids) or both. In early predation stages, moth color and smell had additive effects on bird approach latency and dropping the prey, with the strongest effect for moths of the white morph with defense fluids. Pyrrolizidine alkaloid sequestration was detrimental in early attack stages, suggesting a trade-off between pyrrolizidine alkaloid sequestration and investment in other defenses. In addition, pyrrolizidine alkaloid taste alone did not deter bird predators. Birds could only effectively discriminate toxic moths from non-toxic moths when neck fluids containing methoxypyrazines were present, at which point they abandoned attack at the consumption stage. As a result, moths of the white morph with an aversive methoxypyrazine smell and moths in the treatment with both chemical defenses had the greatest chance of survival. We suggest that methoxypyrazines act as context setting signals for warning colors and as attention alerting or “go-slow” signals for distasteful toxins, thereby mediating the relationship between warning signal and toxicity. Furthermore, we found that moths that were heterozygous for hindwing coloration had more effective defense fluids compared to other genotypes in terms of delaying approach and reducing the latency to drop the moth, suggesting a genetic link between coloration and defense that could help to explain the color polymorphism. Conclusively, these results indicate that color, smell, and taste constitute a multimodal warning signal that impedes predator attack and improves prey survival. This work highlights the importance of understanding the separate roles of color, smell and taste through the predation sequence and also within-species variation in chemical defenses.

Las cajas-nido constituyen una herramienta muy útil para el desarrollo de diversos estudios en aves, pues permiten el diseño experimental y la comparación de muestras sometidas a distintos tratamientos o localizaciones. Igualmente, son útiles para la conservación de aves en hábitats con muy poco arbolado maduro, como ocurre en muchos parques urbanos. Con el fin de impulsar la biodiversidad en el ámbito urbano, la Sociedad de Ciencias Aranzadi inició en 2018 el proyecto Hirilife, entre cuyas acciones estaba la colocación de cajas nido para aves paseriformes insectívoras en arbolado en calles, paseos y parques urbanos de la ciudad de San Sebastián. Este artículo se presenta con el fin de (1) determinar la tasa de ocupación de estas cajas-nido; y (2) explorar los factores que condicionan esta ocupación, con el fin de establecer, a futuro, una guía de buenas prácticas orientada a optimizar su colocación. A lo largo de la primavera de 2020 se revisaron 202 cajas en total, de las 220 que se habían colocado. Se ocuparon un total de 91 (45%). La tasa de ocupación, no obstante, varió significativamente entre zonas. Las cajas en las que se pudo determinar la especie fueron ocupadas por dos especies de páridos: el herrerillo común Cyanistes caeruleus y el carbonero común Parus major. Se observa una dominancia del carbonero común (31 versus 10 cajas; el resto se corresponde con las que no se pudo determinar la especie). Según los modelos las cajas son ocupadas con más probabilidad cuando se sitúan en entornos con una gran cantidad de hábitat natural. Abstract: Nest-boxes constitute a very useful tool in ornithological studies, since they allow the development of experimental designs and permit comparisons to be made between samples subjected to different treatments and locations. Moreover, they are also useful for bird conservation in habitats with low amounts of mature trees, as occurs in many urban parks. The ‘Hirilife’ project, developed by the Aranzadi Sciences Society, was launched in 2018 with the aim of promoting biodiversity in urban areas. This project included actions oriented to install and monitor nest-boxes for insectivorous passerine birds in the streets, promenades and parks of the city of San Sebastian. As a result, in this article we (1) describe the nest-box occupation rate, and (2) examine those factors that determine this rate, with the aim of drawing up a good practice guide to optimize the installation of new nestboxes in the future. During the spring of 2020, 202 nest-boxes were surveyed. Overall, 91 were occupied (45%). The occupation rate, however, varied substantially between zones. The nest-boxes were occupied by two species: the blue tit Cyanistes caeruleus and the great tit Parus major. The latter species was dominant (31 versus 10 nest-boxes). According to the model of nest-box, these were more likely to be occupied when they were situated in areas close to/surrounded by a high amount of natural habitat.

Funding: Japan Society for the Promotion of Science (Grant Number(s): H28/1018); Biotechnology and Biological Sciences Research Council (Grant Number(s): BB/S01019X/1, EASTBIO scholarship). The materials that birds use to build their nests have a profound effect on nest quality and consequently on the builder’s reproductive success. Given that the common method to quantify nest materials by dismantling nests takes time and limits study species, we developed a non‐destructive and much quicker method for quantifying nest materials using nest photographs. Using our photographic method, the proportions of the main materials in 45 Blue Tit Cyanistes caeruleus and 20 Dartford Warbler Sylvia undata nests, including grass, heather, and moss, matched those found by dismantling the nests, while the proportions of rarer animal‐derived materials differed between the two methods. Provided that there is an initial calibration with the dismantling method, the photographic method offers the two key advantages: the reduction in time it takes to quantify the major components of nests, and the application to previously inaccessible data including museum collections. Together, these advantages encourage further study of nesting materials and enable a better understanding of avian nest diversification. Publisher PDF

Climate warming affects trophic interactions in ecosystems, which has been documented for relationships between plants, herbivores and predators, including their relative densities, varying between taxons/guilds. In the case of leaf-eating caterpillars feeding in tree canopies the use of caterpillar frass fall as an indicator of density and production has proven to be advisable. Here we analysed annual variation in the peak mass of caterpillar frass fall and the timing of the occurrence of the peak mass in a deciduous forest site as compared with an urban park site during 16 consecutive years (2003–2018) in central Poland. Variation in the mean date of the frass fall peak mass among years was extensive, up to 20 days, with the sequence of the occurrence in the study habitats differing between years. There was a significant advance in the date of the peak frass fall in the course of the study years. There was also great variation in the peak frass fall mass between years and study sites. The tree canopy caterpillars were consistently less numerous in the urban park than in the deciduous forest. Cyclical outbreaks of caterpillars, whose signs were visible in the data set, possibly tended to decline. A decline in the annual peak mass of frass fall over the study period was found. No evidence for synchronization of the timing of blue tit Cyanistes caeruleus breeding with the timing of peak caterpillar abundance was found. The annual average peak mass of caterpillar frass fall proved to be a significant predictor of the annual mean number of fledgling blue tits per brood. Both the consistent pattern of spatio-temporal variation in the timing of peak availability and the abundance of tree-canopy caterpillars and the effects of caterpillar abundance on an insectivorous bird confirm that frass fall is a useful indicator of tri-trophic links to birds that prey upon caterpillars.

Social learning in animals is a frequently studied topic, including birds. Great tits belong to frequently tested passerine species in this context. For this experiment we have chosen another tit species as model birds - adult and juvenile blue tits (Cyanistes caeruleus) and coal tits (Periparus ater). We tested an effect of social information on discrimination learning between palatable and unpalatable prey. Red and green artificial prey items resembling shieldbugs with a mealworm glued underneath were offered to birds. One variant was palatable, the other was unpalatable, soaked in bitter substance. Experimental groups were allowed to observe a pretrained tutor of the same species choosing palatable prey variant and rejecting the unpalatable one. The birds were then subjected to an individual discrimination learning task with simultaneously offered palatable and unpalatable prey items. The control group was not allowed to observe tutor and learned only individually. On the following day, all birds participated in a memory test. We tested if social information has an influence on avoidance learning in juvenile and adult birds of both species. We found that both species of tits were similarly successful in discrimination learning and there was no difference in success in performance between adult...

Saalistajien torjumiseksi saalis voi käyttää erilaisia puolustusmekanismeja, jotka stimuloivat useita eri aisteja (ts. multimodaalista signalointia). Esimerkiksi aposemaattiset eliöt puolustautuvat varoitussignaalin lisäksi sekundaarisella puolustuksella. Tässä tutkimuksessa keskityttiin siihen, kuinka täpläsiilikkään (Arctia plantaginis) väritys (genotyypit WW, Wy ovat valkoisia ja yy keltaisia), haju (metoksipyratsiinista) ja maku (pyrrolitsidiinialkaloidista) toimivat puolustuksena lintusaalistajien hyökkäyksiä vastaan. Linnuille tarjottiin kummankin värisiä eläviä siilikkäitä, joita oli manipuloitu niin, että niillä oli joko hajua, makua tai molempia näistä. Näin pystyttiin tutkimaan kuinka väritys, haju ja maku vuorovaikuttavat saalistustapahtumassa. Linnut lähestyivät hitaimmin valkoisia siilikkäitä, joilla oli pahaa hajua, ja myös pudottivat niitä useimmin. Maku yksinään ei torjunut lintuja, ja linnut söivät siilikkäästä vähemmän vain silloin, kun hajua esiintyi maun kanssa. Parhaimmat mahdollisuudet selvitä hengissä oli valkoisilla siilikkäillä, joilla oli sekä pahaa hajua että makua. Kun valkoisten siilikkäiden puolustustehokkuutta tutkittiin tarkemmin, heterotsygoottisten siilikkäiden hajun havaittiin olevan tehokkainta lähestymisajan pidentämiseen ja saaliin nopeampaan pudottamiseen, mikä voi auttaa selittämään tämän lajin polymorfismia. Nämä tulokset osoittavat, että multimodaalisuus parantaa saaliin selviytymistä saalistajaa vastaan suojaamalla saalista koko hyökkäyksen ajan. Julkaistu artikkeli: Front. Ecol. Evol., 16 August 2021, https://doi.org/10.3389/fevo.2021.657740 To ward off predators prey may use defences that stimulate multiple sensory modalities (i.e., multimodal signalling). For example aposematic organisms are defended against predators with a warning signal combined with a secondary defence. This study focused on how the wood tiger moth (Arctia plantaginis) colour (genotypes WW and Wy are white and yy is yellow), smell (from methoxypyrazines) and taste (from pyrrolizidine alkaloids) deter bird predators. Live moths of both colours, that were manipulated to have each chemical defence alone or in combination, were offered to birds to test how visual warning signals, smell and taste, interact through the predation event. White coloured moths with methoxypyrazine smell had the strongest effect on delaying the approach latency and increasing the number of times the bird dropped the moth. Taste alone did not deter birds and birds reduced the amount eaten only when smell was present in combination with taste. Overall, moths that had white hindwings, and had both smell and bad taste, had the best chance of survival. When defence efficacy of the white moths was explored in closer detail, heterozygous moths were found to have the most effective neck fluids (smell) in terms of delaying approach latency and reducing the drop latency of predators, which can help to explain the polymorphism in this species. These results indicate that multimodality improves prey anti-predator defence by providing protection throughout the attack. Published article: Front. Ecol. Evol., 16 August 2021, https://doi.org/10.3389/fevo.2021.657740

Vision is a vital attribute to foraging, navigation, mate selection and social signalling in animals, which often have a very different colour perception in comparison to humans. For understanding how animal colour perception works, vision models provide the smallest colour difference that animals of a given species are assumed to detect. To determine the just-noticeable-difference, or JND, vision models use Weber fractions that set discrimination thresholds of a stimulus compared to its background. However, although vision models are widely used, they rely on assumptions of Weber fractions since the exact fractions are unknown for most species. Here, we test; i) which Weber fractions in long-, middle- and shortwave (i.e. L, M, S) colour channels best describe the blue tit (Cyanistes caeruleus) colour discrimination, ii) how changes in hue of saturated colours and iii) chromatic background noise impair search behaviour in blue tits. We show that the behaviourally verified Weber fractions on achromatic backgrounds were L: 0.05, M: 0.03 and S: 0.03, indicating a high colour sensitivity. In contrast, on saturated chromatic backgrounds, the correct Weber fractions were considerably higher for L: 0.20, M: 0.17 and S: 0.15, indicating a less detailed colour perception. Chromatic complexity of backgrounds affected the longwave channel, while middle- and shortwave channels were mostly unaffected. We caution that using a vision model whereby colour discrimination is determined in achromatic viewing conditions, as they often are, can lead to misleading interpretations of biological interactions in natural – colourful – environments. peerReviewed

International audience; Climate change is associated with advancing phenology of seasonal traits in many taxa, but shifts by higher trophic levels are generally reduced compared with those of lower trophic levels. For example, the eclosion date of caterpillars and the lay date of insectivorous passerine birds have both advanced recently, but the former has done so more than the latter. While the ensuring phenological mismatch between predator and prey is well-documented, our understanding of the origins of this mismatch is more limited. Here we shed light on the interplay between ambient temperature, breeding phenology and reproductive success in a single population of blue tits (Cyanistes caeruleus) nesting over a 1,000 m (∼5°C) elevational gradient in the French Pyrenees. During the 6 years of this study, we found that average breeding phenology varied by 2–9 days among years, but was on average 11 days earlier at low versus high elevation. Despite the delay, breeding at high elevation was associated with lower and more variable temperatures during breeding. Early breeders within a given year generally had larger clutch sizes than late breeders, which led to more offspring fledged as typically found in other studies. However, in three of the 6 years, the probability of producing fledglings was actually lower among early layers. Additionally, birds breeding at high elevations who experience conditions typical of early breeders in other populations had reduced hatching success and were significantly less likely to fledge any young compared with those breeding at lower elevation. Reduced success at high elevation was not obviously driven by higher nest predation, which was exceptionally low, or reduced food availability because high elevation birds laid clutches of comparable size and fledged the same number of offspring of comparable mass as those breeding at low elevation. Our study reveals the capacity for substantial variation in breeding phenology within a population, but that the success of early breeders varies across years and temperature gradients. We suggest that the evolution of phenological advancements by small endotherms might be curtailed by increased probability of experiencing, and failure under, challenging meteorological conditions in late winter or very early spring.

Aim: Nest building is widespread among animals. Nests may provide receptacles for eggs, developing offspring and the parents, and protect them from adverse environmental conditions. Nests may also indicate the quality of the territory and its owner and can be considered as an extended phenotype of its builder(s). Nests may, thus, function as a sexual and social signal. Here, we examined ecological and abiotic factors—temperature, nest predation and interspecific information utilization—shaping geographical variation in a specific nest structure—hair and feather cover of eggs—and its function as an extended phenotype before incubation in great (Parus major) and blue tits (Cyanistes caeruleus) across Europe. We also tested whether egg covering is associated with reproductive success of great tits. Location: Fourteen different study sites and 28 populations across Europe. Taxon: Parus major, Cyanistes caeruleus. Methods: We recorded clutch coverage estimates and collected egg covering nest material from the tit nests. We also measured nest specific breeding parameters and phenotypic measurements on adults. We tested whether mean spring temperatures, nest predation rates and flycatcher (Ficedula spp) densities in the study areas explain the large‐scale geographical variation of clutch coverage and reproductive success of tits. Results: The degree of egg coverage of great tits increased with lower mean spring temperature, higher nest predation rate and higher flycatcher density. We did not find egg covering of blue tits to be associated with any of the ecological or abiotic factors. Moreover, egg covering of great tits was not associated with reproductive success in our cross‐sectional data, yet a rigorous assessment of fitness effects would require long‐term data. Main conclusions: Our findings suggest that, in great tits, egg covering may simultaneously provide thermal insulation against cold temperatures during egg‐laying in spring and also represent a counter‐adaptation to reduce information parasitism by flycatchers and nest predation. Hence, geographical variation in interspecific interactions, and consequently in co‐evolutionary processes, may affect the evolution of nest characteristics besides environmental conditions.

Understanding the ecology and evolution of parasites is contingent on identifying the selection pressures they face across their infection landscape. Such a task is made challenging by the fact that these pressures will likely vary across time and space, as a result of seasonal and geographical differences in host susceptibility or transmission opportunities. Avian haemosporidian blood parasites are capable of infecting multiple co‐occurring hosts within their ranges, yet whether their distribution across time and space varies similarly in their different host species remains unclear. Here, we applied a new PCR method to detect avian haemosporidia (genera Haemoproteus, Leucocytozoon, and Plasmodium) and to determine parasite prevalence in two closely related and co‐occurring host species, blue tits (Cyanistes caeruleus, N = 529) and great tits (Parus major, N = 443). Our samples were collected between autumn and spring, along an elevational gradient in the French Pyrenees and over a three‐year period. Most parasites were found to infect both host species, and while these generalist parasites displayed similar elevational patterns of prevalence in the two host species, this was not always the case for seasonal prevalence patterns. For example, Leucocytozoon group A parasites showed inverse seasonal prevalence when comparing between the two host species, being highest in winter and spring in blue tits but higher in autumn in great tits. While Plasmodium relictum prevalence was overall lower in spring relative to winter or autumn in both species, spring prevalence was also lower in blue tits than in great tits. Together, these results reveal how generalist parasites can exhibit host‐specific epidemiology, which is likely to complicate predictions of host–parasite co‐evolution., Understanding the ecology and evolution of parasites is contingent on identifying the selection pressures they face across their infection landscape. Here, we detect avian haemosporidia (genera Haemoproteus, Leucocytozoon, and Plasmodium) and determine parasite prevalence in two closely related and co‐occurring host species, blue tits (Cyanistes caeruleus) and great tits (Parus major). We study changes in prevalence across an elevational gradient and between seasons. Our results reveal how generalist parasites can exhibit host‐specific epidemiology, which is likely to complicate predictions of host–parasite co‐evolution.

Small animals that winter at northern latitudes need to maximize energy intake and minimize energy loss. Many passerine birds use night-time hypothermia to conserve energy. A potential cost of night-time hypothermia with much theoretical (but little empirical) support is increased risk of night-time predation, due to reduced vigilance and lower escape speed in hypothermic birds. This idea has never been tested in the wild. We, therefore, increased perceived predation risk in great tits (Parus major) and blue tits (Cyanistes caeruleus) roosting in nest boxes during cold winter nights to measure any resultant effect on their use of night-time hypothermia. Roosting birds of both species that experienced their first winter were less prone to use hypothermia as an energy-saving strategy at low ambient temperatures when exposed to increased perceived predation risk either via handling (great tits) or via predator scent manipulation (blue tits). However, we did not record such effects in birds that were in their second winter or beyond. Our results suggest that effects of increased predation risk are age- and temperature specific. This could be caused by age-related differences in experience and subsequent risk assessment, or by dominance-related variation in habitat quality between young and old birds. Predation risk could, through its effect on use and depth of night-time hypothermia, be important for total energy management and winter survival for resident birds at northern latitudes.

Rather little is known about the dietary richness and variation of generalist insectivorous species, including birds, due primarily to difficulties in prey identification. Using faecal metabarcoding, we provide the most comprehensive analysis of a passerine's diet to date, identifying the relative magnitudes of biogeographic, habitat and temporal trends in the richness and turnover in diet of Cyanistes caeruleus (blue tit) along a 39 site and 2° latitudinal transect in Scotland. Faecal samples were collected in 2014-2015 from adult birds roosting in nestboxes prior to nest building. DNA was extracted from 793 samples and we amplified COI and 16S minibarcodes. We identified 432 molecular operational taxonomic units that correspond to putative dietary items. Most dietary items were rare, with Lepidoptera being the most abundant and taxon-rich prey order. Here, we present a statistical approach for estimation of gradients and intersample variation in taxonomic richness and turnover using a generalised linear mixed model. We discuss the merits of this approach over existing tools and present methods for model-based estimation of repeatability, taxon richness and Jaccard indices. We found that dietary richness increases significantly as spring advances, but changes little with elevation, latitude or local tree composition. In comparison, dietary composition exhibits significant turnover along temporal and spatial gradients and among sites. Our study shows the promise of faecal metabarcoding for inferring the macroecology of food webs, but we also highlight the challenge posed by contamination and make recommendations of laboratory and statistical practices to minimise its impact on inference.

Summary Offspring often solicit, and compete for, limited parental care by elaborate begging behaviour. Kin selection theory predicts that competing offspring should modify the intensity of their begging depending on the degree of relatedness to their nest- or litter-mates. Empirical evidence in birds, which are a key model in the study of parent-offspring interactions, indeed indicates that a lower level of relatedness between offspring in the nest correlates with more intense begging (i.e. more ‘selfish’ behaviour). This implies that competing nestlings can recognize kin, but the mechanism underlying such discrimination is unclear. Birds have long been thought to mainly rely on visual and auditory cues in their social communication, but there is now growing evidence for the importance of olfactory cues too. To assess the potential importance of olfactory cues in modulating nestling begging behaviour, we experimentally tested in a free-living bird, the blue tit Cyanistes caeruleus, if nestlings discriminate and adjust their begging behaviour depending on their familiarity with a conspecific nestling odour stimulus. We found that individuals responded with longer and more intense begging bouts to an unfamiliar compared with a familiar odour stimulus. Our findings provide first evidence for a role of olfaction in modulating offspring begging behaviour in a wild bird population. Although our experiment cannot differentiate between the effects of familiarity and relatedness, it raises the interesting possibility that blue tit nestlings may also discriminate between odours of close kin and less related individuals, and adjust their begging behaviour accordingly. This hypothesis requires further testing. A lay summary is available for this article.

The incubation stage in avian reproduction could be as costly as the nestling rearing stage. This is particularly true in the case of uniparental incubation, during which both current and future breeding attempts may be compromised. Therefore, the knowledge of the proximate effects that condition the incubation behaviour in free-living bird populations is of great importance in understanding the evolution of avian life history. In this two-year study, we assessed the incubation behaviours of Blue Cyanistes caeruleus and Great Tits Parus major inhabiting the same Mediterranean area in central Spain through the usage of iButton data loggers. It showed that the incubating behaviour of our tit populations resembles that reported in previous studies, but with peculiarities related to living at lower latitudes, i.e. with a relatively low attentiveness and a shorter active day. Both tit species showed very different incubation strategies, with Blue Tits leaving more frequently the nest (Mean ± SE number of off-bouts, Blue Tit = 27.14 ± 0.63, Great Tit = 16.95 ± 0.58) but for shorter periods than Great Tits (off-bout duration, Blue Tit = 8.76 ± 0.22 min, Great Tit = 14.04 ± 0.56 min; on-bout duration, Blue Tit = 22.63 ± 0.60 min, Great Tit = 36.86 ± 0.86 min). Nonetheless, both species provided a similar nest attentiveness, percentage of time of the active day during which the females were actively incubating (Blue Tit = 70.87 ± 0.57%, Great Tit = 70.75 ± 0.83%). Presumably, differences in the cooling rate of clutches, estimated with the iButtons, could be behind the differences in incubation behaviour between species and the greater capacity of Great Tits to adjust their incubation behaviour., Funding was provided by Ministerio de Economía y Competitividad (CLG2013-48001-C2-1P) and Junta de Comunidades de Castilla-La Mancha and European Social Fund (POIC10-0269- 7632). JBE is supported by a doctoral scholarship from the Junta de Comunidades de Castilla-La Mancha-European Social Fund and RB is a part of the JCCM-FSE 2007/2013 postdoctoral program and has a “Juan de la Cierva” post-doctoral contract (JCI-2011-10945).

Context Connectivity is fundamental to understanding how landscape form influences ecological function. However, uncertainties persist due to the difficulty and expense of gathering empirical data to drive or to validate connectivity models, especially in urban areas, where relationships are multifaceted and the habitat matrix cannot be considered to be binary. Objectives This research used circuit theory to model urban bird flows (i.e. ‘current’), and compared results to observed abundance. The aims were to explore the ability of this approach to predict wildlife flows and to test relationships between modelled connectivity and variation in abundance. Methods Circuitscape was used to model functional connectivity in Bedford, Luton/Dunstable, and Milton Keynes, UK, for great tits (Parus major) and blue tits (Cyanistes caeruleus), drawing parameters from published studies of woodland bird flows in urban environments. Model performance was then tested against observed abundance data. Results Modelled current showed a weak yet positive agreement with combined abundance for P. major and C. caeruleus. Weaker correlations were found for other woodland species, suggesting the approach may be expandable if re-parameterised. Conclusions Trees provide suitable habitat for urban woodland bird species, but their location in large, contiguous patches and corridors along barriers also facilitates connectivity networks throughout the urban matrix. Urban connectivity studies are well-served by the advantages of circuit theory approaches, and benefit from the empirical study of wildlife flows in these landscapes to parameterise this type of modelling more explicitly. Such results can prove informative and beneficial in designing urban green space and new developments.

Assortative mating is a potential outcome of sexual selection, and estimating its level is important to better understand local adaptation and underlying trait evolution. However, assortative mating studies frequently base their conclusions on small numbers of individuals sampled over short periods of time and limited spatial scales even though spatiotemporal variation is common. Here, we characterized assortative mating patterns over 10 years in four populations of the blue tit (Cyanistes caeruleus), a passerine bird. We focused on two plumage ornaments—the blue crown and the yellow breast patch. Based on data for 1,657 pairs of birds, we found large interannual variation: assortative mating varied from positive to negative. To determine whether there was nonetheless a general trend in the data, we ran a within‐study meta‐analysis. It revealed that assortative mating was moderately positive for both ornaments. It also showed that mating patterns differed among populations and especially between two neighboring populations that displayed phenotypic divergence. Our results therefore underscore that long‐term studies are needed to draw broad conclusions about mating patterns in natural populations. They also call for studying the potential role of assortative mating in local adaptation and evolution of ornaments in both sexes.

There is abundant evidence in many taxa for positive 2 directional selection on body size, and yet little evidence for microevolutionary change. In many species, variation in body size is partly determined by the actions of parents, so a proposed explanation for stasis is the presence of a negative genetic correlation between direct and parental effects. Consequently, selecting genes for increased body size would result in a correlated decline in parental effects, reducing body size in the following generation. We show that these arguments implicitly assume that parental care is cost free, and that including a cost alters the predicted genetic architectures needed to explain stasis. Using a large cross-fostered population of blue tits, we estimate direct selection on parental effects for body mass, and show it is negative. Negative selection is consistent with a cost to parental care, mainly acting through a reduction in current fecundity rather than survival. Under these conditions, evolutionary stasis is possible for moderately negative genetic correlations between direct and parental effects. This is in contrast to the implausibly extreme correlations needed when care is assumed to be cost free. Thus, we highlight the importance of accounting correctly for complete selection acting on traits across generations.

We studied the relationship between temperature and the coexistence of great titParus majorand blue titCyanistes caeruleus, breeding in 75 study plots across Europe and North Africa. We expected an advance in laying date and a reduction in clutch size during warmer springs as a general response to climate warming and a delay in laying date and a reduction in clutch size during warmer winters due to density-dependent effects. As expected, as spring temperature increases laying date advances and as winter temperature increases clutch size is reduced in both species. Density of great tit affected the relationship between winter temperature and laying date in great and blue tit. Specifically, as density of great tit increased and temperature in winter increased both species started to reproduce later. Density of blue tit affected the relationship between spring temperature and blue and great tit laying date. Thus, both species start to reproduce earlier with increasing spring temperature as density of blue tit increases, which was not an expected outcome, since we expected that increasing spring temperature should advance laying date, while increasing density should delay it cancelling each other out. Climate warming and its interaction with density affects clutch size of great tits but not of blue tits. As predicted, great tit clutch size is reduced more with density of blue tits as temperature in winter increases. The relationship between spring temperature and density on clutch size of great tits depends on whether the increase is in density of great tit or blue tit. Therefore, an increase in temperature negatively affected the coexistence of blue and great tits differently in both species. Thus, blue tit clutch size was unaffected by the interaction effect of density with temperature, while great tit clutch size was affected in multiple ways by these interactions terms. Institute of Biology of Karelian Research Centre 0218-2019-0080 Academy of Finland 265859 Ministerio de Economía y Competitividad CGL-2016-79568-C3-3-P

The plastic regulation of internal energy reserves is acknowledged as the main adaptive response to winter conditions of resident small birds in northern latitudes, a strategy that may be altered whenever human‐supplemented food is available. We investigated the effects of supplementary feeding on the energy management strategy of two wild passerine species, the Willow Tit Poecile montanus and Blue Tit Cyanistes caeruleus, wintering in boreal conditions by measuring body mass and the energy cost of living, i.e. basal metabolic rate. Individuals of both species were heavier, larger and exhibited a higher energy cost of living when captured at the feeders than were individuals captured away from feeders. Fed Willow Tits expended more energy in maintenance, although this difference disappeared once mass was accounted for. Conversely, Blue Tits at feeders had higher mass‐adjusted energy cost of living, but only at low ambient temperatures. The results indicate that winter feeding has species‐specific effects on overall energy management strategy and modifies the response to environmental conditions of wintering passerines.

We studied the relationship between temperature and the coexistence of great tit Parus major and blue tit Cyanistes caeruleus, breeding in 75 study plots across Europe and North Africa. We expected an advance in laying date and a reduction in clutch size during warmer springs as a general response to climate warming and a delay in laying date and a reduction in clutch size during warmer winters due to density-dependent effects. As expected, as spring temperature increases laying date advances and as winter temperature increases clutch size is reduced in both species. Density of great tit affected the relationship between winter temperature and laying date in great and blue tit. Specifically, as density of great tit increased and temperature in winter increased both species started to reproduce later. Density of blue tit affected the relationship between spring temperature and blue and great tit laying date. Thus, both species start to reproduce earlier with increasing spring temperature as density of blue tit increases, which was not an expected outcome, since we expected that increasing spring temperature should advance laying date, while increasing density should delay it cancelling each other out. Climate warming and its interaction with density affects clutch size of great tits but not of blue tits. As predicted, great tit clutch size is reduced more with density of blue tits as temperature in winter increases. The relationship between spring temperature and density on clutch size of great tits depends on whether the increase is in density of great tit or blue tit. Therefore, an increase in temperature negatively affected the coexistence of blue and great tits differently in both species. Thus, blue tit clutch size was unaffected by the interaction effect of density with temperature, while great tit clutch size was affected in multiple ways by these interactions terms. Institute of Biology of Karelian Research Centre 0218-2019-0080 Academy of Finland 265859 Ministerio de Economía y Competitividad CGL-2016-79568-C3-3-P

We studied the relationship between temperature and the coexistence of great tit Parus major and blue tit Cyanistes caeruleus, breeding in 75 study plots across Europe and North Africa. We expected an advance in laying date and a reduction in clutch size during warmer springs as a general response to climate warming and a delay in laying date and a reduction in clutch size during warmer winters due to density-dependent effects. As expected, as spring temperature increases laying date advances and as winter temperature increases clutch size is reduced in both species. Density of great tit affected the relationship between winter temperature and laying date in great and blue tit. Specifically, as density of great tit increased and temperature in winter increased both species started to reproduce later. Density of blue tit affected the relationship between spring temperature and blue and great tit laying date. Thus, both species start to reproduce earlier with increasing spring temperature as density of blue tit increases, which was not an expected outcome, since we expected that increasing spring temperature should advance laying date, while increasing density should delay it cancelling each other out. Climate warming and its interaction with density affects clutch size of great tits but not of blue tits. As predicted, great tit clutch size is reduced more with density of blue tits as temperature in winter increases. The relationship between spring temperature and density on clutch size of great tits depends on whether the increase is in density of great tit or blue tit. Therefore, an increase in temperature negatively affected the coexistence of blue and great tits differently in both species. Thus, blue tit clutch size was unaffected by the interaction effect of density with temperature, while great tit clutch size was affected in multiple ways by these interactions terms., A. Artemyev acknowledges funding by IB KRC RAS no. 0218-2019-0080 and T. Eeva acknowledges funding by the Academy of Finland (project 265859). This study was funded by research project CGL-2016-79568-C3-3-P (to J. C. Senar), from the Ministry of Economy and Competitivity, Spanish Research Council.

Animals constantly need to relate to prevailing environmental conditions and regulate their body temperature accordingly. Body temperature regulation in birds and mammals is inherently linked to energy expenditure and, thus, thermoregulation is a physiological mechanism that could trade-off with other costly processes, with potential long-term fitness consequences. In this thesis, I studied ecological and physiological sources of variation in body temperature across age and seasons, and how variation in thermoregulatory patterns trade-off with other processes within a life-history framework. More specifically, I studied how thermoregulatory development was affected by early life thermal environment and how body temperature was regulated and maintained outside of thermoneutrality. For this purpose, I used small, hole-nesting, passerine birds both during the nestling stage and as adult birds in winter and during breeding.I found that nest environment affected body temperature regulation, short-term growth and development in nestlings but that there also might be long-term effects on apparent survival. More specifically, growing up in a small brood allowed for investment in both growth and thermoregulatory development, compared to nestlings that grew up in large broods. By experimentally increasing nest temperature I was also able to show that nestlings were well equipped to deal with increased nest temperatures, but that it came with a cost in lower body mass gain, and that increased nest temperatures could potentially have positive effects on long-term survival. While working hard to feed their young, the risk of overheating can constrain parental work rate. By experimentally reducing this constraint, I found that females were able to increase innate immune function while reducing work rate, but without compromising nestling development. In winter, small passerines routinely reduce body temperature during the night, thereby lowering energy expenditure. I found that young birds (in their first winter) had both higher metabolic rate and body temperature during the night compared to old birds (in their second winter or older). Such differences could be related to experience-based variation in assessment of predation risk or age-related differences in plumage quality. I also show that handling birds in winter caused a pronounced decrease in body temperature, highlighting the importance of plumage in maintaining body temperature in the cold for these small birds. Overall, these studies demonstrate the need for including age-effects into studies of thermoregulation and energy management in the cold. I have, for the most part, studied avian thermoregulation outside of thermoneutrality, when additional energy is required to maintain body temperature. Given the current changes to our climate, with an expected increased frequency of extreme weather, studies like these can add important knowledge to our understanding of how animals respond physiologically to such changes and how this, potentially, could shape life-histories.

In bi-parental systems each parent shares benefits with its unrelated partner from the common investment in offspring, but pays an individual cost of providing that care in terms of reduced survival or fecundity, leading to sexual conflict. However, several recent empirical studies have shown that coordinating behaviours like synchronisation (e.g. arriving at similar times) and alternation (taking turns in providing care) at the nest lead to increased investment overall, presumably to reduce conflict through policing or synergistic benefits. Ecological conditions should impact the costs and benefits of bi-parental care, yet there exists a gap in research on the relationship between ecological conditions and patterns of parental care behaviour beyond visitation rate. Here we provide an examination of how bi-parental provisioning behaviours, i.e. pair feeding rate and feeding consistency, and the degree to which parents synchronise or take turns, differ under contrasting ecological conditions in populations of blue tits (Cyanistes caeruleus) spanning a 1000m altitudinal gradient. We found that blue tits pairs synchronised and alternated more than expected by chance, and that care patterns were modified by ecology. Pairs synchronised more in woodland-pasture edges than in woodland interiors, and alternated more and fed more frequently at low altitude compared to higher altitude nests. Variation in bi-parental coordination behaviours did not have a significant impact on fledging success but more synchronous nests had heavier chicks in woodland habitats. Taken as a whole, our results show that patterns of care are influenced by ecological conditions and that their interplay may change the outcome of sexual conflict.

An increase in the perceived risk of predation triggers many behavioural changes in prey species, which can have consequences for their reproductive success. Perceived predation risk may also influence investment in extrapair activities and, as a result, the frequency of extrapair paternity (EPP), but this possibility remains largely untested. Here we report on a study of a small passerine bird, the blue tit, Cyanistes caeruleus, in which we experimentally manipulated perceived predation risk by intermittently broadcasting predator calls throughout the breeding season. We found no evidence that the treatment affected two behavioural indices of extrapair activity (extrabox visits and the time of emergence from the nestbox in the morning during the fertile period) or the rate of EPP itself. The treatment also had no significant effect on clutch size, hatching success or most reproductive behaviours. However, nests in the predator playback treatment produced more fledglings, which was mainly due to a lower frequency of complete brood mortality. We discuss potential explanations for this finding, as well as for the lack of evidence for other effects of the predator playback treatment on blue tit reproductive behaviour. Several measures of reproductive performance suggest that the year in which the experiment took place was an unusually poor one and further work is therefore needed to assess the generality of our findings.

International audience; Understanding species coexistence has long been a major goal of ecology. Coexistence theory for two competing species posits that intraspecific density dependence should be stronger than interspecific density dependence. Great tits and blue tits are two bird species that compete for food resources and nesting cavities. On the basis of long-term monitoring of these two competing species at sites across Europe, combining observational and manipulative approaches, we show that the strength of density regulation is similar for both species, and that individuals have contrasting abilities to compete depending on their age. For great tits, density regulation is driven mainly by intraspecific competition. In contrast, for blue tits, interspecific competition contributes as much as intraspecific competition, consistent with asymmetric competition between the two species. In addition, including age-specific effects of intra-and interspecific competition in density-dependence models improves predictions of fluctuations in population size by up to three times.

This research was funded by the Natural Environment Research Council (NE/J018694/1), the Royal Society (RG2012R2), the M. J. Murdock Charitable Trust (2014199) and the University of St Andrews (University of St Andrews 600th Year Scholarship and the St Leonard’s Fee Scholarship). Mobbing, where birds harass a predator through a combination of vocalizations and stereotyped behaviours, is an effective anti‐predator behaviour for many species. Mobbing may be particularly important for juveniles, as these individuals are often more vulnerable than adults. Although the component behaviours of mobbing are often considered to be un‐learned, there are few confirmatory data, and the developmental trajectory of mobbing is unknown. In this study, we tested whether conspecific or heterospecific mobbing calls initiated mobbing behaviour in juvenile Blue Tits Cyanistes caeruleus. We located wild adult and recently fledged juvenile Blue Tits and presented them with playback recordings of adult conspecific (Blue Tit) and heterospecific (Great Tit Parus major) mobbing alarm calls. Although adult birds readily mob in response to these types of playbacks, juveniles did not exhibit characteristic mobbing behaviour. Some juveniles did, however, exhibit individual components of mobbing behaviour found in mobbing, despite not producing adult‐like mobbing behaviour in response to either conspecific or heterospecific playback. These results suggest that, although birds might be capable of mobbing as juveniles, the associations between the non‐vocal stereotyped mobbing behaviours and mobbing calls may be learned. Postprint

Parasitoid wasps may act as hyperparasites and sometimes regulate the populations of their hosts by a top-down dynamic. Nasonia vitripennis (Walker, 1836) is a generalist gregarious parasitoid that parasitizes several host flies, including the blowfly Protocalliphora Hough, 1899 (Diptera, Calliphoridae), which in turn parasitizes bird nestlings. Nonetheless, the ecological factors underlying N. vitripennis prevalence and parasitoidism intensity on its hosts in natural populations are poorly understood. We have studied the prevalence of N. vitripennis in Protocalliphora azurea (Fallén, 1817) puparia parasitizing wild populations of pied flycatcher (Ficedula hypoleuca) and blue tit (Cyanistes caeruleus) birds in two Mediterranean areas in central and southern Spain. We found some evidence that the prevalence of N. vitripennis was higher in moist habitats in southern Spain. A host-dependent effect was found, since the greater the number of P. azurea puparia, the greater the probability and rate of parasitoidism by the wasp. Our results also suggest that N. vitripennis parasitizes more P. azurea puparia in blue tit nests than in pied flycatcher nests as a consequence of a higher load of these flies in the former. Based on the high prevalence of N. vitripennis in P. azurea puparia in nature, we propose that this wasp may regulate blowfly populations, with possible positive effects on the reproduction of both bird species

Lay Summary The pace-of-life syndrome hypothesis predicts that environmental differences can trigger the evolution of different life-history strategies, including differences in personality. A 5-year study reveals that blue tits breeding in different habitats differ in personality and in life-history characteristics, such as adult survival probability. This is a rare demonstration of personality differences across a small geographical scale, suggesting behavior and life-history traits have coevolved in a local adaptation process., Environmental heterogeneity can result in spatial variation in selection pressures that can produce local adaptations. The pace-of-life syndrome hypothesis predicts that habitat-specific selective pressures will favor the coevolution of personality, physiological, and life-history phenotypes. Few studies so far have compared these traits simultaneously across different ecological conditions. In this study, we compared 3 personality traits (handling aggression, exploration speed in a novel environment, and nest defense behavior) and 1 physiological trait (heart rate during manual restraint) across 3 Corsican blue tit (Cyanistes caeruleus) populations. These populations are located in contrasting habitats (evergreen vs. deciduous) and are situated in 2 different valleys 25 km apart. Birds from these populations are known to differ in life-history characteristics, with birds from the evergreen habitat displaying a slow pace-of-life, and birds from the deciduous habitat a comparatively faster pace-of-life. We expected personality to differ across populations, in line with the differences in pace-of-life documented for life-history traits. As expected, we found behavioral differences among populations. Despite considerable temporal variation, birds exhibited lower handling aggression in the evergreen populations. Exploration speed and male heart rate also differed across populations, although our results for exploration speed were more consistent with a phenotypic difference between the 2 valleys than between habitats. There were no clear differences in nest defense intensity among populations. Our study emphasizes the role of environmental heterogeneity in shaping population divergence in personality traits at a small spatial scale.

The disruption of daily rhythms is one of the most studied ecological consequences of light pollution. Previous work showed that several songbird species initiated dawn song earlier in areas with light pollution. However, the mechanisms underlying this shift are still unknown. Individuals may immediately adjust their timing of singing to the presence of artificial light (behavioural plasticity), but the observed effect may also be due to phenotype-dependent habitat choice, effects of conditions during early life or micro-evolution. The main aim of this study was to experimentally investigate how males of four common passerine species respond to day-to-day variation in the presence of artificial night lighting in terms of the timing of singing. During two consecutive breeding seasons, we manipulated the presence of light throughout the night in a cyclic fashion in several naturally undisturbed forest patches. We show that individuals of all four species immediately and reversibly adjusted their onset of dawn singing in response to artificial light. The effect was strongest in the European robin, but relatively small in the blue tit, the great tit and the blackbird. The effect in the latter two species was smaller than expected from the correlational studies. This may be coincidence (small sample size of this study), but it could also indicate that there are longer-term effects of living in light-polluted urban areas on timing of dawn singing, or that birds use compensatory behaviours such as light avoidance. We found no evidence that our light treatment had carryover effects into the subsequent dark period, but robins progressively advanced their dawn singing during the light treatment.

Many avian species in Europe breed earlier as a result of higher temperatures caused by global climate changes. Climate change means not only higher temperatures but also more frequent extreme weather events, sometimes contrasting with the long-term trends. It was suggested that we should look closely at every extreme phenomenon and its consequences for the phenology of organisms. Examining the limits of phenotypic plasticity may be an important goal for future research. Extremely low spring temperatures in 2013 (coldest spring in 40 years) resulted in birds laying unusually late, and it was followed in 2014 by the earliest breeding season on record (warmest spring in 40 years). Here, we present results concerning breeding phenology and double-broodedness in the Great Tit (Parus major) and the Blue Tit (Cyanistes caeruleus) in 2013 and 2014 in an urban parkland and a deciduous forest in central Poland. Great Tits started laying eggs 18.2 days later in 2013 than in 2014 in the parkland, whereas the analogous difference was 21.1 days in the forest. Blue Tits started laying eggs in the parkland 18.5 days later in 2013 than in 2014, while the analogous difference was 21.6 days in the forest. The difference in the proportion of second clutches in Great Tits between 2013 (fewer second clutches) and 2014 (more second clutches) was highly significant in the parkland and in the forest. This rather large extent of breeding plasticity has developed in reaction to challenges of irregular inter-annual variability of climatic conditions. Such a buffer of plasticity may be sufficient for Blue Tits and Great Tits to adjust the timing of breeding to the upcoming climate changes.

Oxycarenus lavaterae is species of Heteroptera and possessing pink blots on corium and distinctive, gleaming membranaceous wings. This appearance could correspond to the definition of a warning color. The design is similar to other coreoid Heteroptera, which live in the Czech Republic; though Oxycarenus lavaterae is a species originating from Mediterranean and quickly spreading north. In Czech Republic it is a new species and predators thus have only short experience with it.The information about chemical protection of Oxycarenus lavaterae is weak and the effect on predators has never been tested. The characteristic behaviour for this species is creating large aggregations, primarily at the time of hibernation. At that time, several thousands of individuals are gathered in apertures or at the surface of tree bark. The aggregation may enhance the warning appearance of this species. The aim of this study was to test the response of bird predators to the adult individuals of Oxycarenus lavaterae. Three species of insectivorous birds differing in the level of foraging and diet specialization was chosen as predator (namely - Great tit (Parus major), Blue tit (Cyanistes caeruleus), Eurasian blackcap (Sylvia atricapilla)). Unmodified individuals of Oxycarenus lavaterae were served to these predators. In the case of the Parus major, the aggregation of Oxycarenus lavaterae (about 100 pieces) was also presented to test the effect of gregarious behavior on the warning signal. This study showed that the Parus major and the Sylvia atricapilla attacked the individual Oxycarenus more often than the Cyanistes caeruleus showing high level of restraint. In experiments with aggregatedOxycarenus lavaterae Parus major attacked them less often than when presented solitarily. However, after eating some Oxycarenus lavaterae, the Parus major showed symptoms of disgust and loss of appetite.

Despite decades of research, our understanding of the underlying causes of within-population variation in patterns of extra-pair paternity (EPP) remains limited. Previous studies have shown that extra-pair mating decisions are linked to both individual traits and ecological factors. Here, we examine whether social associations among individuals prior to breeding also shape mating patterns, specifically the occurrence of EPP, in a small songbird, the blue tit. We test whether associations during the non-breeding period predict (1) future social pairs, (2) breeding proximity (i.e. the distance between breeding individuals) and (3) the likelihood that individuals have extra-pair young together. Individuals that were more strongly associated (those that foraged more often together) during winter tended to nest closer together. This, by itself, predicts EPP patterns, because most extra-pair sires are close neighbours. However, even after controlling for spatial effects, female–male dyads with stronger social associations prior to breeding were more likely to have extra-pair young. Our findings reveal a carry-over from social associations into future mating decisions. Quantifying the long-term social environment of individuals and studying its dynamics is a promising approach to enhance our understanding of the process of (extra-)pair formation.

Indirect sexual selection arises when reproductive individuals choose their mates based on heritable ornaments that are genetically correlated to fitness. Evidence for genetic associations between ornamental colouration and fitness remains scarce. In this study, we investigate the quantitative genetic relationship between different aspects of tail structural colouration (brightness, hue and UV chroma) and performance (cell-mediated immunity, body mass and wing length) in blue tit (Cyanistes caeruleus) nestlings. In line with previous studies, we find low heritability for structural colouration and moderate heritability for performance measures. Multivariate animal models show positive genetic correlations between the three measures of performance, indicating quantitative genetic variation for overall performance, and tail brightness and UV chroma, two genetically independent colour measures, are genetically correlated with performance (positively and negatively, respectively). Our results suggest that mate choice based on independent aspects of tail colouration can have fitness payoffs in blue tits and provide support for the indirect benefits hypothesis. However, low heritability of tail structural colouration implies that indirect sexual selection on mate choice for this ornament will be a weak evolutionary force.

Evolutionary adaptation as a response to climate change is expected for fitness-related traits affected by climate and exhibiting genetic variance. Although the relationship between warmer spring temperature and earlier timing of reproduction is well documented, quantifications and predictions of the impact of global warming on natural selection acting on phenology in wild populations remain rare. If global warming affects fitness in a similar way across individuals within a population, or if fitness consequences are independent of phenotypic variation in key-adaptive traits, then no evolutionary response is expected for these traits. Here, we quantified the selection pressures acting on laying date during a 24-year monitoring of blue tits in southern Mediterranean France, a hot spot of climate warming. We explored the temporal fluctuation in annual selection gradients and we determined its temperature-related drivers. We first investigated the month-specific warming since 1970 in our study site and tested its influence on selection pressures, using a model averaging approach. Then, we quantified the selection strength associated with temperature anomalies experienced by the blue tit population. We found that natural selection acting on laying date significantly fluctuated both in magnitude and in sign across years. After identifying a significant warming in spring and summer, we showed that warmer daily maximum temperatures in April were significantly associated with stronger selection pressures for reproductive timing. Our results indicated an increase in the strength of selection by 46% for every +1°C anomaly. Our results confirm the general assumption that recent climate change translates into strong selection favouring earlier breeders in passerine birds. Our findings also suggest that differences in fitness among individuals varying in their breeding phenology increase with climate warming. Such climate-driven influence on the strength of directional selection acting on laying date could favour an adaptive response in this trait, since it is heritable.

International audience; To anticipate future breeding conditions in spatiotemporally dynamic environments, any proximate aspect of breeding is expected to be causally associated with environmental cues or constraints. Photoperiod, ambient temperature, and food are considered to be among the most important environmental determinants of breeding performance. However, the importance of these determinants in the expression of nest size has not previously been investigated experimentally in laboratory conditions. We report that captive Blue Tits (Cyanistes caeruleus) and Great Tits (Parus major) did not adjust the size of their cavity nest to experimental changes in photoperiod or ambient-temperature regimes. Results did not change when we controlled for first-egg date and clutch size. In addition, captive birds fed ad libitum did not build larger nests than free-ranging breeders in standardized nest boxes. Thus, we report no evidence that nest size per se is proximately influenced by commonly studied environmental factors like photoperiod, temperature, food abundance, or the level of investment in egg production-factors that can all pose energetic challenges to breeding birds. However, we do not exclude the possibility that, in natural conditions, energy- or resource-associated constraints might influence aspects of nest design other than nest size (e.g., rare nest components) or that constraints on nest building might only be revealed when birds need to build substantially larger nests (i.e. in larger cavities). Therefore, additional experimental work will be required to determine which are the proximate determinants of nest design in cavity breeders.

Comparación de la composición y el tamaño de las presas que el carbonero común (Parus major) y el herrerillo común (Cyanistes caeruleus) aportan a sus pollos en un bosque mediterráneo mixto esclerófilo La división de los recursos es un aspecto esencial en ecología porque puede determinar hasta qué punto pueden coexistir especies parecidas en un mismo hábitat. El carbonero común y el herrerillo común son especies que se utilizan tradicionalmente como modelo en los estudios sobre competencia trófica. No obstante, la mayoría de los estudios sobre este tema se han llevado a cabo en localidades en las que las orugas son, con diferencia, la presa que más se aporta a los pollos. Sin embargo, en los bosques mixtos mediterráneos la abundancia de orugas es relativamente escasa y son las arañas el elemento fundamental de la alimentación del carbonero común, al menos para los pollos. El objetivo del presente artículo es estudiar el aporte de alimentos al nido para establecer el grado de solapamiento de la dieta entre estas dos especies de paros en un bosque mediterráneo. Nuestros resultados mostraron que la tasa de alimentación del herrerillo común es superior a la del carbonero común, probablemente para compensar el hecho de que las presas que el herrerillo lleva a los pollos son de menor tamaño. El herrerillo común aportó más arañas que el carbonero, pese a que el carbonero gris llevó presas de mayor tamaño y más cantidad de orugas. Ello se debe a que el carbonero común puede cazar presas más grandes que el herrerillo. El principal resultado de este estudio respalda la hipótesis de la división de recursos entre el carbonero común y el herrerillo común en un ecosistema forestal mediterráneo esclerófilo., Resource partitioning is a central issue in ecology because it can establish to which point similar species can coexist in the same habitat. Great tits and blue tits have beenclassical model species in studies of trophic competence. However, most studies on the topic have been conducted atlocalities where caterpillars are by far the most relevant prey brought to the nestlings. In Mediterranean mixed forests,nevertheless, the abundance of caterpillars is relatively low and it is spiders that play a key role in the diet of great tits,at least for nestlings. The aim of this paper was to study nest food provisioning to establish the degree of diet overlapof these two tit species in a Mediterranean forest. Our results showed that blue tit feeding rates were higher than thoseof great tits, probably to compensate for the smaller prey delivered to nestlings by blue tits. Blue tits brought morespiders than great tits, while grey tits brought larger prey and more caterpillars. This may be because larger great titscan prey upon larger prey items than blue tits. As a main result, this study supports the view of resource partitioningby great and blue tits in sclerophyllous Mediterranean forest ecosystem

Anthropogenic noise levels are steadily increasing worldwide and may potentially affect many species. Short-term experimental noise exposure under field and lab conditions has revealed that noise can affect the behavior and physiology of birds. However, few studies have been able to link these short-term effects to longer-term consequences. Here, we report on 2 long-term noise exposure field experiments to assess the direct and indirect effects of noise on avian reproductive success. In one experiment, we provided 2 types of nesting sites in our study area, a nest-box with traffic noise broadcast inside, as well as a control nest-box. We found great tits (Parus major) to avoid breeding in noisy nest-boxes, in particular when they had both nest-box types available in their territory. Interestingly, we found blue tits (Cyanistes caeruleus) to breed more often in the noisy nest-boxes compared with the control nest-boxes. In another experiment, we randomly assigned nest-box treatments to breeding great tits after settlement and started noise exposure prior to egg laying or hatching. We found no significant effect of noise treatment on clutch size, number of fledglings, or any other life-history trait we measured. Our results show that great tits avoid breeding in noisy locations. Birds that are however forced to breed in noise, either through experimental manipulation or potentially through competitive exclusion, do not suffer from reduced reproductive success. Thus, anthropogenic noise can affect settlement behavior, but breeding inside a noisy nest-box has no reproductive consequences, at least not for great tits.

While the study of the origins of biological diversity across species has provided numerous examples of adaptive divergence, the realization that it can occur at microgeographic scales despite gene flow is recent, and scarcely illustrated. We review here evidence suggesting that the striking phenotypic differentiation in ecologically relevant traits exhibited by blue tits Cyanistes caeruleus in their southern range‐edge putatively reflects adaptation to the heterogeneity of the Mediterranean habitats. We first summarize the phenotypic divergence for a series of life history, morphological, behavioural, acoustic and colour ornament traits in blue tit populations of evergreen and deciduous forests. For each divergent trait, we review the evidence obtained from common garden experiments regarding a possible genetic origin of the observed phenotypic differentiation as well as evidence for heterogeneous selection. Second, we argue that most phenotypically differentiated traits display heritable variation, a fundamental requirement for evolution to occur. Third, we discuss nonrandom dispersal, selective barriers and assortative mating as processes that could reinforce local adaptation. Finally, we show how population genomics supports isolation – by – environment across landscapes. Overall, the combination of approaches converges to the conclusion that the strong phenotypic differentiation observed in Mediterranean blue tits is a fascinating case of local adaptation.

Environmental heterogeneity in space and time plays a key role in influencing trait variability in animals, and can be particularly relevant to animal phenology. Until recently, the use of remotely sensed imagery in understanding animal variation was limited to analyses at the population level, largely because of a lack of high-resolution data that would allow inference at the individual level. We evaluated the potential of SPOT 4 (Take 5) satellite imagery data (with observations every fifth day at 20 m resolution and equivalent to acquisition parameters of Sentinel-2) in animal ecology research. We focused on blue tit Cyanistes caeruleus reproduction in a study site containing 227 nestboxes scattered in a Mediterranean forest dominated by deciduous downy oaks Quercus pubescens with a secondary cover of evergreen holm oaks Quercus ilex. We observed high congruence between ground data collected in a 50 m radius around each nestbox and NDVI values averaged across a 5 by 5 pixel grid centered around each nestbox of the study site. The number of deciduous and evergreen oaks around nestboxes explained up to 66% of variance in nestbox-centered, SPOT-derived NDVI values. We also found highly equivalent patterns of spatial autocorrelation for both ground- and satellite-derived indexes of environmental heterogeneity. For deciduous and evergreen oaks, the derived NDVI signal was highly distinctive in winter and early spring. June NDVI values for deciduous and evergreen oaks were higher by 58% and 8% relative to February values, respectively. The number of evergreen oaks was positively associated with later timing of breeding in blue tits. SPOT-derived, Sentinel-2 like imagery thus provided highly reliable, ground-validated information on habitat heterogeneity of direct relevance to a long-term field study of a free-living passerine bird. Given that the logistical demands of gathering ground data often limit our understanding of variation in animal reproductive traits across time and space, there appears to be great promise in applying fine-resolution satellite data in evolutionary ecology research.

Evidentno, posljednjih stotinu godina došlo je do klimatskih promjena na našem planetu. Brojne promjene kod biljaka i životinja povezuju se sa klimatskim zatopljenjem, što je dokumentirano u velikom broju znanstvenih radova posljednjih dvadesetak godina. U većini slučajeva, glavni pokretač tih promjena je temperatura zraka. Najviše publiciranih članaka u vezi klimatskog zatopljenja i ptica odnosi se na fenologiju. Između ostalog, studije upućuju da je kod brojnih ptičjih vrsta došlo do ranijeg gniježđenja u posljednjih nekoliko desetljeća. Tijekom ovog istraživanja utvrđivan je trend nesidbe na temelju uzorkovanja nesenja prvog jajeta u gnijezdu lokalne populacije ptice stanarice i dupljašice plavetne sjenice (Cyanistes caeruleus) u nizinskim listopadnim šumama (prevladava hrast lužnjak Quercus robur L. i obični grab Carpinus betulus L.) u razdoblju od 1982. do 2016. godine na dijelu sjeverozapadne Hrvatske. Analiziran je i odnos između početka nesidbe i srednje proljetne temperature zraka. Podaci o polaganju jaja uzimani su iz drvenih škrinjica (umjetnih duplji) za gniježđenje ptica. Brojni ornitološki radovi temelje se na korištenju spomenutih umjetnih duplji. Sva uzorkovanja obavio je autor ovog članka. Srednja se proljetna temperature zraka značajno povećala tijekom istraživanja (od 1982. do 2016. godine). Odnos između datuma polaganja jaja i godina istraživanja bio je također statistički signifikantan. Datum početka nesidbe plavetne sjenice uznapredovao je za 11 dana u 35-godišnjem razdoblju. Dobiveni rezultati sugeriraju da je porastom proljetnih temperatura zraka tijekom dugogodišnjeg razdoblja došlo do ranijeg gniježđenja plavetne sjenice u nizinskim listopadnim šumama sjeverozapadne Hrvatske kao posljedica fenotipske plastičnosti. Očito, istraživana šumska populacija plavetne sjenice u stanju je nositi se s porastom proljetne temperature, čemu u prilog nam govori i relativna stabilnost populacije., In the last 100 years, climate warming (climate change) phenomenon has been present on our planet. Numerous biological features of organisms have been linked to climate change and many papers in the last few decades have illustrated changes in natural biological systems. In most cases, these responses are associated with changes in air temperature. In birds, most of the published works are looking at phenology. Such studies suggest that the laying date is advancing. In this study, I examined long-term changes in the date of clutch initiation in sedentary local hole-nesting population of the Blue Tit (Cyanistes caeruleus) in deciduous forest (dominated Pediculate Oak Quercus robur L. and Common Hornbeam Carpinus betulus L.) from 1980 to 2016 (northwestern Croatia). Also, I examined relationship between timing of breeding and mean spring air temperature. All the records used in this work, as well as numerous ornithological papers around the world have been based on the use of nest-boxes by birds. The boxes were placed on the trees, at 2.5 to 4 m above ground and all nest-boxes had a sliding top in order to monitor nest. All observations were recorded by the author. Spring mean local air temperatures during research period have significant increase. Relationship between laying date and year was also significant. The breeding date in researched species has advanced by 11 days in study period. According to my results, sedentary local population of the Blue Tit in northwestern Croatia was able to respond to spring warming changes during 37-year period.

Understanding the causes and consequences of population phenotypic divergence is a central goal in ecology and evolution. Phenotypic divergence among populations can result from genetic divergence, phenotypic plasticity or a combination of the two. However, few studies have deciphered these mechanisms for populations geographically close and connected by gene flow, especially in the case of personality traits. In this study, we used a common garden experiment to explore the genetic basis of the phenotypic divergence observed between two blue tit (Cyanistes caeruleus) populations inhabiting contrasting habitats separated by 25 km, for two personality traits (exploration speed and handling aggression), one physiological trait (heart rate during restraint) and two morphological traits (tarsus length and body mass). Blue tit nestlings were removed from their population and raised in a common garden for up to five years. We then compared adult phenotypes between the two populations, as well as trait‐specific Qst and Fst. Our results revealed differences between populations similar to those found in the wild, suggesting a genetic divergence for all traits. Qst ‐ Fst comparisons revealed that the traits divergences likely result from dissimilar selection patterns rather than from genetic drift. Our study is one of the first to report a Qst ‐ Fst comparison for personality traits and adds to the growing body of evidence that population genetic divergence is possible at a small scale for a variety of traits including behavioural traits.