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Climate change affects timing of reproduction in many bird species, but few studies have investigated its influence on annual reproductive output. Here, we assess changes in the annual production of young by female breeders in 201 populations of 104 bird species (N = 745,962 clutches) covering all continents between 1970 and 2019. Overall, average offspring production has declined in recent decades, but considerable differences were found among species and populations. A total of 56.7% of populations showed a declining trend in offspring production (significant in 17.4%), whereas 43.3% exhibited an increase (significant in 10.4%). The results show that climatic changes affect offspring production through compounded effects on ecological and life history traits of species. Migratory and larger-bodied species experienced reduced offspring production with increasing temperatures during the chick-rearing period, whereas smaller-bodied, sedentary species tended to produce more offspring. Likewise, multi-brooded species showed increased breeding success with increasing temperatures, whereas rising temperatures were unrelated to reproductive success in single-brooded species. Our study suggests that rapid declines in size of bird populations reported by many studies from different parts of the world are driven only to a small degree by changes in the production of young., This meta-analysis was financed by the grant of the Polish National Science Centre (Narodowe Centrum Nauki) (no. 2017/27/B/NZ8/00465) awarded to Lucyna Hałupka.

Knowing how animals adapt their phenotype to local temperature and humidity is key to understanding not only ecogeographical rules, but also how species will manage climate change, as current models predict changes in global patterns of temperature and precipitation. In endotherms, colour adaptations in response to climate have been under investigated, and their acclimatization-the individual capacity to reversibly adjust phenotype in response to different environments-is unknown. Geographic trends can provide clues about abiotic variables involved in colouration, as postulated by Gloger’s rule, which predicts darker individuals in warm and humid regions. We tested whether house sparrows (Passer domesticus) can adjust colouration when faced with varying humidity conditions. We exposed birds to either a dry (humidity 45%) or a wet environment (70%) six months before their moult, and measured colouration in newly developed feathers in five parts of the body (bib, crown, crown stripe, belly and rump). As predicted by Gloger’s rule, birds in wet conditions developed darker (bib and belly) and larger (bib) melanised plumage patches, than birds in dry conditions. Our result provides the first unequivocal evidence that the ability of individual birds to adjust their colouration may be a potential adaptation to climatic changes in endotherms., Research was funded by the Ministerio de Ciencia e Innovación through project PID2019-111039GA-100.

[Aim]: Oceanic islands have often been colonized by small groups of individuals dispersing from the nearest mainland, giving rise to insular populations characterized by locally adapted phenotypes and low genetic diversity. Alternatively, due to past geo‐climatic changes, the present‐day distribution of the species may not correspond to that found at the time of the original colonization so that the current mainland distribution may not include the original source area, leading to erroneous assumptions regarding colonization history. Here, we use patterns of genetic variation to evaluate alternative colonization scenarios of an insular passerine in the Canary Islands., [Location]: La Palma (Canary Islands), Northern Africa and the Iberian Peninsula., [Taxon]: Red‐billed chough (Pyrrhocorax pyrrhocorax)., [Methods]: We use phylogeographical and coalescent analyses of mitochondrial DNA sequences and 10 microsatellite loci, together with Bayesian demographic modelling, to determine whether choughs on the island of La Palma originate from (a) present‐day populations in Iberia, (b) present‐day populations in the mountains of inland Morocco or (c) former populations in coastal Morocco, where suitable habitat existed in the past., [Results]: Both the mitochondrial and nuclear datasets indicate that the chough population on La Palma is genetically well differentiated from those in Iberia and Morocco, and that La Palma choughs are more closely related to choughs in Iberia than to those in Morocco. Genetic diversity in La Palma is lower than that of mainland populations, but shows no evidence of past bottlenecks. The best supported demographic model to explain the origin of La Palma choughs that is congruent with both genetic datasets includes a ‘ghost’ population closely related to Iberia, from which the insular population diverged within the last 30,000 years., [Main conclusions]: Our results are most consistent with the existence of a former connection between La Palma and Iberia along the North African coast, when suitable habitat was found there. Subsequent desertification of these coastal areas led to local extinctions that restricted gene flow between Iberia and the islands, promoting genetic differentiation. Our results provide a counterintuitive solution to a biogeographical enigma, and could help resolve the colonization history of other systems with similarly complex climatic pasts., The study was funded by projects from the Junta de Comunidades de Castilla‐La Mancha (PPIC10‐0094‐3036), the Spanish Ministry of the Environment (082/2002) and the Ministry of Science and Education (BOS2003‐05066 and CGL2015‐66381‐P). F. M. was supported by a Juan de la Cierva postdoctoral fellowship from Spain's Ministry of Science and Innovation (FJCI‐2017‐32055) for part of this work.

Optimal foraging theory has typically paid little attention to species feeding on mobile prey and has emphasised energy intake rather than the nutritional contribution of food. The difficulty of capturing food has rarely been included in foraging models, even when it is a potentially important modulator of time devoted to foraging. From the central place foraging and provisioning perspectives, it is posited that at high levels of prey selectivity, the time spent to capture prey is longer than at low levels of prey selectivity. Furthermore, in the case of carnivorous predators, it is thought that nutritional composition does not influence foraging strategies. To explore these issues, we investigated the influence of abundance, size, difficulty of capture, gross energy and nutritional composition (fat, protein, protein-fat ratio and amino acid contents) of prey species on the foraging behaviour of a predator species, the common kestrel Falco tinnunculus, in a region of high diversity of prey species. Our results show that capturability index and load-size explain the foraging behaviour of kestrels. Preferred prey take longer to be provisioned, both selectivity and capturability might explain this result. It is also shown that specific nutritional components, such as protein and amino acid contents, are likely to explain food preference in this carnivorous-insectivorous species., was supported by a Formación de Personal Investigador (FPI) grant from Ministerio de Economía y Competitividad (MIMECO). Research was funded by the Ministerio de Economía y Competitividad (MINECO) through projects CGL2007–61395, CGL2010–15726, CGL2013–42451-P and PGC2018–095070-B-I00. This is a contribution of the El Ventorrillo Biological Station.

Damage associated with rodent’s outbreaks is common in the actual intensive agriculture. In order to reduce these economic losses, the placement of nest boxes for raptors could be a useful alternative to the chemical control programs. Barn owl (Tyto alba) and common kestrel (Falco tinnunculus) are two of the most commonly used species as rodent biological controls. The increase of the density of these two raptors is able to reduce the rodent’s abundance without the huge negative impact caused by the use of chemical products in surrounding biodiversity. However, other prey species could be affected by these raptors too. In order to evaluate the different impacts of barn owl and common kestrel on non-pest species, we studied the diet in 50 paired nest boxes during 3 consecutive years, based on 1249 pellets. The proportion of small mammals considered pests for agriculture (voles and mice) consumed by barn owl (80%) and common kestrel (75.6%) were quite similar. Based on nutritional requirements, nest-box occupancy probability and productivity, we estimated a consumption of 5.24 rodents per day per common kestrel nest-box placed and of 4.95 rodents per barn owl nest-box placed. However, shrews were significantly more captured by barn owl and birds were significantly more captured by common kestrel. Our results showed that both species of raptors can be effective in controlling rodents that are harmful to agriculture, but the common kestrel seemed to be slightly more efficient and might also prey on insect taxa that could be important agricultural pests., Sample collection was included in the technical assistance in biological pest control, performed by Navarra Environmental Management (GAN-NIK) and financed by the Sanidad Vegetal Section of the Agriculture Department of the Navarra government. G.M. was supported by a Serra Húnter felow. The rest of the work was carried out without any economic support.

Several studies have shown that melanin‐based traits play a crucial role in social contexts as they are associated with dominance, personality and social behaviour. However, most of these studies have focused on adults, and the role of these traits in juveniles remains scarcely explored. Here, we explore the association between two melanin‐based traits and nestling personality in Common Kestrels Falco tinnunculus. Our results show that female nestlings with blacker plumages displayed bolder personalities, providing evidence of sex‐dependent phenotypic integration of these two traits in males and females. We consider that this differential integration may arise from different selection pressures acting on males and females on plumage colouration during adulthood and that nestling colouration can act as a status signal within the juvenile age‐class., The study was financed by the Spanish Ministerio de Economía y Competitividad (Project: CGL2013-42451-P). DLI is supported by a postdoctoral contract of the REMEDINAL3-CM program of Comunidad Autónoma de Madrid (REF: S2013/MAE-2719)

Order of birth has profound consequences on offspring across taxa during development and can have effects on individuals later in life. In birds, differential maternal allocation and investment in their progeny lead to variance in the environmental conditions that offspring experience during growth within the brood. In particular, laying and hatching order have been proposed to influence individual quality during the growing period, but little is known about the fitness consequences that these two factors have for offspring from a lifetime perspective. We explored the effect of laying and hatching order on post‐fledgling survival (measured as recruitment probability) and lifetime reproductive success (LRS) in Common Kestrels Falco tinnunculus, using a long‐term and individual‐based dataset. First‐hatched chicks showed higher survival probability and LRS than their siblings. This effect was not due to body condition of the individuals at adulthood, the quality of their mates or the reproductive outcome compared with later‐hatched individuals. Instead, first‐hatched chicks had a higher recruitment probability. This could be explained by the higher body condition attained by first‐hatched chicks at the end of the nesting period, perhaps due to an enhanced competitive advantage for food over their siblings at the time of hatching. Laying order, in contrast to hatching order, appeared to have little or no effect on LRS. Our results suggest that hatching order within siblings predicts fitness, and that better early‐life conditions during growth experienced by first‐hatched chicks improve first survival and then recruitment, resulting in an enhanced LRS., This study was financed by the Spanish Ministerio de Economía y Competitividad (Projects: CGL2004‐04479/BOS; CGL2007‐61395/BOS; CGL2010‐15726/BOS; CGL2015‐70639‐P). Suggestions from R. Kimball and two anonymous referees greatly improved an early version of this paper. This study was conducted in accordance with all applicable laws and rules set forth by the Spanish Government and all licences granted by Junta de Castilla y León.

Open Access., [EN]: Birds of prey have been, in comparison to other avian groups, an uncommon study model, mainly due to the limitations imposed by their conservative life strategy (low population density and turnover). Nonetheless, they have attracted a strong interest from the point of view of conservation biology because many populations have been close to extinction and because of their recognised role in ecosystems as top predators and scavengers and as flagship species. Today, after more than a century of persecution, and with the exception of some vultures still very much affected by illegal poisoning, many populations of birds of prey have experienced significant recoveries in many regions of Spain and the European Mediterranean. These changes pose new challenges when addressing the conservation of raptors in the coming decades. On this basis, and from a preferentially Mediterranean perspective, we have focused our attention on the need of describing and quantifying the role of these birds as providers of both regulating (rodent pest control and removal of livestock carcasses) and cultural ecosystem services. Moreover, we revisited persisting conflicts with human interests (predation of game species) and call attention to the emergence of new conflicts with a strong social and media component such as the predation on live cattle by vultures. Also, the rampant humanization of the environment determines the need for new solutions to the growing, yet scarcely explored, problem of accidents in new infrastructures such as mortality in wind farms. Finally, we explored in depth the ecological response of birds of prey to large-scale habitat changes such as urbanisation and abandonment of marginal lands that are also expected to increase in the near future. We urgently need more scientific knowledge to provide adequate responses to the challenge of keeping healthy populations of avian predators and scavengers in a rapidly changing world., [ES]: Las aves de presa han sido, en comparación con otros grupos de aves, más raramente utilizadas como sujeto de estudios en ecología en razón de las limitaciones que impone su estrategia de vida (baja densidad de población, alta longevidad y baja natalidad). Por el contrario, han suscitado un gran interés desde el punto de vista de la biología de la conservación, debido a que sus poblaciones en muchos casos se han aproximado a la extinción, así como al reconocimiento de su papel en los ecosistemas como superpredadores y carroñeros como especies bandera. Hoy en día, tras más de un siglo de persecución, y con la excepción de algunos buitres todavía muy afectados por envenenamientos ilegales, muchas especies de aves de presa han experimentado importantes crecimientos poblacionales en muchas regiones de España y del Mediterráneo europeo. Este escenario plantea nuevos desafíos para abordar la conservación de las rapaces en las próximas décadas. Sobre esta base hemos focalizado nuestra atención en la necesidad de describir y cuantificar el papel de estas aves como proveedores de servicios ecosistémicos, tanto reguladores (control de plagas de roedores y eliminación de restos de ganado) como culturales y de apoyo. Por otra parte, llamamos la atención hacia el reavivamiento de conflictos con intereses humanos (predación sobre especies cinegéticas) y a la aparición de nuevos conflictos con un fuerte componente social y mediático como la predación de aves carroñeras sobre ganado vivo. De igual modo, la creciente humanización del medio y de las poblaciones de aves de presa de mayor tamaño determinan que haya que buscar nuevas soluciones a problemas ya conocidos como los accidentes en infraestructuras, pero que tienen nuevas facetas complejas y aun poco exploradas como la mortalidad en parques eólicos. Finalmente, nos adentramos en la respuesta de las aves de presa a cambios a gran escala en el hábitat, como la urbanización y el abandono de tierras marginales que ya están ocurriendo y se prevé que se incrementen en las próximas décadas. Debe generarse más conocimiento científico para poder dar adecuada respuesta al reto que supone mantener poblaciones sanas de aves predadoras y carroñeras en un mundo que cambia vertiginosamente., M. M. acknowledges financial support through the Severo Ochoa Program for Centres of Excellence in R+D+I (SEV-2012-0262), z. M. R. was supported by a pre-doctoral grant FPU12/00823. A. M. was supported by a Ramón y Cajal research contract (Ministry of Economy and Competitiveness, RYC-2012-11867). ACA was supported by a Post-Doctoral grant from the Fundação para a Ciência e a Tecnologia (FCT) (SFRH / BPD / 91609 / 2012) and a contract Juan de la Cierva Incorporación IJCI-2014-20744 of the Ministry of Economy and Competitiveness. JAD, JMPG, AM, zM and JASz were funded by project CGL2015-66966-C2-1-2-R, MINECO/FEDER, UE.

Two opposite phenomena have been found in territorial animals, the “dear enemy’’ and the “nasty neighbour’’, which refer to individuals that show less aggression toward neighbours than toward strangers and vice versa. However, the need to maintain territory should differ for males and females because sexual reproduction is the result of the different adaptive strategies of the sexes. In this study, we explore territorial behaviour in the context of dear-enemy and nasty neighbour effects in the Mexican volcano mouse (Neotomodon alstoni). Patterns of spatial relationships between individuals and the degrees of agonistic behaviour among neighbours were analysed for a period of one year. Results exhibit a greater spatial proximity between male pairs during the non-reproductive period than during the reproductive period, and greater spatial proximity between pairs of females during the reproductive period than during the non-reproductive period. The analysis of agonistic behaviour showed that there is less tolerance for distant neighbours than for nearest neighbours. However, there is a greater frequency of aggression between male pairs than between females, while females appear to exhibit non-aggressive avoidance among individuals. The results support the theory that Mexican volcano mouse exhibits the "dear enemy phenomenon"., This work was supported by grants from Cuerpos Académicos (Ecología Fisiológica y del Comportamiento en Ambientes Naturales y Antropizados UATLX-CA-227).

To understand whether early phenotypes are adaptive, knowledge of the environmental factors involved in their variation and the derived benefits from their expression is needed. Temperature and sunlight are considered two major selective forces influencing phenotypic coloration of birds at a global scale. However, within-population color adaptations in response to sunlight temperature variation have been scarcely investigated, and their acclimatization capacity is currently unknown. In addition, the sexes differ in their sensitivity to environmental factors during growth. This study evaluates how melanin plumage coloration varies in relation to sex and sunlight exposure in developing griffon vultures Gyps fulvus and how this correlates with survival. The results show that individuals grown in nests more exposed to sunlight developed paler plumages, as predicted by the thermal melanism hypothesis. In addition, paler males—but not females—have lower survival probability. Finally, a significant sexual dichromatism in fledgling plumage was observed, with females being paler than males. These results reveal within-population color variation related to sunlight temperature conditions, probably as a capacity for local acclimatization through color plasticity, and also provide evidence of sex differences in fitness optima for this trait under ecological pressures.

Sexual dimorphism (SD) has evolved in response to selection pressures that differ between sexes. Since such pressures change across an individual's life, SD may vary within age classes. Yet, little is known about how selection on early phenotypes may drive the final SD observed in adults. In many dimorphic species, juveniles resemble adult females rather than adult males, meaning that out of the selective pressures established by sexual selection feminized phenotypes may be adaptive. If true, fitness benefits of early female-like phenotypes may constrain the expression of male phenotypes in adulthood. Using the common kestrel Falco tinnunculus as a study model, we evaluated the fitness advantages of expressing more feminized phenotypes at youth. Although more similar to adult females than to adult males, common kestrel fledglings are still sexually dimorphic in size and coloration. Integrating morphological and chromatic variables, we analysed the phenotypic divergence between sexes as a measure of how much each individual looks like the sex to which it belongs (phenotypic sexual resemblance, PSR). We then tested the fitness benefits associated with PSR by means of the probability of recruitment in the population. We found a significant interaction between PSR and sex, showing that in both sexes more feminized phenotypes recruited more into the population than less feminized phenotypes. Moreover, males showed lower PSR than females and a higher proportion of incorrect sex classifications. These findings suggest that the mechanisms in males devoted to resembling female phenotypes in youth, due to a trend to increase fitness through more feminized phenotypes, may provide a mechanism to constrain the SD in adulthood., This study was financed by the Spanish Ministerio de Economíıa y Competitividad (Projects: CGL2004-04479/BOS, CGL2007-61395/BOS, CGL2010-15726/BOS).

Knowledge of the genetic basis of sexual ornaments is essential to understand their evolution through sexual selection. Although carotenoid-based ornaments have been instrumental in the study of sexual selection, given the inability of animals to synthesize carotenoids de novo, they are generally assumed to be influenced solely by environmental variation. However, very few studies have directly estimated the role of genes and the environment in shaping variation in carotenoid-based traits. Using long-term individual-based data, we here explore the evolutionary potential of a dynamic, carotenoid-based ornament (namely skin coloration), in male and female common kestrels. We first estimate the amount of genetic variation underlying variation in hue, chroma and brightness. After correcting for sex differences, the chroma of the orange-yellow eye ring coloration was significantly heritable (h2 ± SE = 0.40 ± 0.17), whereas neither hue (h2 = 0) nor brightness (h2 = 0.02) was heritable. Second, we estimate the strength and shape of selection acting upon chromatic (hue and chroma) and achromatic (brightness) variation and show positive and negative directional selection on female but not male chroma and hue, respectively, whereas brightness was unrelated to fitness in both sexes. This suggests that different components of carotenoid-based signals traits may show different evolutionary dynamics. Overall, we show that carotenoid-based coloration is a complex and multifaceted trait. If we are to gain a better understanding of the processes responsible for the generation and maintenance of variation in carotenoid-based coloration, these complexities need to be taken into account.

The intensity of color expression in animals plays a key role in social environments as a mechanism to signal individual capacities in competitive contests. Selective pressures for resource competition differ at different stages of life and between sexes; therefore, coloration is expected to vary between juveniles and adults and between males and females. Exploring the covariance between coloration and other traits may help to understand the functional significance of color and the action of natural selection on multivariate phenotypes. Melanin-based plumage coloration was investigated in the masked booby Sula dactylatra in relation to melanin concentration, sex, hormone levels, and shy-bold behavior of chicks close to fledging. Darker brown boobies showed higher levels of both eumelanin and pheomelanin concentration and lower body mass. Males behaved bolder than females and showed on average 8% larger brown patches. Bolder females had smaller brown patches. Bolder individuals also had lower levels of circulating testosterone, but no differences in corticosterone levels were found. Stronger phenotypic integration was observed in females than males. Our study suggests that juvenile melanic coloration may reflect behavioral strategies by sex, endocrine profiles, and body mass indicating the convergence of different adaptive functions in a given phenotype, this being more evident in females. Direction of correlations differed from those predicted under the pleiotropic idea for color-related traits. These results suggest the possibility that juvenile plumage acts as a signaling system in a social context within the age class and suggest that plumage coloration may indicate different behavioral strategies. © The Author 2013., The study was supported by Spanish Ministerio de Ciencia e Innovación (CGL2009-10883-C02-01; CGL2012-40229-C02-02).

Adaptation to insular environments often arises from changes and innovations in feeding behaviour allowing expanded foraging habits and an increased niche breadth. These shifts and innovations have traditionally been thought to be related to community-wide processes, but could also be the direct result of environmental constraints determining the abundance, availability and suitability of a particular food providing specific nutrients for survival, growth and reproduction. The link between environmental constraints on nutrients and life-history of insular organisms can help in understanding the convergent set of adaptations sustaining the ‘island syndrome’. We tested whether a potential insular nutrient shortage can drive diet shifts, nutritional biochemistry and growth stress, thus contributing to the modulation of life-history traits in a large passerine bird, the red-billed chough (Pyrrhocorax pyrrhocorax). Results supported the insular nutritional challenge hypothesis, linked to an insular insect shortage. An insect shortage may in turn have determined the reduced consumption of this source of protein but increased consumption of other arthropods, and notably fruits, by insular nestlings and fully-grown individuals. Island birds showed comparatively low circulating levels of nutrients and metabolites associated with the consumption of protein-rich animal matter as opposed to carbohydrate-rich vegetal matter, as well as high growth stress reflected in poor feather quality. We propose that feeding shifts derived from an insular insect shortage may exert a strong influence on the allocation of limited time, energy and nutrients among competing functions associated with physiological changes and investment in reproduction and self-maintenance. Traits and patterns generally defining the insular syndrome could thus be linked to particular insular nutrient constraints forcing feeding shifts and nutritional challenges with physiological, demographic and life-history consequences.

The genetic covariation among different traits may cause the appearance of correlated response to selection on multivariate phenotypes. Genes responsible for the expression of melanin-based color traits are also involved in other important physiological functions such as immunity and metabolism by pleiotropy, suggesting the possibility of multivariate evolution. However, little is known about the relationship between melanin coloration and these functions at the additive genetic level in wild vertebrates. From a multivariate perspective, we simultaneously explored inheritance and selection of melanin coloration, body mass and phytohemagglutinin (PHA)-mediated immune response by using long-term data over an 18-year period collected in a wild population of the common kestrel Falco tinnunculus. Pedigree-based quantitative genetic analyses showed negative genetic covariance between melanin-based coloration and body mass in male adults and positive genetic covariance between body mass and PHA-mediated immune response in fledglings as predicted by pleiotropic effects of melanocortin receptor activity. Multiple selection analyses showed an increased fitness in male adults with intermediate phenotypic values for melanin color and body mass. In male fledglings, there was evidence for a disruptive selection on rump gray color, but a stabilizing selection on PHA-mediated immune response. Our results provide an insight into the evolution of multivariate traits genetically related with melanin-based coloration. The differences in multivariate inheritance and selection between male and female kestrels might have resulted in sexual dimorphism in size and color. When pleiotropic effects are present, coloration can evolve through a complex pathway involving correlated response to selection on multivariate traits.

Intrasexual competition in female birds is a widespread phenomenon but remains scarcely explored. Females compete for limited resources and the expression of signals that indicate their social status will be favoured by natural selection, generating a dominance hierarchy among individuals. However, which signals might be involved in female–female competition is unclear. In this study, we tested the role of rump coloration as a badge of status within a context of intrasexual competition using common kestrels, Falco tinnunculus, in two populations over 3 years. We used natural decoys with two different ‘phenotypes’, since the expression of this melanin-pigmented trait within the brown–grey range has been suggested to be a reliable proxy of individual quality in female common kestrels. By showing natural decoys with grey and brown rumps to breeding females, we simulated territorial invasions of high- and low-quality females, respectively. Our results show that rump coloration generates a differential response during territorial invasions. Specifically, we found that grey-rumped decoys (high quality) elicited lower levels of aggressiveness. In addition, female agonistic response was negatively associated with clutch size. Based on our results, we suggest that female rump coloration works as a badge of status in breeding female kestrels. This trait may signal female competitive ability and can generate a dominance hierarchy among individuals in our population. We also suggest that aggressiveness can be costly to females in terms of reproductive outcome. Overall, we provide evidence that melanin-pigmented traits in females can play a key role in intrasexual competition., This study was financed by the Spanish Ministerio de Economía y Competitividad (Project: CGL2010-15726/BOS).

Sexually mature young males of many dichromatic species begin breeding while expressing female-like or incomplete adult phenotypes, which contradicts sexual selection theory. It is thought that by delaying the acquisition of adult appearance, young males may avoid aggression from other males, but reduce mating opportunities, resulting in trade-offs between these 2 life-history traits. Thus, an optimal young male phenotype should allow mating while reducing aggressiveness. Differential character maturation (i.e., the acquisition of adult appearance does not occur in all traits at the same time) has been described in bird species, but has largely been neglected in the study of delayed plumage maturation. Using the common kestrel Falco tinnunculus, we tested the prediction that maturation of different adult traits depends on the aggressiveness elicited by both male and female individuals and that young male phenotypes should be a combination of traits triggering low levels of aggressiveness while still revealing sex. We explored the pattern of delayed plumage maturation observed in 4 different adult male traits (head, rump, tail, and back plumages) in young breeding males captured over 8 years. We then analyzed the intensity of agonistic responses against these traits in breeding males and females by presenting young male decoys showing these mature characters. We found that those characters eliciting high aggressiveness in males (head and rump) were partly expressed in young males and only 1 (tail) of the 2 traits (tail and back) eliciting high aggressiveness in females was poorly expressed. Our study suggests that conspecific aggressiveness of both males and females can play a significant role in determining patterns of delayed plumage maturation.

BACKGROUND: Ecologically based rodent pest management using biological control has never been evaluated for vole plagues in Europe, although it has been successfully tested in other systems. The authors report on the first large-scale replicated experiment to study the usefulness of nest-box installation for increasing the breeding density of common kestrels (Falco tinnunculus) and barn owls (Tyto alba) as a potential biological control of common vole (Microtus arvalis) abundance in agricultural habitats in north-western Spain. RESULTS: The results show that: (1) population density of both predator species increased in response to both nest-site availability and vole density; (2) voles are a major prey for the common kestrels during the breeding period; (3) vole density during the increase phase of a population cycle may be reduced in crop fields near nest boxes. CONCLUSION: The installation of nest boxes provides nesting sites for barn owls and kestrels. Kestrel populations increased faster than in areas without artificial nests, and the common vole was one of their main prey during the breeding season. The results suggest that local (field) effects could be found in terms of reduced vole density. If so, this could be an environmentally friendly and cheap vole control technique to be considered on a larger scale. © 2012 Society of Chemical Industry

The simultaneous exhibition of more than one secondary sexual trait is a widespread phenomenon in nature, though it has rarely been explored. It has been proposed that different ornaments may convey complementary or back-up information about a single aspect of individual quality (redundancy hypothesis) or that each ornament may convey unique information (multiple-messages hypothesis). During a 5-year period, we measured several carotenoid-based (eye ring, bill cere and tarsi skin) and melanin-based (head, back, rump and tail feathers) potential ornamental colours in male common kestrels. We analysed whether multiple ornaments can convey different or related information about individual quality. We explored whether different ornaments can express different information depending on the pigment (carotenoids or melanins), the time-scale over which the ornament can change (dynamic vs. static) and the season of the year when the ornament is formed. We found that both melanin- and carotenoid- based traits correlated with indexes of quality, including body condition, body condition of their partners and laying date. However, not all ornaments correlated with the same measures of quality. In addition, some ornaments were intercorrelated within the same individuals while others were not. These results suggest that different ornaments can convey information about different qualities, as predicted by the multiple-messages hypothesis. In addition, this study suggests that the predominant pigment (e.g. carotenoid vs. melanin, eumelanin vs. pheomelanin), the time-scale over which the trait is developed (static feathers vs. dynamic skin) and the season of the year at which the ornament is produced can be potential mechanisms to convey different messages in male common kestrels.

Summary 1. Knowledge of how pathogens activate different components of the immune system to combat infections in the wild is a first step towards building a more global picture of the role that immunocompetence plays in host-parasite evolution and host life history. Ecological immunology is currently situated in this first step due, in part, to the scarcity of simple techniques to reliably evaluate immunocompetence in the field. In fact, controversy remains as to whether parasites act as immuno-stimulators promoting immune responses or as immune-depressors via immune resource depletion. 2. In this study we manipulated parasite infection (Caryospora, Protozoa, Apicomplexa) and vaccinated captive Eurasian kestrels (Falco tinnunculus) to study potential immunological responses in different components of the immune system: circulating lymphocyte lineages (CD4, CD5 and CD8), counts of total lymphocytes and white blood cells (WBC) and plasma immunoglobulins (α-1, α-2, β-1, β-2 and δ). 3. We also evaluated the efficacy of the PHA-assay, a common test used in ecological immunology, to gain information about T-cell-mediated immune response. 4. Experimentally infected and vaccinated (inoculated with attenuated parasites) birds showed drastic increases in CD4 and CD5 lymphocyte lineages, but not in CD8s, nor in total counts of lymphocytes or WBCs and no significant variation was observed in plasma globulins and in inflammatory reaction to PHA as a consequence of infection. PHA assay values were not correlated with initial (before vaccination) or final (after vaccination) values or with the response (final – initial) of T-lymphocyte lineages. 5. Individuals with initially lower numbers of CD4 showed higher numbers (higher immune response) after vaccination. In the case of CD5s, initial and final numbers were positively correlated. 6. This study shows that parasites clearly provoke immune activity stimulation through proliferation of T-lymphocytes (CD4 and CD5) and also reveals that other commonly used measurements, considered to be related to T-cell-mediated immunity, such as single-time-point measurements (total lymphocyte and WBC counts) or PHA assays, have a questionable capacity to provide information about immunological capacity to combat pathogens.

The duration of the postfledging dependence period (PFDP) is supposed to be modulated by the parent‐offspring conflict: Offspring should extract the highest levels of parental investment, although parents may respond by setting fixed limits to the level of investment or by raising the costs of attempts to extract additional investment. In this context, longer PFDPs are expected in nests tended by higher quality parents and in dominant siblings. We explored these hypotheses with a combination of experimental and correlative results. First, we food supplemented offspring during the PFDP to study whether food supply during fledging, an indicator of parental quality, has an effect on the PFDP duration in the Eurasian kestrel. We found that the PFDP was longer in food-supplemented nests. Second, we measured the duration of the PFDP over 3 years under different environmental conditions to explore whether the quality of parents and nestling phenotype were correlated with the duration of PFDP. Correlative results suggest that fledglings raised by higher quality parents and in the year with poorer food conditions showed longer PFDP. Furthermore, male fledglings showing grayer coloration in the rump (an index of competitive capacity) have longer PFDPs than browner males. Overall, our results suggest that parent, rather than offspring characteristics, can modulate the PFDP duration mediated by food conditions, although more colored nestlings stay in the nest territory for longer periods. Key words: environment conditions, Eurasian kestrel, Falco tinnunculus, melanic coloration, parent‐offspring conflict, sibling competition. [Behav Ecol]

Competition for resources (e.g. mates or food) is the main evolutionary explanation for conspicuous ornaments in males, although this idea is not generalized in females. Whether or not the expression of melanic coloration is dependent on environmental conditions remains controversial. We studied three different melanin-based female traits in the Eurasian kestrel Falco tinnunculus, a sexually dichromatic species, for a period of 10 years: grey coloration in rump and tail and the width of the black subterminal tail band. We analysed these traits for within-individual variation among years, as well as their possible link with indices of quality, such as age, body size, and breeding performance. The results obtained demonstrate that female melanin-based coloration increased from yearlings to adults. In addition, the expression of female rump coloration covaried positively with the environmental conditions in the previous year (i.e. measured as clutch size at population level). Finally, we found a positive correlation between grey rump coloration and clutch size. These results suggest that the expression of rump coloration, a melanin-based trait, is environmentally constrained, and we propose that this character could function as an indicator of individual quality in female Eurasian kestrels. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 781–790.

SUMMARY Mothers can strongly influence the development of their offspring, and if maternal resources are limited, they may influence optimal reproductive strategies. In birds, maternally deposited carotenoids are a prominent component of egg yolk and are vital for the development of the embryo. However, results of long-lasting fitness consequences of this early nutritional environment have been scarce and inconsistent. In addition,sex-biased sensitivity to different egg components is one of the mechanisms postulated to account for sex-linked environmental vulnerability during early life. However, this important aspect is usually not accounted for when investigating maternal investment in carotenoids. In this study we gave carotenoid (lutein) supplements to female Eurasian kestrels (Falco tinnunculus) before and during egg laying. The experiment increased female plasma carotenoids, but this effect was not apparent in hatchling and fledgling plasma carotenoid concentration. Also, results showed that carotenoid supplementation increased the high density lipoprotein to low density lipoprotein ratio in adult females, suggesting that dietary carotenoids may influence lipid metabolism. Furthermore, the effect of the treatment was manifested in several nestling health state parameters. Nestlings of carotenoid-supplemented females were infested by less intestinal parasite groups, had higher lymphocyte concentrations in blood plasma, and were less stressed (heterophile to lymphocyte ratio) than control nestlings. In addition, an interaction between the experimental treatment and nestling sex was apparent for globulin concentrations, favouring the smaller male nestlings. Thereby, suggesting that males benefited more than females from an increase in maternal carotenoid investment. Our study shows that an increase in carotenoids in the maternal diet during egg laying favours nestling development in kestrels, and may also affect nestlings in a sex-specific way.

Lesser kestrel Falco naumanni and Eurasian kestrel Falco tinnunculus are two small raptor species commonly breeding in open agro-pastoral systems that have suffered a dramatic decline in their populations during the past few decades due to changes in land use. Direct intoxication by chemicals used in farming has been one of the causes proposed promoting population declines in both species. However, there have been no studies exploring the degree of kestrel intoxication at individual or population levels in the wild. We investigated the inter-population variation in blood levels of acetylcholinesterase (AChE) in nestlings of Spanish Lesser and Eurasian kestrels. AChE was used as an estimator of the degree of organophosphorus (OP) and/or carbamate (CB) exposure or intoxication. In addition, we measured the albumin–globulin ratio (A/G) as an index of general health status. We found only extremely low AChE levels in lesser kestrels from one of the seven studied populations. In addition, we did not find differences in nestling AChE levels between pastoral and agricultural habitats. Furthermore, the present study revealed that two of the seven lesser kestrel populations are suffering from poor health conditions, in one case due to OP–CB poisoning, and the other possibly due to a pathogen infection as suggested by the low A/G ratio observed. Thus, our study suggests that, in general, OP and/or CB pesticide poisoning in traditional agro-pastoral systems in Spain is not currently an important conservation factor for either Lesser or Eurasian kestrels chicks.

Predation has received considerable theoretical and empirical support in population regulation. The effect of predators, however, could be achieved in direct (killing) or indirect effects (such as displacement). In this paper, we explored the relationship between Eurasian kestrels Falco tinnunculus and skylarks Alauda arvensis in Mediterranean grasslands. First, we analysed the presence of skylarks in the kestrel diet over 9 years. We also compared a grassland area of experimentally increased kestrel density and a second grassland as control area to evaluate the direct or indirect effect on skylark abundance. We also considered two different habitats, grazed and ungrazed plots. If skylark abundance decreased as the kestrel breeding season progressed in high-density kestrel area compared with the control area, it would suggest a direct effect (predator hypothesis). If skylark abundance remains constant in both areas of contrasting kestrel density, it would suggest that skylarks avoid kestrels (avoidance hypothesis). We found that skylark abundance decreased in the kestrel area from the beginning of kestrel nest-box installation to recent years. The rate of skylark consumption decreased in a 9-year period as kestrel abundance increased, although the total amount skylark consumption did not show a decreasing trend. In addition, skylarks were more abundant in the kestrel-free area than in the kestrel area. Finally, we found that skylark abundance did not change through the kestrel breeding period in relation to grazing. We suggest that an increased breeding density of kestrels during their breeding period may force the skylarks to breed in other areas, which may explain the decline of their abundance.

Success in sibling competition is one of the main factors determining individual body condition in the early stages of life and consequently offspring survival and fitness. In birds, most studies on this topic have been focused on the nesting period, but sibling competition still continues during the postfledging period. We studied sibling competition over 3 years during the postfledgling dependence period in the Eurasian kestrel Falco tinnunculus, a reversed sexually size dimorphic species. Contrary to that in the nesting stage, male fledglings showed a higher competitive capacity than females resulting from their greater success in capturing larger prey items delivered by parents. Furthermore, male fledglings showing grayer coloration in the rump captured greater number of larger prey than browner males. Our results suggest that patterns of sibling competition in nestlings can differ from those found during postfledging, revealing the importance of studying this period in order to achieve a more complete view of sibling competition. In addition, kestrel fledglings with grayer rumps were more likely to have larger prey items, suggesting that this character can be interpreted as a phenotypic indicator of quality. Key words: brood hierarchies, Falco tinnunculus, hatching order, prey delivery, sex differences, status signaling. [Behav Ecol]

Aggressive behaviour against conspecifics is considered a costly behaviour that forms part of reproductive investment. Previous studies have suggested that the intensity of agonistic behaviour may indicate individual quality since it exhibits a positive correlation with brood value. However, this relationship has been demonstrated after clutch completion, and by creating a nexus between efforts it has not been possible to disentangle other hypotheses that could explain such findings. Here, by presenting a trio of natural decoys (adult male, adult female and 1-year-old male) to Eurasian kestrels, Falco tinnunculus, we tested whether the aggressive behaviour to conspecifics prior to laying predicted posterior reproductive performance (clutch size). We also tested the effect of breeding stage and breeding density on this behaviour. In addition, we examined the effect of the presence of moulted versus unmoulted 1-year-old males on aggressive behaviour of breeders. Intrasexual agonistic behaviour, measured as attack intensity to the decoys, was positively correlated with clutch size in females, but negatively in males. In males, aggressive behaviour was lower during the female fertile stage than during previous stage, but in females, was similar over stages. Furthermore, agonistic behaviour increased with breeding density in females but not in males. We discuss these results in the context of sexual selection theory, and propose that the link between agonistic behaviour prior to laying and clutch size is via the connection to courtship feeding and that may be considered as an indicator of individual quality for both sexes.

Delayed plumage maturation (DPM) of young males in sexually dichromatic birds has been explained under the female mimicry hypothesis (FMH) or the subordination signalling hypothesis (SbSH), among other adaptive ideas proposed. In this study, we tested in the Eurasian kestrel, Falco tinnunculus, the predicted sexual deception and aggressiveness under the FMH and SbSH to explain DPM in birds. We analysed aggressive and courtship behaviour of breeding males and females in the presence of adult male, adult female and 1-year-old male natural decoys. We designed two different treatments: one presenting un-moulted 1-year-old males and a second presenting partly moulted 1-year-old males, as observed in nature. Males attacked adult male decoys more frequently than 1-year-old male and female decoys in both moulted and un-moulted treatments and no sexual displays were observed. Females were more aggressive towards female and 1-year-old male decoys as compared to male decoys in the un-moulted treatment. In the moulted treatment, females were more aggressive towards female decoys as compared to both male decoys. In addition, females solicited copulas from moulted, but not from un-moulted, 1-year-old male decoys. Our results suggest that FMH can be a mechanism which explains DPM in un-moulted 1-year-old males. However, when they show moulted plumage (more than 80% in the studied population during the spring), the SbSH seems to be the mechanism that better explains sexual and agonistic behaviour from adults towards 1-year-old males.

The theory of sex allocation suggests that if the reproductive value and the cost of producing/rearing offspring differ between male and female offspring, parents should invest differently in sexes depending on environmental conditions. Female parents could allocate more resources to eggs of one sex to compensate potential sex-dependent constraints later during the nestling period. In this study, we tested the influence of environmental conditions on sexual dimorphism in eggs of Eurasian kestrels (Falco tinnunculus) by experimentally manipulating food availability before laying. We found that an increase in food abundance before laying did not increase egg mass but changed sex-dependent resource distribution in eggs. In food-supplemented pairs, but not in control pairs, egg mass and hatchling mass were similar between males and females. In addition, we found, in the food-supplemented group, that the latest hatched females showed shorter hatching times than in the control group. In control pairs, female eggs, hatchlings and nestlings were heavier than males. In addition, male fledglings in the food-supplemented group gained less mass than those in the control group. As that food abundance was only increased until the onset of laying, female kestrels were expected to invest in eggs taking food abundance before egg formation as a predictor of future conditions during brood rearing. Our study shows that environmental conditions before laying promote a subtle adjustment of the resources invested in both sexes of offspring rather than in other breeding parameters. This adjustment resulted in a shortening of hatching time of the last hatched females that possibly gives them advantages in their competitive capacity with respect to male nest-mates.

Secondary sexual traits displayed by males and females may have evolved as a signal of individual quality. However, both individual quality and investment on producing or maintaining enhanced sexual traits change as individuals age. At the same time, the costs associated to produce sexual traits might be attenuated or increased if environmental conditions are benign or worse respectively. Accordingly, environmental conditions are expected to shape the association between the expression of sexual traits and their reproductive outcome as individuals age. Nonetheless, little is known about the environmental influence on the co-variation between sexual traits and reproductive outcome throughout the life of individuals. We studied the age-dependency of the number and size of back spots, a melanin-based and sexual trait in adults of common kestrels (Falco tinnunculus). We analysed the age-dependence of reproductive traits and the environmental influence, defined as vole abundance, using a 10-year individual-based dataset. We broke down age-related changes of reproductive traits into within- and between-individual variation to assess their contribution to population-level patterns. Our results showed a within-individual decrease in the number, but not the size, of back spots in males. The size of back spots was positively correlated with food availability in males. Reproductive performance of males increased as they aged, in agreement with the life-history theory but depending of vole abundance. Remarkably, we found that having fewer back spots was positively associated with clutch size only for old individuals under low-food conditions. We suggest that environmental variation may shape the association between the expression of a sexual signal and reproductive outcome. We speculate that the reliability of sexual traits is higher when environmental conditions are poor only for old individuals. Within an evolutionary context, we suggest that the expression of sexual traits might be constrained by environmental conditions at later stages of life., The long-term monitoring of the study population was financed by several projects of the Ministerio de Economía y Competitividad (CGL2004-04479/BOS, CGL2007-61395/BOS, CGL2010-15726/BOS, CGL2013-42451-P) of the Spanish Government.

© 2015 Navarro-López, Fargallo. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Recent research reports that many populations of species showing a wide trophic niche (generalists) are made up of both generalist individuals and individuals with a narrow trophic niche (specialists), suggesting trophic specializations at an individual level. If true, foraging strategies should be associated with individual quality and fitness. Optimal foraging theory predicts that individuals will select the most favourable habitats for feeding. In addition, the >landscape heterogeneity hypothesis> predicts a higher number of species in more diverse landscapes. Thus, it can be predicted that individuals with a wider realized trophic niche should have foraging territories with greater habitat diversity, suggesting that foraging strategies, territory quality and habitat diversity are inter-correlated. This was tested for a population of common kestrels Falco tinnunculus. Diet diversity, territory occupancy (as a measure of territory quality) and habitat diversity of territories were measured over an 8-year period. Our results show that: 1) territory quality was quadratically correlated with habitat diversity, with the best territories being the least and most diverse; 2) diet diversity was not correlated with territory quality; and 3) diet diversity was negatively correlated with landscape heterogeneity. Our study suggests that niche generalist foraging strategies are based on an active search for different prey species within or between habitats rather than on the selection of territories with high habitat diversity., This work was supported by Project of Ministerio de economía y competitividad (MIMECO) CGL2007-61395 and Project of Ministerio de economía y competitividad (MIMECO) CGL2010-15726 (http://www.mineco.gob.es/). JNL was supported by a fellowship of Ministerio de economía y competitividad (MIMECO) BES-2011-043956 (http://www.mineco.gob.es/).

Melanin pigments are responsible for most non-structural brown, black and grey colouration in animals. The extent to which melanin-based colouration in birds is genetically or environmentally determined has been subject to controversy. One reason for this it is paucity of empirical data on the role of key environmental factors, such as food availability, on the development of melanin-based traits. We analysed whether brown and grey colouration in rumps of Eurasian kestrels Falco tinnunculus is based on melanin and examined the relationships between high inter- annual variation in main food supply, parental condition and the expression of grey colouration in male nestlings. We also performed a partial cross-fostering experi- ment to allocate randomly nestlings among environments. The proportion of male nestlings with predominantly grey colouration was higher in years with abundant prey (voles). The only variable associated with intra-annual variation of grey col- ouration in male nestlings was body mass of the female rearing them. The colour- ation of nestlings in the cross-foster experiment was correlated with the body mass of their foster mother, but not with that of their genetic mother. Melanin colouration did not correlate with T-cell mediated immune response. These results indicate that this melanin-based trait reflects the environmental conditions in which the nestlings grew up.

Nest-site fidelity is a life-history trait of birds that may produce benefits in terms of fitness. We studied the relationship between breeding success and nest fidelity in the White Stork Ciconia ciconia. We also studied how other factors such as age, sex, habitat, colony size and productivity in previous breeding attempts might interfere with this relationship. Our results showed that pairs with higher fidelity rates also have lower failure rates, and that breeding failure and productivity in the previous season influenced the frequency of nest change in the following season. In addition, a curvilinear relationship was found between age and nest fidelity. These results suggest that age is a major factor related to nest fidelity and therefore individual experience could explain this behaviour in the White Stork. Changing the nest involves a reproductive cost for which nest fidelity can be considered as an adaptive strategy to increase fitness.

We investigated how the expression of carotenoid-based plumage coloration (lightness and chroma) in nestling blue tits Parus caeruleus is associated with forest structure in oak forests of central Spain. We found evidence of a reduced expression of carotenoid-based coloration in nestlings growing up in successionally young and structurally simple forest territories. Our results suggest that breast feather coloration can be used as an indicator of nestling quality because nestlings with more intense yellow plumage coloration had larger body size and stronger immune responses to the injection of phytohemagglutinin (PHA). Given the association of forest structural complexity with carotenoid-based plumage coloration, our findings suggest that variation in habitat structure may have a significant impact on forest birds in their first stages of life which has implications for forest management practices.

Human disturbance can be considered to have similar effects as predation risk for animals. Thus, when disturbed, animal responses are likely to follow the same economic principles used by prey when encountering predators. We simulated predator attacks with different characteristics and in different situations to study the factors that determine the escape response of 1-year-old chinstrap penguins. The results indicate that 1-year-old penguins adjusted their escape behaviour according to the level of risk posed by the researcher acting as a potential predator. When 1-year-old penguins were close to a breeding subcolony, they started to escape later, and fled shorter distances, at lower speeds, and not fleeing directly into the subcolony. This contrasts with their fleeing behaviour far from subcolonies, when penguins fled sooner, for longer, and faster, and in a direction that maximized the distance between themselves and the experimenter, by fleeing directly away from the experimenter. This might suggest the existence of a trade-off between fleeing from the predator and avoiding entering the subcolony where 1-year-old penguins will receive aggressive responses from breeding adults. The type of approach was not important in deciding when to flee. However, penguins did escape for longer distances and faster when approached directly, showing that penguins were able to assess risk level based on predator behaviour. Our findings may have implications for management of penguin colonies visited by tourists. The delimitation of buffer areas and advice on how tourists should behave when approaching penguins might arise from studies of the factors that affect risk assessment of penguins.

Summary 1 Offspring sex ratio may be an unpredictable component of life history that might select for behavioural plasticity in parental care. If the parents do not have such plasticity and the two sexes of offspring differ in size, individuals in a brood or litter biased towards the larger sex offspring may suffer from food shortage. Sibling sex ratio could also affect the young through asymmetric sex-related sibling competition. 2 We created single-sex broods of sexually size-dimorphic Eurasian kestrels (Falco tinnunculus L.) with mixed-sex control broods in order to test whether parents have behavioural plasticity to respond to the sex ratio of their brood and whether smaller male chicks suffer from reduced health status because their larger female siblings outrival them in sibling competition. The experiment was conducted during two years (2000 and 2001) that differed in the abundance of voles, the main natural prey of kestrels. 3 No obvious effects of the brood sex ratio manipulation on parental effort were detected, as there were no differences in prey delivery rate, biomass of prey brought to the nest, body mass or heterophile/lymphocyte ratio of the parents. 4 Female chicks in all-female broods had lower haematocrit levels than those in mixed-sex broods in a year of low vole abundance. As haematocrit is an index of nutritional condition and health state, this result indicates that in the year of low vole abundance the female chicks in all-female broods fledged in poorer condition than those in mixed-sex broods. 5 These results indicate that when the parents do not alter their level of parental effort in response to the sex ratio of their brood, the young in a brood biased towards the larger sex offspring can be reared successfully when food is abundant, while they may suffer under food shortage situations. 6 Kestrel chicks of both sexes had low haematocrit levels and T cell-mediated immune responses in the year of low vole abundance. This result indicates that poor health state at fledging may provide a causal link for low recruitment of kestrels hatched in years of low vole abundance.

Variation in the sex ratio at hatching in the chinstrap penguin Pygoscelis antarctica was investigated, using molecular sexing to test predictions of sex allocation theory. The sex ratio was slightly male-biased (0.54) but did not differ significantly from parity. The proportion of males increased with nest size, an estimator of parental quality in chinstrap penguins. High-quality parents were able to produce and rear a higher proportion of male offspring, the more costly sex in this slightly sexually dimorphic species. Our results may be in agreement with Trivers and Willard's (1973) argument on biases in the offspring sex ratio being contingent on parental condition or quality. © Springer-Verlag 2004.

Diseases have been recently suggested as a potential cost that parents and offspring pay for an elevated reproductive effort in wild organisms. We investigated the relationship between clutch size ...

When resources are limited, parents should decide the optimal number, size, and sex of progeny, and offspring should decide the optimal allocation of resources to different costly functions, such as growth and immunity. We manipulated clutch sizes of Eurasian kestrels by one egg to estimate possible cumulative effects of incubation and chick rearing costs on parental body condition, feeding effort, and offspring viability. No obvious effects of clutch size manipulations on feeding effort were found while feeding effort was adjusted to the original clutch size. Enlarged and control nests suffered from higher nestling mortality than reduced nests, and chicks of the enlarged group were in poorer body condition than chicks of the reduced group. Controlling for body mass, male chicks exhibited lower cell-mediated immunity assessed by a cutaneous hypersensitivity response than females, but only in treatments suffering from food restrictions, as indicated by chick starvation. These novel results reveal inter-sexual differences in physiological strategies in early life, suggesting sex-related differences in susceptibility to disease and consequently in survival prospects of offspring.

Infectious diseases and parasitism are major environmental forces decreasing fitness, and thus individual strategies aimed at preventing pathogen infections, either in an individual or their offspring, should be favoured by natural selection. The mineral fraction and some organic compounds in the shells of bird eggs are considered physical and chemical barriers against pathogen penetration to the embryo. However, eggshell pigment deposition has only recently been considered as a mechanism to resist pathogen penetration into the egg. By wiping the eggshell surface, the amount of pigment and some cuticle proteins were experimentally manipulated for the first time in nature. The effects on egg hatchability and offspring viability measured as nestling condition, immunocompetence and probability of recruitment were investigated in the common kestrel Falco tinnunculus. Protoporphyrin IX and biliverdin IXα to a lesser extent were the only identified pigments. The concentration of protoporphyrin IX and cuticle proteins were significantly reduced in the wiped with respect to the control treatment. Our study shows no evidence of a detrimental effect of the reduction of eggshell pigments on egg hatchability, mortality of the chicks during the nesting period, nestling body condition, nestling local immune response to PHA antigen or probability of recruitment. Further research will be necessary to elucidate the direct role of protoporphyrins and other pigments in egg bacterial infection. © 2014 Springer International Publishing Switzerland., The Spanish Ministry of Science and Innovation (Projects: CGL2007-61395/BOS and CGL2010-15726/BOS) approved the experimental design and financed the study.

Stone provisioning is a nest-maintenance activity accomplished by pygoscelid penguins after reliefs during the incubation/brooding period. The functional significance of this behaviour has been mainly explained as a parental strategy preventing nest flooding under detrimental weather conditions. In addition, and in the light of recent studies, this behaviour could also fit into the sexual selection process. In this study, we tested the first idea, that is, whether stone provisioning is a nest-maintenance behaviour to increase egg/nestling survival by lowering the risk of nest flooding, and can thus be considered a form of parental care. Additionally, we investigated if the effort invested by parents in nest maintenance is constrained by physiologically limiting resources. The effort of stone collection and the perceived risk of nest flooding were experimentally manipulated during the incubation and early brooding phases in a chinstrap penguin, Pygoscelis antarctica, colony. Three groups of nests were established. After weighing, control nests were left unmanipulated. In a second group of nests (reduced group), only one-half of the initial weight of stones was returned to the nests. In a third group of nests (snow-added group), we both reduced nest weight by a half and added snow outside the nest bowl over 6 consecutive days. Ten days after manipulation, the difference in nest weight between initial and final conditions was significantly related to treatment: penguins increased stone provisioning in the reduced group (44% of half-reduced nests), but drastically more in the reduced and snow-added group (123% of half-reduced nests), while the weight of control nests was unchanged compared to premanipulation conditions. The intensity of stone provisioning was affected by nest date, peaking about hatching time and shortly after, and declining with advancing chick age. These results suggest that stone provisioning is a mechanism that has evolved to prevent egg or chick mortality by nest flooding. The haematocrit, but not leukocyte numbers as expressed by the buffy coat layer, varied with the experimental conditions. Penguins investing more time in nest maintenance had a lower haematocrit, suggesting a physiological trade-off probably mediated by competition between the time devoted to nest maintenance versus foraging activities. The amount of stones collected and the haematocrit were positively related to the number of neighbour nests, so those individuals surrounded by more nests seemed to obtain benefits in the availability of nest material and energy savings. This study indicates that stone-provisioning behaviour is a nest-maintenance activity evolved to improve thermal nest characteristics potentially increasing offspring survival, and competing in time and energy with other reproductive activities. Stone provisioning in penguins should therefore be regarded as a form of parental care and an important part of individual reproductive effort in species breeding in harsh environments. Furthermore, nest size and nest-maintenance effort should be considered reproductive traits indicative of parental quality and thus could also be involved in the post-mating sexual selection process.

We analysed genetic relatedness through DNA-fingerprinting in 38 two-chick families of Chinstrap Penguins Pygoscelis antarctica in the Vapour Col colony on Deception Island, Antarctica. Band-sharing coefficients between males and chicks in their nests, females and chicks in their nests and brood mates were very close to 0.50 and were not significantly different. Presumably unrelated pair mates showed much lower band-sharing coefficients (0.12), which differed significantly from those between putative parents and their chicks and between presumed siblings. No case of extra-pair paternity was detected according to the presence of novel bands or to band-sharing coefficients. Monogamy in the study population is not only social but also genetic.

Health status and immunocompetence have been proposed as important factors affecting individual variation in the attainment of breeding condition in birds. We studied individual variation in serological variables indicating health status (blood sedimentation rate, haematocrit, `buffy coat' layer, proportions of different types of leucocytes) in two groups of breeding chinstrap penguins Pygoscelis antarctica with breeding dates 9 days apart. We sampled these individuals shortly after hatching of their young and at the end of the chick-raising period. A group of failed breeders was also sampled. Birds of both sexes were included. We also measured the T-cell-mediated immune response as indicated by an in vivo hypersensitivity response to an intradermal injection of a mitogen (phytohaemagglutinin) in early and late breeders. Sex had no significant effect on most variables. Late breeders had poorer health (more leucocytes, especially heterophils and lymphocytes) and a lower T-cell-mediated immune response than early breeders. Failed breeders were more similar to late than to early breeders. Early breeders suffered a decline in health status throughout the chick-raising period. The impact of pathogens on variation in life history traits in avian populations may be important even in extreme Antarctic environments.