Search

Sociality impacts many biological processes and can be tightly linked to an individuals fitness. To maximize the advantages of group living, many social animals prefer to associate with individuals that provide the most benefits, such as kin, familiar individuals, or those of similar phenotypes. Such social strategies are not necessarily stable over time but can vary with changing selection pressures. In particular, young individuals transitioning to independence should continuously adjust their social behavior in light of developmental changes. However, social strategies exhibited during adolescence in animals are understudied, and the factors underlying social network formation during ontogeny remain elusive. Here, we tracked associations of wild great tits (Parus major) during the transition to independence and across their first year of life. Both spatial and social factors predicted dyadic associations. During the transition to independence in spring, fledglings initially preferred to associate with siblings and peers over non-parent adults. We found no evidence for preferred associations among juveniles of similar age or fledge weight during that time but weak evidence for some potential inheritance of the parental social network. By autumn, after juveniles had reached full independence, they exhibited social strategies similar to those of adults by establishing stable social ties based on familiarity that persisted through winter into the next spring. Overall, this research demonstrates dynamic changes in social networks during ontogeny in a species with a fast life history and limited parental care, which likely reflect changes in selective pressures. It further highlights the importance of long-term social bonds based on familiarity in this species.

Empirical studies from laboratory systems and humans show that the gut microbiota is linked to host health. Similar evidence for effects on traits linked to fitness in nature is rare, not least because experimentally manipulating the gut microbiota is challenging. We isolated, characterized, and cultured a bacterial strain, Lactobacillus kimchicus APC4233, directly from a wild bird (the great tit Parus major) and provided it as a self-administered dietary supplement. We assessed the impact of the treatment on the host microbiota community, on weight, and tested whether the treatment affected a previous result linking microbiota alpha diversity to weight in nestlings. The treatment dramatically increased L. kimchicus abundance in the gut microbiota and increased alpha diversity. This effect was strongest in the youngest birds, validating earlier findings pointing to a brief developmental window when the gut microbiota are most sensitive. In time-lagged models, nestling weight was higher in the treatment birds suggesting L. kimchicus may have probiotic potential. There was also a positive time-lagged relationship between diversity and weight in control birds but not in the treatment birds, suggesting L. kimchicus helped birds compensate for low alpha diversity. We discuss why ecological context is likely key when predicting impacts of the microbiome. The manipulation of the gut microbiota with a host native strain in this wild population provides direct evidence for the role of the microbiota in the ecology and evolution of natural populations. [ABSTRACT FROM AUTHOR]

Urbanization forms one of the most drastic alterations of the environment and poses a major threat to wildlife. The human–induced modifications of the landscape may affect individual's fitness resulting in population declines. Research on how urbanization affects fitness traits has shown mixed results. However, studies typically contrasted data from a single species from few urban and non‐urban sites collected over short timeframes. Examining multiple species across a broad urbanization gradient enables a more robust comparison and understanding of how different species are impacted by urbanization‐knowledge crucial for generating population predictions, which are essential for conservation management. Here, we use data from a nation‐wide citizen science project to examine variation in survival and relative body mass and size (wing length) of common passerine birds, collected along an urbanization gradient in the Netherlands over an 8‐year period. Urbanization was measured as the distance from the city's border and the proportion of impervious surface area. Although the overall association between urbanization and survival was slightly negative, there was support for lower survival closer to the city in three species (chiffchaff Phylloscopus collybita, European robin Erithacus rubecula, European greenfinch Chloris chloris) and higher survival closer to the city in two (great tit Parus major and house sparrow Passer domesticus) of the 11 species examined. The contrasting survival successes among species suggest that ongoing urbanization may lead to shifts in community structure and loss of biodiversity. Impacts of urbanization on relative mass and size also exhibited varying effects, albeit less pronounced, and these effects were not correlated with the effects on survival. This implies that body mass and size cannot be used as indicators for urban‐associated patterns of survival. Our results further imply that effective conservation management targeting bird communities should involve a range of diverse actions, as focusing on single measures is unlikely to simultaneously impact multiple species due to the variation in responses to urbanization. [ABSTRACT FROM AUTHOR]

Circadian clock properties vary between individuals and relate to variation in entrained timing in captivity. How this variation translates into behavioural differences in natural settings, however, is poorly understood. Here, we tested in great tits whether variation in the free‐running period length (tau) under constant dim light (LL) was linked to the phase angle of the entrained rhythm ("chronotype") in captivity and in the wild, as recently indicated in our study species. We also assessed links between tau and the timing of first activity onset and offset under LL relative to the last experienced light–dark (LD) cycle. We kept 66 great tits, caught in two winters, in LL for 14 days and subsequently released them with a radio transmitter back to the wild, where their activity and body temperature rhythms were tracked for 1 to 22 days. For a subset of birds, chronotype was also recorded in the lab before release. Neither wild nor lab chronotypes were related to tau. We also found no correlation between lab and wild chronotypes. However, the first onset in LL had a positive relationship with tau, but only in males. Our results demonstrate that links between tau and phase of entrainment, postulated on theoretical grounds, may not consistently hold under natural conditions, possibly due to strong masking. This calls for more holistic research on how the many components of the circadian system interact with the environment to shape timing in the wild. Wild birds showed chronotypes in the field that were unlinked to their circadian period length tau measured in captivity. In males only, the first onset of activity after exposure to constant dim light did correlate with tau. Our study emphasises the need to investigate clocks in the real world, including a need to better understand masking. [ABSTRACT FROM AUTHOR]

Environmental variation can shape the gut microbiome, but broad/large‐scale data on among and within‐population heterogeneity in the gut microbiome and the associated environmental factors of wild populations is lacking. Furthermore, previous studies have limited taxonomical coverage, and knowledge about wild avian gut microbiomes is still scarce.We investigated large‐scale environmental variation in the gut microbiome of wild adult great tits across the species' European distribution range. We collected fecal samples to represent the gut microbiome and used the 16S rRNA gene sequencing to characterize the bacterial gut microbiome.Our results show that gut microbiome diversity is higher during winter and that there are compositional differences between winter and summer gut microbiomes. During winter, individuals inhabiting mixed forest habitat show higher gut microbiome diversity, whereas there was no similar association during summer. Also, temperature was found to be a small contributor to compositional differences in the gut microbiome. We did not find significant differences in the gut microbiome among populations, nor any association between latitude, rainfall and the gut microbiome.The results suggest that there is a seasonal change in wild avian gut microbiomes, but that there are still many unknown factors that shape the gut microbiome of wild bird populations. [ABSTRACT FROM AUTHOR]

The frequency of extreme climatic and weather events has increased since 1950 due to global changes induced by human influence. These events can have significant impacts at the individual, population, and community levels across various taxonomic groups. They can be particularly detrimental to bird populations during their breeding season, affecting specific breeding parameters. This study originated from an exceptionally rare breeding season of a resident Great Tit population recorded in spring 2002 when an unusual mortality of nestlings was observed. We quantified weather conditions (temperature, rainfall) from the end of April, a few days before we started detecting failed nests, and compared them with previous and subsequent years. In early May, when many pairs were incubating or caring for newly hatched chicks, we detected unusually low ambient temperatures and unusually high rainfall. This event likely caused that many first clutches failed completely, and that, compared with previous and subsequent years, fledging and breeding success was relatively low in those which were successful. There was also an increased proportion of replacement clutches that year. Anyway, the overall production of fledglings per breeding pair over the breeding season was 2.39, lower than other years. Although recruitment rate in 2003 was similar to other years, the lower production of fledglings in 2002 probably resulted in a decrease in the number of breeding pairs in the following years. [ABSTRACT FROM AUTHOR]

Recent research on bird calls has unearthed a striking result: birds sometimes react to the calls of other species that are neither geographically nor phylogenetically close. One mechanism explaining this response may be the recognition of specific acoustic features, also present in their own vocalizations, rather than the recognition of complete notes, with the result that unfamiliar calls may be understood if they contain the critical feature. Parids and other passerines produce mobbing calls with similar properties that are responded to across species (i.e. noisy, large frequency range notes reaching low frequencies and with numerous harmonics) that are therefore good candidates for recognition based on features. In a playback experiment, we explored the featural interpretation hypothesis by testing the response of free-ranging great tits, Parus major , to artificial mobbing calls with varying acoustic properties. We first confirmed that they respond to artificial calls sharing all the targeted spectral properties (large frequency range, low frequency, noise and harmonics). In contrast, great tits did not respond to calls with the same rhythmicity but without the targeted features. We then tested whether great tits respond to calls that possess only one of the four above-mentioned properties. We show that great tits did not respond to any of the four treatments, and therefore no single specific spectral feature seems likely to explain great tits' response to unknown calls. We discuss alternative mechanisms for decoding novel calls, notably through a similarity threshold. • How do birds recognize relevant mobbing calls? • One hypothesis is that they focus on specific acoustic features, not whole notes. • Great tits respond to artificial mobbing calls that have four crucial features. • Great tits do not respond to mobbing calls with only one feature. • More sophisticated hypotheses, beyond simple featural decoding, are posited. [ABSTRACT FROM AUTHOR]

A growing number of studies suggest that individuals can develop long‐term foraging specializations independently of phenotypic or environmental variation, yet little is known about how the foraging niche is acquired. The early learning of the foraging niche hypothesis suggests a key role of vertical cultural transmission in shaping the foraging niche of vertebrates. In birds, direct evidence from natural conditions is limited to a single study that cross‐fostered two related species. To date, no study has tested whether the diet received as an offspring determines the diet delivered as a parent within a single species. We tested the early learning of the foraging niche hypothesis using a Mediterranean population of great tits Parus major, which show great diet variability and moderate consistency in the diet they provide to their offspring across years. To do this, we recorded prey delivered to 9–14 day‐old chicks over twelve years. Then we assessed vertical transmission of dietary specialization using data (percentage of caterpillars, spiders, and other prey types, as well as mean prey size) from individuals recorded as a chick and as an adult. We standardised the data to control for environmental factors and ran a Linear Model for each prey type to measure individuals' consistency within the group (relative consistency), correlating the diet they received as a chick and the one they provided to their own chicks at the adult stage. The correlations between the diet received as a chick and the diet provided as a parent were either not significant or negative. Hence, although individuals showed relatively consistent foraging niches across years regarding their parental provisioning behaviour, these diet preferences were not correlated to the diet they received in the nest. Further research is needed to determine whether the foraging niche is acquired during the post‐fledgling stage. [ABSTRACT FROM AUTHOR]

Urbanisation has been increasing worldwide in recent decades, driving environmental change and exerting novel selective pressures on wildlife. Phenotypic differences between urban and rural individuals have been widely documented in several taxa. However, the extent to which urbanisation impacts mating strategies is less known. Here, we investigated extra‐pair paternity variation in great tits (Parus major) and blue tits (Cyanistes caeruleus) breeding in nestboxes set in a gradient of urbanisation in Warsaw, Poland, over three breeding seasons. Urbanisation was quantified as the amount of light pollution, noise pollution, impervious surface area (ISA) and tree cover within a 100‐m radius around each nestbox. We obtained genotypes for 1213 great tits at 7344 SNP markers and for 1299 blue tits at 9366 SNP markers with a genotyping‐by‐sequencing method, and inferred extra‐pair paternity by computing a genomewide relatedness matrix. We report higher extra‐pair paternity in blue tits breeding in more urbanised areas, for example, with higher light pollution and ISA, and lower tree cover. However, no such trend was found in great tits. Late‐stage survival of individual nestlings in both species was not associated with paternity or urbanisation proxies, thus we were not able to detect fitness benefits or drawbacks of being an extra‐pair offspring in relation to urbanisation. Our results contribute to the growing body of knowledge reporting on the effects of urbanisation on avian ecology and behaviour, and confirm species‐specific and population‐specific patterns of extra‐pair paternity variation. [ABSTRACT FROM AUTHOR]

Human-induced disturbance is perceived by avian species as a predation risk. However, the anti-predatory behaviour triggered by these non-lethal events can have negative impacts on reproduction and offspring survival. Research on breeding birds often involves visits to their nests and is likely to disrupt parental behaviour, but nest visits that do not involve direct handling of females have been overlooked as important disturbance events. This study focuses on the impacts of short visits to the nest of incubating Great tit (Parus major) females. We investigated how long they stay away from the nest (off-bout) after a disturbance, their possible compensatory behaviour once they resume incubation (on-bout), and the effects on daily incubation rhythms. We used three years of data from two breeding populations to assess the consequences of disturbances in two scenarios: when the female is present in the nest and flushed, and when the female is absent. We found that after a disturbance, the immediate off-bout was longer when the female was either present or absent, with the magnitude of the disturbance being greater when females were flushed. Females did not compensate with longer on-bouts afterwards, i.e. the research disturbance altered daily incubation behaviour by reducing the total time spent on the nest in relation to the number of daily disturbance events. Females that alter their behaviour in response to perceived predation risk would perform longer incubation periods, resulting in lower hatching rates. These effects of research on female behaviour should be considered when planning field experiments. Significance statement: Incubating birds react to human activity near their nests by changing their behaviour. This may also apply to basic research activities, but we have no data on how a visit, e.g., to check clutch size, affects them. To find out, we classified data from routine research visits to great tit nests, which are often used for research in the wild, into long and short visits. We also considered whether a female was incubating or foraging outside the nest during the visit. We found that females tended to stay away from the nest longer after they encounter a researcher, and after longer visits. Our results show that even slight research activities in the nest alters female incubation behaviour. They flee and leave the clutch unattended for longer, changing the thermal environment of the nest, which is crucial for proper embryo development. [ABSTRACT FROM AUTHOR]

Due to the limited number of field studies investigating associations between environmentally relevant per- and polyfluoroalkyl substances (PFAS) mixtures and reproductive impairment, there is uncertainty as to whether birds are affected by PFAS pollution, whether species differ in sensitivity to PFAS, and whether the observed reproductive impairment is caused by PFAS or rather due to other potential confounding variables. Therefore, we investigated PFAS concentrations in eggs and blood plasma of great tit (Parus major) and blue tit (Cyanistes caeruleus) nestlings near a PFAS hotspot in Belgium, reproductive impairment, and associations between the accumulated levels and nestling body condition. In total, 29 eggs and 22 blood plasma samples of great tit clutches, and 10 egg and 10 blood plasma samples of blue tit clutches, were collected. Despite more types of PFAS being detected in eggs compared to plasma, only minor differences in profiles were observed between species. On the other hand, tissue-specific differences were more pronounced and likely reflect a combination of maternal transfer and dietary exposure post-hatching. Despite the high concentrations detected in both species, limited reproductive impairment was observed. Our results support previous findings that great tits and blue tits may not be very susceptible to PFAS pollution and provide evidence that other factors, including ecological stoichiometry, may be more important in explaining inter-species variation in PFAS accumulation and reproductive impairment. [ABSTRACT FROM AUTHOR]

Most animals live and move in a landscape in which the risk of predation varies spatially and temporally, that is, a “landscape of fear” which may strongly affect their ecology and behaviour. Cavity‐nesting birds prospecting for nest sites are often forced to investigate unfamiliar, dark holes that may be dangerous to enter because they may conceal an aggressive nesting bird or a predator. The Fear of Feathers Hypothesis posits that some birds such as blue tits Cyanistes caeruleus, add large, conspicuous feathers on top of their own nest to exploit the fear of potential nest usurpers or brood parasites. Feathers may trigger fear in prospecting birds either because the feathers obstruct the view of the cavity interior, and/or because the feathers may be perceived as recent prey remains and suggest the predator will return. Here I studied the prospecting behaviour of unmated male pied flycatchers Ficedula hypoleuca by letting them choose between a dyad of nest boxes where one contained a nest of a great tit Parus major and one a nest of a blue tit. The objective was to test whether the presence of feathers would have a stronger repelling effect than the species that had built the nest. Great tits are larger than blue tits and may represent a greater threat to intruding flycatchers. However, blue tits but not great tits, often decorate their nest with large, conspicuous feathers. Consistent with the Fear of Feathers Hypothesis, flycatchers hesitated longer to enter blue tit than great tit nests but only if the blue tit nest contained feathers. The study has relevance to many species of birds that decorate their nest with feathers. It shows that a landscape may include aspects of fear that are important to animal behaviour although they may seem subtle and are easily overlooked. [ABSTRACT FROM AUTHOR]

Behavioural traits are under both genetic and environmental influence during early life stages. Early environmental conditions related to the amount and type of food have been found to alter behaviour in many organisms. However, how early life diet affects the variation in and the correlation between behavioural traits is largely unknown. Using a multivariate approach, we investigated how variation in parental prey selection is related to three repeatable nestling personality traits, and explored the within and between‐individual covariation between these behaviours in a wild passerine, the great tit (Parus major). Our results confirm that breath rate, docility and handling aggression (HA) in great tit nestlings are repeatable traits. Contrary to our expectation, the three nestling personality traits did not form a behavioural 'syndrome' on the phenotypic level in the study population, but we found two of three expected phenotypic correlations, mostly at the within‐individual level. Moreover, we found that breath rate significantly decreased with a higher number of spiders in the diet, and docility and handling aggression were significantly and inversely related to higher numbers of noctuids and tortricids in the diets of individuals within broods. Thus, our findings suggest that provisioning quantity and quality during the early life, affects variation in behavioural phenotypes, which occurs mainly at the within‐individual level. [ABSTRACT FROM AUTHOR]

Wetland habitats experienced a dramatic reduction and fragmentation of biodiversity, because of human activities such as urbanization and agriculture. Now birds, as indicator of this biodiversity, have to breed, winter or stopover in wetlands embedded in a complex and highly altered human matrix. They may concentrate their activities in the wet remnant (wet reedbed) or suboptimal habitats (dry reedbed) and surroundings such as agricultural fields (maize). In a wide wetland area situated south-west of France in a main migration route, we tested if the abundance of passerine species differs among habitats according to their specialization and ecology (wet reedbed vs dry habitats; aquatics vs generalists; migrant vs local), We attempt to identify the underlying mechanisms of observed variation, looking at: arthropod availability in each habitat, bird diet of five insectivorous species and refuelling capacity of birds. Maize crops hosted more invertebrates and biomass than reedbeds for Coleoptera, Diptera, Araneida and Cicadellidae. This may explain why crops were used by aquatic passerines (Bluethroat, Sedge warblers, Reed warblers), migrant or local generalists (Robin, Blue tit, Great tit, Willow Warblers and Nightingale). Bluethroat's diet was more focused on Formicidae and used the both habitats. In spite of the available food in maize, specialist birds preferred reedbed: Cetti warbler feeding in mainly Araneida and Cicadellidae; Sedge warbler Aphid and Coleoptera. Dry reedbed were better used by Grasshopper Warblers foraging Formicidae. Sedge and Reed warblers were more abundant in wet reedbed. We also noted for this last species youngs refuelling in maize crop. Therefore, the strategy to use maize crop may be different if resident or migrant. Generalist resident may disperse searching for food or transit area in continuity of vegetation; migrant need refuelling, particularly the aquatic trans-saharans more specialist on reedbed than the others. Finally, maize crop provided food resources and suitable shelter for a large group of species. It may be a supplement habitat of the wet and dry reedbeds, but not a substitute. Our study reaffirms to conserve and extend wet reedbed habitats threatened by clogging bush encroachment and drying. [ABSTRACT FROM AUTHOR]

Anthropogenic pressures such as over-urbanization, intensive agriculture/forestry practices, and the development of energy farms alter natural landscapes. Intensive urban development poses the greatest threat to natural ecosystems. Habitat degradation, fragmentation, and loss are among the key factors behind the current rise of biodiversity loss. In this study, we hypothesized that urbanization advances the adaptation of forest bird populations to relatively new urban ecosystems. The study was conducted in Kaunas, Lithuania, located in Eastern Europe. Genetic samples were collected in the city, representing urban landscapes, and its surrounding forests. In total, 160 nest boxes were erected, of which 80 were placed in the urban areas and 80 in the forests. Using a set of microsatellite markers, we investigated the genetic differentiation, genetic diversity, gene flow, and population structure of two common forest bird species of the Paridae family, the great tit (Parus major) and blue tit (Cyanistes caeruleus), in forests and urbanized areas. We observed low but significant differences between urban and forest great tit and blue tit populations, proving relatively high population genetic diversity. We determined that cities' spatial structure and fragmented natural habitats can influence the formation of small and isolated bird populations (subpopulations). Urban blue tits had higher genetic differentiation and a higher tendency to form subpopulations. In conclusion, forest birds can inhabit urbanized landscapes but both great tits and blue tits respond differently to urbanization-related changes. [ABSTRACT FROM AUTHOR]

Urban areas, i.e. dense housing and reduced green spaces, can significantly impact avian health, through altering land use and increasing biotic and abiotic stress. This study assessed the association of urbanization on haemosporidian infections, vectors, immune response, and body condition in Parus major nestlings, across four classes of urbanization along an urban-to-rural gradient in Vienna, Austria. Contrary to our expectations, vector abundance remained consistent across the gradient, while an increase in leukocyte count is positively associated with total parasite intensity. We found that nestlings in more urbanized areas exhibited higher parasite intensity and altered immune response, as evidenced by variations in the heterophil to lymphocyte ratio and leukocyte counts. Culicidae female vectors were associated with nestlings' total parasites, scaled mass index, and industrial units. Nestlings in highly developed areas had higher infection rates than those in forests, suggesting increased exposure to infections. However, there was no clear relationship between total female vectors and total parasites. The level of urbanization negatively affected nestling body condition, with a decrease in fat deposits from forested to highly urbanized areas. Our findings highlight the complex interplay between urbanization, vector-borne parasite transmission, and host immune response, emphasizing the need for comprehensive urban planning to improve wildlife health and guarantee ecosystem functioning. Understanding how urbanization affects bird immunity and parasite infections is critical for adapting urban landscapes for wildlife health and ecosystem integrity. [ABSTRACT FROM AUTHOR]

Performance in tests of various cognitive abilities has often been compared, both within and between species. In intraspecific comparisons, habitat effects on cognition has been a popular topic, frequently with an underlying assumption that urban animals should perform better than their rural conspecifics. In this study, we tested problem-solving ability in great tits Parus major, in a string-pulling and a plug-opening test. Our aim was to compare performance between urban and rural great tits, and to compare their performance with previously published problem solving studies. Our great tits perfomed better in string-pulling than their conspecifics in previous studies (solving success: 54%), and better than their close relative, the mountain chickadee Poecile gambeli, in the plug-opening test (solving success: 70%). Solving latency became shorter over four repeated sessions, indicating learning abilities, and showed among-individual correlation between the two tests. However, the solving ability did not differ between habitat types in either test. Somewhat unexpectedly, we found marked differences between study years even though we tried to keep conditions identical. These were probably due to small changes to the experimental protocol between years, for example the unavoidable changes of observers and changes in the size and material of test devices. This has an important implication: if small changes in an otherwise identical set-up can have strong effects, meaningful comparisons of cognitive performance between different labs must be extremely hard. In a wider perspective this highlights the replicability problem often present in animal behaviour studies. [ABSTRACT FROM AUTHOR]

Phenological adjustment is the first line of adaptive response of vertebrates when seasonality is disrupted by climate change. The prevailing response is to reproduce earlier in warmer springs, but habitat changes, such as forest degradation, are expected to affect phenological plasticity, for example, due to loss of reliability of environmental cues used by organisms to time reproduction.Relying on a two‐decade, country‐level capture‐based monitoring of common songbirds' reproduction, we investigated how habitat anthropization, here characterized by the rural–urban and forest–farmland gradients, affected the average phenology and plasticity to local temperature in two common species, the great tit Parus major and the blue tit Cyanistes caeruleus.We built a hierarchical model that simultaneously estimated fledging phenology and its response to spring temperatures based on the changes in the proportion of juveniles captured over the breeding season.Both species fledge earlier in warmer sites (blue tit: 2.94 days/°C, great tit: 3.83 days/°C), in warmer springs (blue tit: 2.49 days/°C, great tit: 2.75 days/°C) and in most urbanized habitats (4 days for blue tit and 2 days for great tit). The slope of the reaction norm of fledging phenology to spring temperature varied across sites in both species, but this variation was explained by habitat anthropization only in the deciduous forest specialist, the blue tit. In this species, the responses to spring temperature were shallower in agricultural landscapes and slightly steeper in more urban areas. Habitat anthropization did not explain variation in the slope of the reaction norm in the habitat‐generalist species (great tit), for which mean fledgling phenology and plasticity were correlated (i.e., steeper response in later sites).The effects of habitat change on phenological reaction norms provide another way through which combined environmental degradations may threaten populations' persistence, to an extent depending on species and on the changes in their prey phenology and abundance. [ABSTRACT FROM AUTHOR]

A major aim of evolutionary biology is to understand why patterns of genomic diversity vary within taxa and space. Large‐scale genomic studies of widespread species are useful for studying how environment and demography shape patterns of genomic divergence. Here, we describe one of the most geographically comprehensive surveys of genomic variation in a wild vertebrate to date; the great tit (Parus major) HapMap project. We screened ca 500,000 SNP markers across 647 individuals from 29 populations, spanning ~30 degrees of latitude and 40 degrees of longitude – almost the entire geographical range of the European subspecies. Genome‐wide variation was consistent with a recent colonisation across Europe from a South‐East European refugium, with bottlenecks and reduced genetic diversity in island populations. Differentiation across the genome was highly heterogeneous, with clear 'islands of differentiation', even among populations with very low levels of genome‐wide differentiation. Low local recombination rates were a strong predictor of high local genomic differentiation (FST), especially in island and peripheral mainland populations, suggesting that the interplay between genetic drift and recombination causes highly heterogeneous differentiation landscapes. We also detected genomic outlier regions that were confined to one or more peripheral great tit populations, probably as a result of recent directional selection at the species' range edges. Haplotype‐based measures of selection were related to recombination rate, albeit less strongly, and highlighted population‐specific sweeps that likely resulted from positive selection. Our study highlights how comprehensive screens of genomic variation in wild organisms can provide unique insights into spatio‐temporal evolutionary dynamics. [ABSTRACT FROM AUTHOR]

This article, titled "Studying Interspecific Synchrony in Bird Survival Using Constant Effort Sites Mist‐Netting Scheme," explores the synchrony in annual adult survival among songbird species across France. The researchers used a constant effort sites mist‐netting scheme to capture and study the birds without causing harm. They found that the survival rates were largely synchronous among species, despite their different ecological niches, life histories, and migratory strategies. However, the causes of this synchrony remain unclear, and further monitoring is needed to investigate the factors driving interspecific survival at a national scale. [Extracted from the article]

Beyond preferences for particular species of tree, bark-foraging birds are associated with various tree characteristics such as decay stage, trunk diameter, or bark roughness. Our objectives were to study the winter foraging ecology of different bark-foraging bird species in the highly diverse floodplain forests of Donau-Auen National Park (Austria) by examining the importance of tree species and characteristics. We used 'first-foraging' observations on the great spotted woodpecker (Dendrocopos major), middle spotted woodpecker (Leiopicus medius), Eurasian nuthatch (Sitta europaea), treecreepers (Certhia spp.), great tit (Parus major), Eurasian blue tit (Cyanistes caeruleus), and marsh tit (Poecile palustris). We examined bird-tree relationships with a bird-plant network approach, where we compared traits of trees and their preferences among avian species. The five most important tree species relative to distance-weighted fragmentation were European white elm (Ulmus laevis), pedunculate oak (Quercus robur), common ash (Fraxinus excelsior), and white and black poplar (Populus alba, P. nigra). Avian taxa differed only in the use of tree condition, where woodpeckers used decayed and dead trees more than tits. Most species preferred trees of larger trunk diameter with rougher bark. We suspect that changes in these highly diverse floodplain forest stands will eventually lead to changes in bark-foraging bird assemblages. For the protection of such highly diverse floodplain forests, conservation-based water management practices will be crucial to maintaining a sufficient groundwater table. Our findings also suggest that forest management practices should focus on more diverse commercial forest stands with a critical amount of secondary tree species, a variety of size classes, varying tree conditions, and species with different bark roughness classes. [ABSTRACT FROM AUTHOR]

Simple Summary: For decades, numerous hypotheses have been suggested to explain why nest characteristics should be associated with reproductive success. However, quantitative intraspecific studies of associations between variations in nest architecture and breeding success remain rare, and they are most often conducted on model species of which nests can be easily monitored with artificial nest-boxes. Here, we review the published literature dealing with the reproductive consequences of nest design in the best-studied secondary-cavity-nesting bird species. We show that research protocols and findings are often poorly replicated across repeat studies. We discuss why many field studies report weak associations between nest architecture characteristics and breeding success and propose suggestions for future research directions. More than 40 hypotheses predict associations between features of nest architecture and at least one measure of reproductive success. However, quantitative studies of reproductive consequences of nest characteristics remain scarce. In addition, most studies were conducted on model species of which nests can be easily monitored with artificial nest-boxes. Here, we review the replicability of research protocols and findings in model species, with many repeat studies focusing mainly on nest-size components, animal-derived nest material, or fresh greenery in model species of secondary hole-nesting birds: Blue Tits (Cyanistes caeruleus), Great Tits (Parus major), Tree Swallows (Tachycineta bicolor), and Starlings (Sturnus spp.). The studies looked for correlations between nest traits and aspects of breeding performance that can be easily quantified in the field, such as clutch size, brood size at hatching or fledging, the percentage of eggs that hatch or fledge, or nestling characteristics assumed to reflect qualities associated with survival probabilities (e.g., morphometry, body condition, blood profiles). We discuss the consequences of poor replicability of research methodologies and provide explanations for why many of these studies reported poor associations between nest design and breeding success at different spatiotemporal scales. We also make suggestions for future research. [ABSTRACT FROM AUTHOR]

Animals use colours, morphological structures and behaviour to advertise their dominance status and ability to obtain resources (Resource Holding Potential, RHP) in agonistic contexts with conspecifics. Dominance relationships are also known between species, although the interactions and the information used to assess the other species' RHP remain obscure and empirical evidence of interspecific recognition of status is hard to obtain. Using behavioural inference is particularly important when a species needs to assess the potential loss of fitness in terms of reproduction or survival (e.g., risk of damage or predation) that could be inflicted by another species acting as a predator, parasite or competitor. Our study shows for the first time the existence of interspecific recognition of status signals: Blue tits Cyanistes caeruleus (subordinate species) perceive Great tits Parus major (dominant species) as threats as hole‐nesting competitors, and respond differently based on the size of the great tit's black tie stripe. Blue tits seemed to recognize the meaning of great tits' black ties because they were bolder when defending their nests against small‐tie (less dominant) great tits than when repelling attacks by large‐tie (more dominant) great tit males. Our results stress that behavioural inference can potentially be used to assess the meaning of status signals that presumably evolved in an intraspecific signalling context. [ABSTRACT FROM AUTHOR]

The harlequin ladybird (Harmonia axyridis) shows a high level of colour polymorphism. Particular forms differ in their colour combination, pattern and abundance.Two species of wild‐caught passerines native to Central Europe were offered various forms of ladybirds, differing in their colour pattern and abundance in nature. We predicted that those forms that are more abundant in the wild are better protected, as they are more familiar to predators.Forms novemdecimsignata and spectabilis, which represent 97% of individuals in the wild population, significantly differ in their visual appearance (mostly orange vs. mostly black). The form axyridis is very rare in the wild, and suturalis and aninkae do not occur in the wild and were derived from laboratory breedingsAs predators, we used great tits (Parus major), which are very aversive towards ladybirds, and tree sparrows (Passer montanus), which are quite willing to attack and even eat ladybirds.We compared bird responses to particular ladybird colour forms and included a brown‐painted control to test the effect of conspicuous colours.We showed that both species of birds attacked all conspicuous forms of the ladybird equally and usually very rarely. The brown‐painted novemdecimsignata form was attacked more frequently compared with the conspicuous forms, showing that the visual appearance prevents birds from attacking any conspicuous colour combination. Sparrows tended to eat the attacked ladybirds of forms novemdecimsignata, spectabilis and brown painted. The rare axyridis form and laboratory forms were very well protected from the attack, very likely due to neophobia.We may conclude that despite the outstanding polymorphism of H. axyridis, its protection against avian predators is very effective as long as the red‐and‐black pattern is preserved. [ABSTRACT FROM AUTHOR]

Located at the crossroads of two continents and at the southeastern edge of the Mediterranean Basin, Anatolia was one of the most important Pleistocene glacial refugia in the Western Palaearctic. As part of the Irano-Anatolian, Caucasus and Mediterranean Basin biodiversity hotspots, this region is also home to a rich avian community including nearly 400 breeding species. Nevertheless, research addressing the genetic structure and diversity of local bird populations is limited, and information on glacial refugia in this region is still scant, especially when compared to other large Mediterranean peninsulas, namely the Balkan, Italian and Iberian ones. In this study, we contribute to filling this gap by addressing the biogeographic pattern of four common resident songbirds—the Eurasian blue tit (Cyanistes caeruleus), the great tit (Parus major), the Eurasian chaffinch (Fringilla coelebs) and the Eurasian blackbird (Turdus merula)—and one endemic species—the Krüper's nuthatch (Sitta krueperi)—by amplifying two mitochondrial DNA genes in individuals from Anatolia (n = 329) and comparing their sequences to those of conspecifics from the rest of their distribution range across the western Palaearctic (n = 357) deposited in public databases. The overall genetic structure of these species is consistent with a scenario of isolation for multiple populations in different refugia across Anatolia and subsequent secondary contact in the wake of ice retreat, which makes this region a hotspot of genetic diversity for both widespread and endemic avian species. [ABSTRACT FROM AUTHOR]

Experiments since the classic studies of Niko Tinbergen have provided evidence that animals use visual landmarks to navigate. We tested whether birds use visual landmarks to relocate their nest sites by presenting two species of cavity nesting birds with a dyad of nest boxes with different white markings around the entrance, a circle or a triangle. When the two boxes were erected in close proximity on the same tree, pied flycatchers Ficedula hypoleuca and blue tits Cyanistes caeruleus confused the entrance of their nest both when the boxes had different external markings and when they were unmarked. Most females added nest material to both boxes of a dyad and one third of the flycatchers laid eggs in both boxes although a female can only incubate the eggs in one nest at a time. Thus, the birds did not use external markings around cavity entrances for orientation. We also tried to replicate a previous study purporting to show that migratory birds use social learning of the external appearance of nests from other species. However, pied flycatchers did not choose boxes with the same painted markings as those applied to nests of resident great tits Parus major which were judged to be high quality "demonstrators" from their large clutch sizes. We argue that conclusions from previous studies on social learning based on external markings as landmarks on nest cavities in birds need to be reconsidered. Significance: Animals may try to hide their nest site on the landscape to avoid the attention of predators and competitors. However, this may make it difficult in the beginning of the breeding season for the parents to relocate the nest site quickly, particularly in a habitat with a complex three-dimensional structure of bushes and trees. To test whether birds might use conspicuous markings around the entrance of their nest as landmarks, we presented prospecting pied flycatchers Ficedula hypoleuca and blue tits Cyanistes caeruleus with a dyad of nest boxes painted with a white circle or a white triangle affixed to different trees or the same tree. However, we found no evidence that the birds used the external markings to identify the entrance to their nest site, or that such markings on nest cavities were learned from resident great tits Parus major. [ABSTRACT FROM AUTHOR]

As urbanization expands, so does the presence of anthropogenic materials within bird's nests. However, our understanding of this phenomenon remains limited, particularly in terrestrial birds. This study describes and compares the use of anthropogenic materials in great tit (Parus major) and blue tit (Cyanistes caeruleus) nests in relation to the intensity of anthropogenic activities, distance to contamination sources and reproductive metrics, in nest boxes in a suburban wood in Coimbra, Portugal, during the breeding seasons of 2020 and 2021. Nests were collected after fledging and sorted to remove anthropogenic materials. From a total of 9.71% anthropogenic materials in great tit nests we observed an abundance of uncoloured tangles of mixed fibres, representing 78% of the total weight of the anthropogenic materials in great tit nests in 2021. The chemical composition of these mixtures was determined by spectroscopy analysis, using Fourier transform infrared spectroscopy (FTIR), and 56% of the nests (16/25) contained fibres from synthetic origin. The percentage of anthropogenic materials was higher in great tit than in blue tit nests and increased in 2021, comparatively to 2020. The proximity to potential contamination sources influenced positively the percentage of anthropogenic materials in nests, as those closer to areas with more intense anthropogenic activities (the bar/tennis court and the wastewater treatment plant) had a higher percentage of these materials. No effects on productivity were detected. Our results suggest that the use of these materials is probably related to the intensity of anthropogenic activities. [ABSTRACT FROM AUTHOR]

The temperature experienced by avian embryos during development has important impacts on their growth and post‐hatching phenotypes. Ambient temperature can directly affect avian nest temperature and indirectly affect it through its impact on parental incubation behaviours. Because the nests of uniparental incubators are usually left unattended more frequently than the nests of biparental incubators whose nests can be attended by another bird when one bird leaves the nest, we predict that the effect of ambient temperature on nest temperature and thus on embryonic development (specifically, incubation period length and hatching success) and post‐hatching phenotype (i.e. potential carry‐over effect on nestling body mass and condition) should be greater in uniparental incubators than in biparental incubators. To test this prediction, we studied two congeneric species, the biparental incubating black‐throated tits Aegithalos concinnus and the uniparental incubating silver‐throated tits A.glaucogularis. We found that although the embryos of the two species both developed faster (shorter incubation period length) when ambient temperature was higher, the slope was significantly greater for silver‐throated tits than for black‐throated tits, consistent with our prediction of a greater effect of ambient temperature on embryonic development in silver‐throated tits. However, the result was not due to a greater effect of ambient temperature on nest temperature, because nest temperatures of the two species had positive relationships with ambient temperature in a similar way. Therefore, it implies a greater response of silver‐throated tit embryos to temperature change. In addition, ambient temperature during the incubation stage did not affect either hatching success or nestling body mass and condition in both species. Although our predictions were not fully supported, our findings highlight the different responses of embryonic development to environmental changes between a uniparental incubator and a biparental incubator, and suggest further research to explore the mechanisms. [ABSTRACT FROM AUTHOR]

We present a high-resolution, densely sampled data set of wild bird songs collected over multiple years from a single population of great tits, Parus major , in the U.K. The data set includes over 1 100 000 individual acoustic units from 109 963 richly annotated songs, sung by more than 400 individual birds, and provides unprecedented detail on the vocal behaviour of wild birds. Here, we describe the data collection and processing procedures and provide a summary of the data. We also discuss potential research questions that can be addressed using this data set, including behavioural repeatability and stability, links between vocal performance and reproductive success, the timing of song production, syntactic organization of song production and song learning in the wild. We have made the data set and associated software tools publicly available with the aim that other researchers can benefit from this resource and use it to further our understanding of bird vocal behaviour in the wild. • We present a large data set of songs from a wild population of great tits. • It contains 1.1 M acoustic units from 109 K songs recorded over several years. • It includes extensive metadata and annotations. • The data set and associated software tools are publicly available. [ABSTRACT FROM AUTHOR]

Understanding the potential limits placed on organisms by their ecophysiology is crucial for predicting their responses to varying environmental conditions. A main hypothesis for explaining avian thermoregulatory mechanisms is the aerobic capacity model, which posits a positive correlation between basal (basal metabolic rate [BMR]) and summit (Msum) metabolism. Most evidence for this hypothesis, however, comes from interspecific comparisons, and the ecophysiological underpinnings of avian thermoregulatory capacities hence remain controversial. Indeed, studies have traditionally relied on between‐species comparisons, although, recently, there has been a growing recognition of the importance of intraspecific variation in ecophysiological responses. Therefore, here, we focused on great tits (Parus major), measuring BMR and Msum during winter in two populations from two different climates: maritime‐temperate (Gontrode, Belgium) and continental (Zvenigorod, Russia). We tested for the presence of intraspecific geographical variation in metabolic rates and assessed the predictions following the aerobic capacity model. We found that birds from the maritime‐temperate climate (Gontrode) showed higher BMR, whereas conversely, great tits from Zvenigorod showed higher levels of Msum. Within each population, our data did not fully support the aerobic capacity model's predictions. We argued that the decoupling of BMR and Msum observed may be caused by different selective forces acting on these metabolic rates, with birds from the continental‐climate Zvenigorod population facing the need to conserve energy for surviving long winter nights (by keeping their BMR at low levels) while simultaneously being able to generate more heat (i.e., a high Msum) to withstand cold spells. Research Highlights: Great tits from a continental climate save energy by keeping a low BMR, yet generate heat (high Msum) to endure cold spells.Metabolic rate coupling is likely guided by distinct selective pressures, shaping local climate‐driven adaptations. [ABSTRACT FROM AUTHOR]

Artificial light at night (ALAN) widely affects wildlife by blurring light‐dark differences, including transitions such as sunrise and sunset, thereby affecting regulation of diel rhythms. As a result, activity onsets in many wild diurnal songbirds advance under ALAN. From chronobiological studies, it is known that the direction and strength of the response to light depends on when during the night exposure takes place. However, these experiments are mostly done under continuous light conditions, when animals have free‐running rhythms. It remains unclear whether phase‐dependence also holds in entrained, wild songbirds; i.e., does the effect of ALAN on activity patterns differ between exposure in the morning compared to the evening? This information is essential to assess the effects of mitigation measures by limiting ALAN to selected times of the night. We exposed incubating great tits (Parus major) inside the nest‐box to 4 h of dim light, of which 1 h overlapped with dawn before sunrise or dusk after sunset. We found a small advancing effect of morning‐light on activity onset and of evening‐light on offset compared to dark controls but not vice versa. Breeding success and chick condition were unaffected by the light treatments. However, light‐treated females had lower weights 9–18 days after the end of the treatment compared to the controls, independent of whether ALAN occurred in the morning or the evening, indicating possible costs of ALAN. Despite the weak behavioral response, ALAN might have affected the females' circadian clock or physiology resulting in lower body condition. Research Highlights: Part‐night lighting alters natural shifts in incubation activity patterns. Thus, onset advanced by light in the early morning and offset by light in the early evening compared to dark controls, and led to lower body weights. [ABSTRACT FROM AUTHOR]

Glucocorticoids are known to adjust organismal functions, such as metabolism, in response to environmental conditions. Therefore, these hormones are thought to play a key role in regulating the metabolically demanding aspects of reproduction, especially in variable environments. However, support for the hypothesis that variation in glucocorticoid concentrations predicts reproductive success is decidedly mixed. Two explanations may account for this discrepancy: (i) Glucocorticoids might not act independently but could interact with other physiological traits, jointly influencing reproduction, and (ii) such an association could become apparent primarily in challenging environments when glucocorticoid concentrations increase. To address these two possibilities, we determined natural variation in circulating baseline glucocorticoid concentrations in parental great tits (Parus major) alongside two physiological systems known to be related with an individual's metabolism: oxidative status parameters (i.e., concentrations of pro‐oxidants, dietary, and enzymatic antioxidants) and body condition. These systems interact with glucocorticoids and can also influence reproductive success. We measured these variables in two breeding seasons that differed in environmental conditions. When accounting for the interaction of baseline glucocorticoids with other physiological traits, we found a positive relationship between baseline glucocorticoids and the number of fledglings in adult great tits. The strength of this relationship was more pronounced for those individuals who also had high concentrations of the enzymatic antioxidant glutathione peroxidase. When studied independently, glucocorticoids were not related to fitness proxies, even in the year with more challenging environmental conditions. Together, our study lend to support the hypothesis that glucocorticoids do not influence fitness alone, but in association with other physiological systems. [ABSTRACT FROM AUTHOR]

Most of our knowledge of secondary hole-nesting birds comes from populations breeding in human-provided nestboxes, yet these might differ from natural cavities in a number of parameters, including internal dimensions or microclimate, leading to differences in reproductive ecology. Here, we demonstrate differences in plumage coloration, an important visual signal of individual quality, in Blue Tit (Cyanistes caeruleus) and Great Tit (Parus major) nestlings raised in natural cavities and nestboxes. For this study, we collected feather samples over two breeding seasons and applied reflectance spectrophotometry to calculate color metrics. Carotenoid chroma was higher in nestbox-reared Blue Tits, whereas brightness was higher in nestbox-reared Great Tits (with a similar tendency for Blue Tits). The latter result might be explained by the better nutritional condition of Great Tit nestlings raised in nestboxes. Furthermore, we found no evidence for preference of adults expressing more elaborate plumage towards a specific cavity type in either species. Consequently, we assume that differences in nestling plumage reported here are driven by rearing conditions (nestboxes vs. natural cavities) and not by differences in plumage-based parental quality. Our study adds to the growing body of evidence confirming that anthropogenic environmental modifiers, such as nestboxes, might influence avian physiology and the resulting phenotype. [ABSTRACT FROM AUTHOR]

Nest construction behaviour is widespread among bird species. Causes for the occurrence and great variation in nest characteristics between and within populations are still poorly understood. In this study, we present results concerning nest parameters of Great Tits Parus major and Blue Tits Cyanistes caeruleus over a period of 11 breeding seasons (2012–2022) in two structurally and floristically contrasting study areas in central Poland. The nest depth differed significantly between young (yearlings) and older females (≥ 2 years after hatching) in Blue Tits (but not in Great Tits): younger females tended to build deeper nests. The size and mass of the nest were very variable in both tit species. Blue Tits tended to build deeper and heavier nests than Great Tits. The depth of the nest was positively correlated with nest mass in Great and Blue Tits. In Great Tits, the nest mass (but not nest depth) differed between study sites, with nests being heavier in the forest and the nest depth differed between years; in Blue Tits, there was an interaction between year and study site that affected nest depth. The nest mass (but not depth) from the same nestbox tended to be consistently similar within species in Great Tits and Blue Tits. We argue that the large amount of variation in nest parameters between and within populations of both tit species may be a multi-factorial result of female age, breeding area, breeding season, individual predispositions and the size of the nestbox/natural hole. [ABSTRACT FROM AUTHOR]

Individual variation in the timing of activities is increasingly being reported for a wide variety of species, often measured as the timing of activity onset in the morning. However, so far, the adaptive significance of consistent variation in temporal phenotypes (i.e. the chronotype) remains largely elusive. Potentially, differences in timing of activities may arise as a result of competition among individuals for resources. Less aggressive individuals may try to avoid competition by becoming active earlier during the day when other individuals are still inactive, leading to a positive correlation between chronotype and aggressive personality type (i.e. a behavioural syndrome). To investigate this, we assessed the chronotype of female great tits, Parus major , by measuring emergence time from the nestbox in the morning and experimentally tested their levels of same-sex aggression through simulated territorial intrusion tests. Contradicting our initial hypothesis, consistently more aggressive females became active earlier during the day compared to less aggressive females, which could be caused by shared underlying mechanisms, like pleiotropic effects of sex hormones or gene pleiotropy, which potentially impose constraints on the independent evolution of both traits. Surprisingly, on the within-individual level we found an opposing correlation between emergence time and aggression. Our findings highlight the need for further investigations into the interplay between chronotype and aggression that take the underlying mechanisms into account in order to understand the adaptive significance of this trait association. • We explored the relationship between chronotype and aggression in female great tits. • Females starting activity earlier in the morning had a more aggressive personality. • This observation suggested the presence of a behavioural syndrome. • Intriguingly, we found an opposite correlation within individuals. • These findings may have implications for the evolutionary potential of both traits. [ABSTRACT FROM AUTHOR]

Simple Summary: In everchanging landscapes with intense land use for agriculture, forestry and settlements, songbirds need to adapt their feeding and breeding behaviour according to changing habitats and food supplies. Blue and Great Tits occur in various habitats from forest to park-like sites and strongly rely on caterpillars to feed their offspring. Using genetic analyses of Blue and Great Tit droppings, we compared the diet composition of nestlings among forest, urban parks, and meadows with scattered fruit trees (traditional orchards). Additionally, we compared the food availability in the trees of each habitat to the respective nestling diets. Both bird species showed a diverse diet dominated by butterflies in all habitats. Moth components in the diet were most similar between forest and orchard sites, while components of other insect-like prey were most similar between orchard and urban sites. Both bird species especially selected three major moth families at all sites and alongside two families of sawflies in the orchard and forest sites. Our results on nestling diet and prey preferences provide further insights in the feeding behaviours of Blue and Great Tits among changing anthropogenic landscapes. Moreover, our genetic approach using bird droppings provides a baseline to support insect monitoring. Increasing landscape transformations and urbanisation affect insectivorous bird populations in various ways such as food availability, breeding phenology, or reproductive success. Especially during the breeding season, many passerine birds rely on the availability of caterpillars as the main prey for their nestlings. Previous studies suggested that similar diet preferences of sympatric species may result in interspecific competition, as demonstrated for Blue and Great Tits in forest habitats. However, nestling diet and prey preferences in other habitats are not fully understood. Prey availability, especially caterpillars, is lower in cities than in forests, thus influencing prey choice and interspecific competition. Here we used faecal DNA metabarcoding to investigate if nestling diet composition of the two sympatric species Blue Cyanistes caeruleus and Great Tits Parus major varied among species and different habitats (forest, traditional orchards, and urban parks). Furthermore, we examined food availability by DNA barcoding of the arboreal arthropod communities among habitats and compared them to the nestling diet to infer parental prey selectivity. The study was carried out in central Germany from 2018 to 2019. Blue and Great Tits showed a diverse diet which was dominated by Lepidoptera in all habitats. Lepidopteran diet components were most similar between forest and orchard sites, as were the components with other arthropods between orchard and urban sites. Both tit species showed selectivity for the lepidopteran families Geometridae and Tortricidae in all habitats, and for Noctuidae (Lepidoptera), Tenthredinidae and Braconidae (Hymenoptera) in forest and orchard sites. As the tits showed preferences for mainly families of Lepidoptera, and Hymenoptera, our approach provides a baseline to support monitoring of these groups. [ABSTRACT FROM AUTHOR]

Adverse, postnatal conditions experienced during development are known to induce lingering effects on morphology, behaviour, reproduction and survival. Despite the importance of early developmental stress for shaping the adult phenotype, it is largely unknown which molecular mechanisms allow for the induction and maintenance of such phenotypic effects once the early environmental conditions are released. Here we aimed to investigate whether lasting early developmental phenotypic changes are associated with post‐developmental DNA methylation changes. We used a cross‐foster and brood size experiment in great tit (Parus major) nestlings, which induced post‐fledging effects on biometric measures and exploratory behaviour, a validated personality trait. We investigated whether these post‐fledging effects are associated with DNA methylation levels of CpG sites in erythrocyte DNA. Individuals raised in enlarged broods caught up on their developmental delay after reaching independence and became more explorative as days since fledging passed, while the exploratory scores of individuals that were raised in reduced broods remained stable. Although we previously found that brood enlargement hardly affected the pre‐fledging methylation levels, we found 420 CpG sites that were differentially methylated between fledged individuals that were raised in small versus large sized broods. A considerable number of the affected CpG sites were located in or near genes involved in metabolism, growth, behaviour and cognition. Since the biological functions of these genes line up with the observed post‐fledging phenotypic effects of brood size, our results suggest that DNA methylation provides organisms the opportunity to modulate their condition once the environmental conditions allow it. In conclusion, this study shows that nutritional stress imposed by enlarged brood size during early development associates with variation in DNA methylation later in life. We propose that treatment‐associated DNA methylation differences may arise in relation to pre‐ or post‐fledging phenotypic changes, rather than that they are directly induced by the environment during early development. [ABSTRACT FROM AUTHOR]

Population density is a fundamental ecological feature influencing the opportunity for social encounters between individuals. Hence, density can impact various population processes such as social transmission. While the density dependence of disease spread has been studied extensively, we know little about how variation in density influences information transmission. If high densities lead to more social connections, information may spread more rapidly. Here, we experimentally manipulated local population density in great tits, Parus major , and investigated the effects on individuals' acquisition of information on novel food patches. We manipulated density by assigning individuals to either a high- or low-density treatment using automated bird feeders in the wild. We first show how our approach successfully led to changes in local population density. Next, we examine how the manipulation changed the local and individual social environment. At the local level, high-density locations resulted on average in denser and more clustered social networks compared to low-density locations. At the individual level, birds assigned to the high-density treatment had on average more social connections and more central network positions than birds in the low-density treatment. However, despite the effect on network structure, we found no evidence that the density manipulation influenced an individuals' likelihood, or speed, of locating novel food patches. Birds in the low-density treatment still spent a large proportion of time foraging at the high-density location. Thus, the manipulation did not lead to a strict segregation between birds of the different treatments, which may be one explanation for the absence of an effect on patch discovery. • We experimentally manipulated population density in wild great tits. • We examined effects of the manipulation on the discovery of food patches. • Higher densities led to denser and more clustered social networks. • Birds in the high-density treatment had more social connections. • We found no evidence for effects on the likelihood and speed of patch discovery. [ABSTRACT FROM AUTHOR]

Abstract Behavioural traits are under both genetic and environmental influence during early life stages. Early environmental conditions related to the amount and type of food have been found to alter behaviour in many organisms. However, how early life diet affects the variation in and the correlation between behavioural traits is largely unknown. Using a multivariate approach, we investigated how variation in parental prey selection is related to three repeatable nestling personality traits, and explored the within and between‐individual covariation between these behaviours in a wild passerine, the great tit (Parus major). Our results confirm that breath rate, docility and handling aggression (HA) in great tit nestlings are repeatable traits. Contrary to our expectation, the three nestling personality traits did not form a behavioural ‘syndrome’ on the phenotypic level in the study population, but we found two of three expected phenotypic correlations, mostly at the within‐individual level. Moreover, we found that breath rate significantly decreased with a higher number of spiders in the diet, and docility and handling aggression were significantly and inversely related to higher numbers of noctuids and tortricids in the diets of individuals within broods. Thus, our findings suggest that provisioning quantity and quality during the early life, affects variation in behavioural phenotypes, which occurs mainly at the within‐individual level.

Increasing landscape transformations and urbanisation affect insectivorous bird populations in various ways such as food availability, breeding phenology, or reproductive success. Especially during the breeding season, many passerine birds rely on the availability of caterpillars as the main prey for their nestlings. Previous studies suggested that similar diet preferences of sympatric species may result in interspecific competition, as demonstrated for Blue and Great Tits in forest habitats. However, nestling diet and prey preferences in other habitats are not fully understood. Prey availability, especially caterpillars, is lower in cities than in forests, thus influencing prey choice and interspecific competition. Here we used faecal DNA metabarcoding to investigate if nestling diet composition of the two sympatric species Blue Cyanistes caeruleus and Great Tits Parus major varied among species and different habitats (forest, traditional orchards, and urban parks). Furthermore, we examined food availability by DNA barcoding of the arboreal arthropod communities among habitats and compared them to the nestling diet to infer parental prey selectivity. The study was carried out in central Germany from 2018 to 2019. Blue and Great Tits showed a diverse diet which was dominated by Lepidoptera in all habitats. Lepidopteran diet components were most similar between forest and orchard sites, as were the components with other arthropods between orchard and urban sites. Both tit species showed selectivity for the lepidopteran families Geometridae and Tortricidae in all habitats, and for Noctuidae (Lepidoptera), Tenthredinidae and Braconidae (Hymenoptera) in forest and orchard sites. As the tits showed preferences for mainly families of Lepidoptera, and Hymenoptera, our approach provides a baseline to support monitoring of these groups.

New research suggests that free-living blue and great tits remember foraging, including food type, location, and time since eating, even when event details were not known to be relevant for a subsequent assessment of memory, implicating the use of episodic memory in natural behavior. [ABSTRACT FROM AUTHOR]

Short-term adaptive evolution represents one of the primary mechanisms allowing species to persist in the face of global change. Predicting the adaptive response at the species level requires reliable estimates of the evolutionary potential of traits involved in adaptive responses, as well as understanding how evolutionary potential varies across a species' range. Theory suggests that spatial variation in the fitness landscape due to environmental variation will directly impact the evolutionary potential of traits. However, empirical evidence on the link between environmental variation and evolutionary potential across a species range in the wild is lacking. In this study, we estimate multivariate evolutionary potential (via the genetic variance–covariance matrix, or G-matrix) for six morphological and life history traits in 10 wild populations of great tits (Parus major) distributed across Europe. The G-matrix significantly varies in size, shape, and orientation across populations for both types of traits. For life history traits, the differences in G-matrix are larger when populations are more distant in their climatic niche. This suggests that local climates contribute to shaping the evolutionary potential of phenotypic traits that are strongly related to fitness. However, we found no difference in the overall evolutionary potential (i.e. G-matrix size) between populations closer to the core or the edge of the distribution area. This large-scale comparison of G-matrices across wild populations emphasizes that integrating variation in multivariate evolutionary potential is important to understand and predict species' adaptive responses to new selective pressures. [ABSTRACT FROM AUTHOR]

The recognition that climate change is occurring at an unprecedented rate means that there is increased urgency in understanding how organisms can adapt to a changing environment. Wild great tit (Parus major) populations represent an attractive ecological model system to understand the genomics of climate adaptation. They are widely distributed across Eurasia and they have been documented to respond to climate change. We performed a Bayesian genome-environment analysis, by combining local climate data with single nucleotide polymorphisms genotype data from 20 European populations (broadly spanning the species' continental range). We found 36 genes putatively linked to adaptation to climate. Following an enrichment analysis of biological process Gene Ontology (GO) terms, we identified over-represented terms and pathways among the candidate genes. Because many different genes and GO terms are associated with climate variables, it seems likely that climate adaptation is polygenic and genetically complex. Our findings also suggest that geographical climate adaptation has been occurring since great tits left their Southern European refugia at the end of the last ice age. Finally, we show that substantial climate-associated genetic variation remains, which will be essential for adaptation to future changes. [ABSTRACT FROM AUTHOR]

During early ontogeny, microbiome affects development of the gastrointestinal tract, immunity, and survival in vertebrates. Bird eggs are thought to be (1) initially sterile (sterile egg hypothesis) and (2) colonized after oviposition through horizontal trans-shell migration , or (3) initially seeded with bacteria by vertical transfer from mother oviduct. To date, however, little empirical data illuminate the contribution of these mechanisms to gut microbiota formation in avian embryos. We investigated microbiome of the egg content (day 0; E0-egg), embryonic gut at day 13 (E13) and female faeces in a free-living passerine, the great tit (Parus major), using a methodologically advanced procedure combining 16S rRNA gene sequencing and microbe-specific qPCR assays. Our metabarcoding revealed that the avian egg is (nearly) sterile, but acquires a slightly richer microbiome during the embryonic development. Of the three potentially pathogenic bacteria targeted by qPCR, only Dietzia was found in E0-egg (yet also in negative controls), E13 gut and female samples, which might indicate possible vertical transfer. Unlike in poultry, we have shown that major bacterial colonization of the gut in passerines does not occur before hatching. We emphasize that protocols that carefully check for environmental contamination are critical in studies with low-bacterial biomass samples. [ABSTRACT FROM AUTHOR]

Foraging decisions under risk of predation are crucial for survival as predation risk can contribute to a reduction of food intake over time leading to a trade-off between starvation and predation. Environmental variation can provoke changes in food accessibility or predation risk that will in turn affect foraging decisions. Specifically, less predictable or harsher environments, such as those found at high elevation, should lead to more risk-prone foraging in order to prevent risk of starvation, but empirical confirmation of this hypothesis is lacking. In the current study, we used video playbacks combined with an automatic feeder to measure continuous foraging choices between control and predator videos by wild great tits originating from high and low elevations and tested under controlled conditions. Great tits discriminated between two conditions representing differences in predation risk and visited the feeder less frequently when a predator was shown. Moreover, we found that birds from low elevation populations were more risk-averse and visited the feeder significantly less when a predator video playback was broadcasted compared with high elevation individuals. This elevation-related contrast was also dependent on the season, body mass, and fat reserves of individuals, and was more marked in females. Furthermore, adults visited the feeder less in the presence of a predator compared with yearlings. These results are consistent with predictions from life-history theory and starvation–predation trade-off hypotheses and could have implications for individual movements and population dynamics in changing environments. [ABSTRACT FROM AUTHOR]

Byzantine kratēmata, widely known as the terrirem, as part of other, broader musical works, date approximately back to the eleventh–twelfth century. A small group of four kratēmata are named after birds (Aēdhon – Luscinia megarhynchos, Potamis – Acrocephalus, Anyfantis and Papadopoula – Parus major). It is reasonable to assume that the singing of the respective birds inspired composers to set these kratēmata to music. Studying the related compositions, as they have been documented in the written tradition of the Byzantine and the post-Byzantine manuscripts until their transcription from the pre-1814 old stenographic method notation, we report certain observations that reinforce the initial hypothesis, as well as some parallel remarks about the phenomenon of creation, establishment, and spreading of this form. [ABSTRACT FROM AUTHOR]

Many species mob predators to drive them away. Mobbing carries personal risk, but the risk of injury or death declines and the likelihood of repelling the predator increases in larger groups. The capacity to evaluate the number of mobbers before joining a mobbing group may be highly beneficial for individuals when deciding to join. Although recent studies have found that birds can use individual vocal discrimination to assess the number of conspecifics involved in initiating mobbing events, it is little known whether birds are able to evaluate the number of heterospecific mobbers. In this study, we investigated whether the number of heterospecifics responding to mobbing calls of Great Tits Parus major was influenced by the number of callers (a mix of Great Tit callers simulated by playbacks and live Great Tits attracted to playbacks, range one to seven callers). The total number of responding heterospecific individuals and species was positively influenced by the total number of callers, with heterospecifics responding more to larger than smaller Great Tit groups. However, these results may be driven by the total number of calls, call overlap and increased noise generated by the additional mobbers, and not the number per se. These findings therefore allow us to assess whether birds are more inclined to join a mobbing group when it consists of more heterospecific callers, but we cannot tell whether birds use individual vocal discrimination to assess the number of heterospecific callers. [ABSTRACT FROM AUTHOR]

After an overview of the discussion about the existence of intra- and interspecific competition that illustrates the contradictory opinions I conclude that long-term field experiments are needed for firm conclusions. I discuss in some detail the role of two factors that limit population size of secondary cavity nesting birds e.g. territorial behavior and adequate cavities. This is followed by an overview of experimental long-term field studies in Belgium showing that intra- and interspecific competition in a great tit-blue tit system exists. By using nestbox configurations with high densities of nestboxes that differ in the diameter of their entrance hole in replicate study plots it is possible to manipulate the breeding densities of great tit Parus major and blue tit Cyanistes caeruleus independently, thereby varying the intensity of intra- and interspecific competition between these two coexisting species. When blue tit densities are experimentally increased local recruitment of great tits increases, and adult great tit post-breeding dispersal to other study plots decreases, implying that great tits use blue tit density to evaluate habitat quality and that high blue tit density results in heterospecific attraction. The reverse is not true. An experimental increase in great tit density leading to an increase in interspecific competition in a plot where blue tit density was already high leads to a decrease in blue tit nestling mass (illustrating interspecific competition for food), but to a gradual increase in blue tit body size. Both are primarily caused by an increase in the body size of immigrants (caused by intraspecific competition for protected roosting holes) in contrast to the control plot, where neither is observed. I also summarize behavioral, ecological and possible evolutionary effects of sparrowhawks on blue tits after sparrowhawks settled in an isolated study plot halfway through the study: adult survival substantially decreased for both sexes, but more for females that laid large clutches, leading to selection for females that laid a smaller clutch. This led to a change in the reproduction/survival life-history trade-off. Adult winter weights and nestling weights decreased, and the heaviest fledglings were selected against. Furthermore the frequency of polygyny increased. The long-term experiments also document the role of the use of public information and that species that compete can be attracted to sites in which competitor density is high. [ABSTRACT FROM AUTHOR]

Traditional models of oxidative stress predict accumulation of damage caused by reactive oxygen species (ROS) production as highly correlated with aerobic metabolism, a prediction under increasing scrutiny. Here, we repeat sampled female great tits (Parus major) at two opposite levels of energy use during the period of maximum food provisioning to nestlings, once at rest and once during activity. Our results were in contrast to the above prediction, namely significantly higher levels of oxidative damage during rest opposed to active phase. This discrepancy could not be explained neither using levels of "first line" antioxidant enzymes activity measured from erythrocytes, nor from total nonenzymatic antioxidant capacity measured from plasma, as no differences were found between states. Significantly higher levels of uric acid, a potent antioxidant, were seen in the plasma during the active phase than in rest phase, which may explain the lower levels of oxidative damage despite high levels of physical activity. Our results challenge the hypothesis that oxidative stress is elevated during times with high energy use and call for more profound understanding of potential drivers of the modulation of oxidative stress such as metabolic state of the animal, and thus also the time of sampling in general. [ABSTRACT FROM AUTHOR]