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Life-history theory predicts that whenever expensive activities overlap, there will be a trade-off between the activities. In a field study of Blue Tits Cyanistes caeruleus in Norway, we tested whether parental energy expenditure during reproduction affected timing of moult of primary feathers. Five days after hatching, we manipulated broods to contain either two (n = 10 broods) or 9–12 nestlings (n = 13). In contrast to previous studies, we measured stage of moult at two time points during the nestling period (7 and 14 days after hatching). The onset of moult in the male but not in the female was strongly affected by a reduction in brood size. Stage of moult did not differ between the experimental groups 7 days after hatching, but did after a further week. This difference was also evident when considering only males that had started moulting on day 7. Male moult score was not related to male age (yearling or older), body size (wing length, tarsus length) or hatching time (calendar date) of the brood. However, body condition, expressed as residuals of the regression of body mass on wing length, tended to be greater for parents of both sexes attending small broods than large broods. None of 23 females had initiated moult 7 days after hatching, and only two had done so by day 14. Surprisingly, moult did not seem to affect food provisioning by males relative to females. These results confirm previous studies of passerine birds, namely, that males may start moulting before females and that the moult can quickly be adjusted to the demands of brood-rearing. The novel result in this case was that such demands affected not only the timing of moult onset but also its speed once it had started.

Nest sites of animals are often concealed to keep vulnerable offspring from being detected by predators. Parents may use landmarks near the nest to relocate it quickly. We allowed blue tits (Cyanistes caeruleus) to choose between two nest boxes fixed on the same tree with either none, the same, or different white painted markings. Surprisingly, the female brought material to both boxes and sometimes laid eggs in both. In a second experiment, we let pied flycatchers (Ficedula hypoleuca) and great tits (Parus major) become familiar with a marking on the initial nest box and then let them choose between two new nest boxes erected on different, nearby trees. Neither species preferred the box with the matching mark. In nature, the birds may locate the correct entrance of a cavity using other landmarks near the nest opening, like branches and the height of the cavity opening above the ground.

Among species that use similar resources, an individual may benefit by observing and copying the behavioural decision of a heterospecific. We tested the hypothesis of heterospecific social learning in passerine birds, namely that a migrant species, the Pied Flycatcher Ficedula hypoleuca, uses external markings on the nest cavities of a resident species, the Great Tit Parus major, as cues when choosing a nest site. Others have suggested that prospecting flycatchers assess the clutch size of tit “demonstrators” by entering their nest boxes and, assuming that a large clutch indicates a high-quality individual, will copy the nest appearance of tits with large, but not small clutches. During a 4-year period in Norway, we designed a similar study but did not find that flycatchers based their nest choice on the clutch size of tits. Neither were there any relationships between clutch size of the tit and its laying date, incubation behaviour, or the number of eggs visible through nest material during egg-laying so Pied Flycatchers did not use these indirect cues to assess quality of the tutor. Filming of tit nests showed that prospecting flycatchers did not enter tit nest boxes to assess the content. Indeed, incubating female tits only left their nest boxes for short bouts of unpredictable duration so there was little opportunity for flycatchers to inspect the nest contents unnoticed. Our study calls into question the mechanism of using the content of tit nests as public information for choosing traits of nest sites based on external characteristics. We suggest that similar studies of nest site choice in relation to possible social information transfer be replicated more widely.

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

Interspecific competition is expected when two species share resource needs. For example, secondary cavity‐nesting birds may compete vigorously for suitable nest sites both within and among species. However, little is known of whether monogamous species defend more than one nest site on their territory after breeding has begun, and in particular whether they are aggressive against other species. Defending extra nest sites may be adaptive because they may be used for renesting after a failure or to produce a second brood. We studied interactions between a monogamous, resident bird, the great tit Parus major and a migrant, the pied flycatcher Ficedula hypoleuca, providing nest boxes in woodlands in Norway. Agonistic behaviours may be subtle and easily overlooked so we experimentally placed caged male pied flycatchers near nests of great tits and at a dyad of empty nest boxes erected in the territory 25 m away. We filmed interactions between species at 21 sites in the egg‐laying period of the tit, and at 26 nest sites during incubation. Male great tits showed aggression towards the caged flycatcher both at their own nest box and at the nest boxes erected at a distance. We manipulated the external appearance of the nest boxes with painted designs around the entrances but the intensity of aggression at the empty nest boxes did not depend on whether those boxes matched the nest box with the tit nest and was not correlated with tit clutch size. Neither was the intensity of display activity at each nest box by the flycatchers that settled associated with these variables. The results are discussed in relation to hypotheses for nest site choice involving interspecific social learning and aggression.

Bird nests often consist of stronger materials to maintain nest structure and a softer layer of lining materials to reduce heat loss. We studied whether early learning affected the use of nest materials by cross-fostering between two tit species with similar breeding ecology, the blue tit, Cyanistes caeruleus, and the great tit, Parus major, in a woodland area provided with nestboxes in Norway. In both species, only the female builds the nest. From previous studies, we know that early social learning affects a number of traits in these birds, including song repertoire, mate choice, foraging behaviour and nest site choice. Nests of the two species are similar but blue tits use more feathers than great tits. This was confirmed in the present study; however, female blue tits raised by great tit foster parents also supplied their nest with feathers, and female great tits raised by blue tits used few feathers. The only treatment effect was that fewer feathers were found in nests of cross-fostered females in both species than in nests of controls. This may have been caused by time and energetic constraints during nest building because cross-fostered birds seemed to forage less efficiently than controls. The amount of hair was slightly greater in blue tits than in great tits, but it was not affected by the cross-fostering either. We conclude that no cultural transmission was found in the use of lining materials in the nest of the two species, perhaps because young birds hatch after their parents have stopped constructing the nest.

The integration and synthesis of the data in different areas of science is drastically slowed and hindered by a lack of standards and networking programmes. Long-term studies of individually marked animals are not an exception. These studies are especially important as instrumental for understanding evolutionary and eco-logical processes in the wild. Furthermore, their number and global distribution provides a unique opportunity to assess the generality of patterns and to address broad-scale global issues (e.g. climate change)., To solve data integration issues and enable a new scale of ecological and evolution-ary research based on long-term studies of birds, we have created the SPI-Birds Network and Database (www.spibirds.org)—a large-scale initiative that connects data from, and researchers working on, studies of wild populations of individually recognizable (usually ringed) birds. Within year and a half since the establishment, SPI-Birds has recruited over 120 members, and currently hosts data on almost 1.5 million individual birds collected in 80 populations over 2,000 cumulative years, and counting., SPI-Birds acts as a data hub and a catalogue of studied populations. It prevents data loss, secures easy data finding, use and integration and thus facilitates collab-oration and synthesis. We provide community-derived data and meta-data stand-ards and improve data integrity guided by the principles of Findable, Accessible, Interoperable and Reusable (FAIR), and aligned with the existing metadata lan-guages (e.g. ecological meta-data language)., The encouraging community involvement stems from SPI-Bird's decentralized ap-proach: research groups retain full control over data use and their way of data management, while SPI-Birds creates tailored pipelines to convert each unique data format into a standard format. We outline the lessons learned, so that other communities (e.g. those working on other taxa) can adapt our successful model. Creating community-specific hubs (such as ours, COMADRE for animal demogra-phy, etc.) will aid much-needed large-scale ecological data integration., The SPI-Birds have been supported by an NWO personal grant (grant number 016.Veni.181.054) to A.C., and a Research Council of Norway grant: 223257 (SFF-III) and 267511 (EVOCLIM).

Natal dispersal is common in animals but the fitness cost of moving from the natal area is not well understood. One reason for a fitness cost is that foraging skills and prey preference learned early in life may be less efficient if the individual settles in a new, unfamiliar habitat. In a 4-year study, we found that immigrant parent blue tits, Cyanistes caeruleus, and great tits, Parus major, were inferior food providers compared to local recruits. In blue tits, immigrants provided smaller prey items than local recruits, whereas in great tits, the immigrants provided fewer green larvae, but relatively more brown larvae, to the offspring than local recruits. We also found that immigrant females laid later or smaller clutches than females locally recruited. The results are consistent with the hypothesis that natal dispersal carries costs related to the learning of foraging skills. However, alternative explanations are that the differences were caused by genetic and/or quality differences between the two groups of birds. We discuss various ecological and behavioural traits that may influence, and be influenced by, the mismatch of foraging between natal and breeding habitats. In altricial birds, yearlings will not have previous foraging experience during breeding and, in addition, immigrants will not have spent a long postfledging period in the new local habitat with their parents. If there are foraging-habitat mismatches as a result of dispersal, researchers should include natal origin in models of optimal foraging, time budgets, reproductive success and survival because performance may be directly related to the early learning environment rather than genetic differences.

A major aim of evolutionary biology is to understand why patterns of genomic variation vary among populations and species. Large-scale genomic studies of widespread species are useful for studying how the environment and demographic history shape patterns of genomic divergence, and with the continually decreasing cost of sequencing, such studies are now becoming feasible. Here, we carry out one of the most 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 almost the entire geographic range of the European great tit subspecies. We found that genome-wide variation was consistent with a recent colonisation across Europe from a single refugium in the Balkans and/or Turkey, with bottlenecks and reduced genetic diversity in island populations. Differentiation across the genome was highly heterogeneous, with clear “islands of differentiation” even among populations which are ostensibly panmictic. These islands of differentiation were consistently found in regions of low recombination, suggesting that background selection can rapidly promote population differentiation among even the most recently colonised populations. We also detected genomic outlier regions that were unique to peripheral great tit populations, most likely as a result of recent directional selection at the range edges of this species. These “unique” outlier regions contained candidate genes for morphology, thermal adaptation and colouration, supporting previous research in this species, and providing avenues for future investigation. Our study suggests that comprehensive screens of genomic variation in wild organisms can provide unique insights into evolution. Author summary Studying patterns of genetic variation is a useful way of determining why populations and species differ in nature. Genetic variation is shaped by natural selection, but also by the present and past size of populations, the amount of migration, and by features of the genome, such as variation in recombination rate, of the organism being studied. Teasing apart the effects of these different processes on genomic diversity is difficult, but one way that this can be achieved is by studying genomic variation across the entire range of a species. We performed a continental-scale analysis of genetic variation in the great tit - a widespread songbird that has been the focus of extensive ecological research. We first used genomic data to reconstruct the historical colonisation of great tits across Europe, and showed that during the last ice age, this species was likely restricted to a single region in Eastern Europe, from which they spread across the continent. We then studied how patterns of variation differ along the genome, and show that recombination rate is a key driver of variation among all populations. Importantly, by comparing many populations we were able to identify genes that have been subject to natural selection in specific geographical regions. We found that natural selection appeared to be strongest in populations on the edges of the great tit’s range acting on traits such as morphology, stress response and colouration. Large-scale genetic analyses such as ours are therefore useful approaches for understanding how evolution operates in the wild.

Recent climate change has led to advanced spring phenology in many temperate regions. The phenological response to variation in the local environment, such as the habitat characteristics of the territories birds occupy, is less clear. The aim of this study is to understand how ecological conditions affect breeding time, and its consequences for reproduction, in a white-throated dipper Cinclus cinclus population in a river system in Norway during 34 years (1978–2011). Hatching date advanced almost nine days, indicating a response to higher temperatures and the advanced phenology in the area. Earlier breeding was found in warm springs and at lower altitudes. High population density facilitated earlier breeding close to the coast. Furthermore, when population density was low, breeding was early at territories that were rarely occupied, while in years with high density, breeding was early at territories that were frequently occupied. Also, when population density was low, earlier breeding occurred at territories that on average produced more offspring than other territories, while there was no difference in breeding time in high population years. Selection for early breeding was dependent on spring temperatures and high spring temperatures contributed to higher breeding success during the study period. We found that breeding phenology may have strong effects on fitness in the white-throated dipper, and thus that breeding time is an important ecological factor in a species that feeds mainly on aquatic rather than terrestrial prey.

Gene flow is usually thought to reduce genetic divergence and impede local adaptation by homogenising gene pools between populations. However, evidence for local adaptation and phenotypic differentiation in highly mobile species, experiencing high levels of gene flow, is emerging. Assessing population genetic structure at different spatial scales is thus a crucial step towards understanding mechanisms underlying intraspecific differentiation and diversification. Here, we studied the population genetic structure of a highly mobile species - the great tit Parus major - at different spatial scales. We analysed 884 individuals from 30 sites across Europe including 10 close-by sites (< 50 km), using 22 microsatellite markers. Overall we found a low but significant genetic differentiation among sites (F-ST = 0.008). Genetic differentiation was higher, and genetic diversity lower, in south-western Europe. These regional differences were statistically best explained by winter temperature. Overall, our results suggest that great tits form a single patchy metapopulation across Europe, in which genetic differentiation is independent of geographical distance and gene flow may be regulated by environmental factors via movements related to winter severity. This might have important implications for the evolutionary trajectories of sub-populations, especially in the context of climate change, and calls for future investigations of local differences in costs and benefits of philopatry at large scales. (C) 2016 The Linnean Society of London, The study was funded by the Swiss National Science Foundation (3100A0-102017 to HR, P2BEP3_152103 to KL and PMPDP3_151361/161858 to ML). We thank L. Gustafsson and J. Forsman who kindly allowed us to use their nest boxes. We gratefully thank E. Bezault, L. Cornetti and two anonymous reviewers for valuable advice on genetic analyses and helpful comments on the manuscript. All samples were collected under licenses of national authorities and financially supported by the Academy of Finland grant (to NP and 265859 to TE), the Netherland Organisation for Scientific Research (NWO-VICI 86503003 to JK and NWO-VICI to MV), the Netherlands Genomics Initiative (Horizon grant to KvO), the Hungarian Scientific Research Fund (OTKA 75618 to JT), the Estonian Ministry of Education and Science (IUT 34-8 to RM), the OSU-OREME, the Spanish Ministry of Education and Science (CGL2010-21933-CO-02 to EB), the Portuguese Foundation for Science and Technology (SFRH/BD/13594/2003 to ACN) and the Agence Nationale de la Recherche (ANR-08-JCJC-0041-01 to BD).

The Willow Tit Poecile montanus is highly sedentary and breeding pairs remain in their exclusive areas throughout the year. During the winter, these areas are defended by small, non-kin flocks, formed as the roaming yearlings become sedentary and join adults during late summer and autumn. Once established, stable social hierarchies are maintained in these flocks during the winter. The winter flocks consist normally of the socially dominant adult mated pair and two mated juvenile pairs, one higher-ranked and one lower-ranked. Individually colour-ringed juvenile Willow Tits were followed over years in subalpine forest in Norway from ringing in the autumn till they disappeared. None of the lower ranked birds survived their first winter, whereas only 4 of 71 higher-ranked juvenile pairs disappeared during this time. Half of the 71 pairs survived their first winter, about 25 % survived two winters, 8.5% survived three winters, and 5.6% survived four winters. Survival was similar for males and females. Alpha pairs remained mated and defended their common territory across years. Maximum age as revealed by ringing showed one female became six years old and two males ringed as adults were at least nine years old when last observed. The main factor associated with survival was early flock establishment that led to a high rank position among the juvenile flock members. Body size seemed insignificant. Birds that survived their first winter either succeeded to establish as territory owners or they were forced into the role as floaters and probably perished. Tidsskriftet er åpent for alle (Open Access), det vil si fri og gratis tilgang til alt publisert innhold. Lesere av tidsskriftet kan ta utskrift av de fremførte manuskriptene under samme betingelser som gjelder ved kopiering av fysiske eksemplar. Dette innebærer at masseframstilling av fysiske eksemplar, eller framstilling av eksemplar for kommersielle formål, ikke er tillatt uten etter avtale med forfatteren(e).

Optimal foraging theory suggests that avian parents should prefer the most energetically efficient (largest) prey items when delivering food to offspring at a central place. However, during periods of high demand, selectivity of prey may decline, leading to the delivery of smaller and/or less nutritious items. We compared foraging trade-offs between great tits (Parus major) which had a wider feeding niche than blue tits (Cyanistes caeruleus). We also compared the foraging efficiency of cross-fostered young, which had learned the spatial foraging niche and prey size of the foreign species, to that of control conspecifics. Mean delivery rates did not differ between control and cross-fostered parents of either species but as delivery rates increased, prey size declined for both species and both treatment groups. However, across the range of increasing delivery rates, parents were able to increase the total biomass of prey delivered. Cross-fostering did not alter the proportion of different prey taxa in the diet, but cross-fostered birds shifted the size of the prey taken to that of their foster species. Consistent with their broader feeding niche, great tits, but not blue tits, incorporated more unpalatable items (flies) as delivery rates increased. Although great tits foraged less efficiently in the blue tit niche, paradoxically, blue tits seem to deliver more prey biomass when foraging in the great tit niche.

This research has been accepted and published in the Journal of Avian Biology. © 2017 Wiley

Warmer winters alter the dynamics of a local bird population and reduce immigration rate due to density-dependent feedback., Climate change will affect the population dynamics of many species, yet the consequences for the long-term persistence of populations are poorly understood. A major reason for this is that density-dependent feedback effects caused by fluctuations in population size are considered independent of stochastic variation in the environment. We show that an interplay between winter temperature and population density can influence the persistence of a small passerine population under global warming. Although warmer winters favor an increased mean population size, density-dependent feedback can cause the local population to be less buffered against occasional poor environmental conditions (cold winters). This shows that it is essential to go beyond the population size and explore climate effects on the full dynamics to elaborate targeted management actions.

Raptors deviate from the norm among provisioning birds by having asymmetric parental roles, with the female brooding and feeding offspring, and the male providing food, assisted by the female from the latter part of the rearing period. To investigate the poorly understood evolution of role asymmetry in raptors at an intraspecific level, we videorecorded prey delivery and handling in 25 nests of the Eurasian kestrel, Falco tinnunculus, with prey types ranging in size from insects via lizards and mammals to birds, and simultaneously observed prey transfer from male to female outside the nest. As the nestlings aged, the male was more likely to allocate prey items directly to them for unassisted feeding, rather than to the female for further processing and feeding of the nestlings. This switch occurred earlier for lizards than mammals and birds, and earlier for smaller than larger mammals. The time needed to ingest a prey item decreased from birds via mammals to lizards, and was particularly short for insects. The switch from nestlings being fed dismembered prey to nestlings ingesting prey unassisted occurred earlier for lizards than mammals and birds, and earlier for smaller than larger mammals, while all insects were ingested unassisted. Thus, the female could be relieved from dismembering prey, and start hunting, earlier if all prey were lizards rather than mammals and birds, if all mammalian prey were smaller, and in particular if all prey were insects. Because providing for the family selects for small body size, extended confinement of the female as a sedentary food processor for offspring would leave greater potential for differential selection on male and female body size. This potential would vary geographically with the composition of the kestrel's diet, and be larger where the diet contains fewer insects and lizards and more mammals and birds.

As offspring grow, parents often feed them with different sizes or taxa of prey to suit the changing nutritional or energetic demands. We investigated whether such changes in prey types were innate and inflexible or whether they were based on the proximate cue of offspring size. We created experimental broods in which parent blue tits Cyanistes caeruleus and pied flycatchers Ficedula hypoleuca received either older nestlings simulating rapid development or younger nestlings simulating delayed development. The size of prey increased over time in all brood types, suggesting a strong programmed pattern of foraging by parents. However, delayed broods were provisioned with smaller prey than control or advanced broods indicating some plasticity in the response by the parents to the size of nestlings. Although female birds brought smaller prey than male birds, both sexes showed the same rate of increase of prey size with time and brought similar types of prey items. The proportion of soft, digestible larva prey in the nestling diet decreased over time in pied flycatchers but increased in blue tits. Counter to the hypothesis that spiders provide unique and preferred nutrients for young nestlings, the proportion of arachnids in the diet did not change with nestling age for either species. The lack of treatment effect on the taxa of prey delivered suggests that temporal shifts in diet composition are not driven by the proximate cues of nestling age or size but that the feeding patterns are fairly innate and fixed in these altricial birds.

Few studies have reported flight responses of prey on landscape slopes in the wild, and little theoretical work is available. We present a formal model to predict whether prey should move up or down the hillside after detecting a perched raptor as determined by the duration of the attack once launched by the predator, perching height of the predator, and the landscape slope. We recorded escape responses of blue tits Cyanistes caeruleus and great tits Parus major when approached by a human in the field. This was done in the postfledging period, when the demand for food is high, and when the families usually move to a new site, presumably perceived to be safer, to continue foraging after being exposed to a predator. We found that great tit families, which prefer to forage close to the ground, flew uphill, matching the model’s prediction. However, blue tit families, which forage higher in the canopy, did not move uphill but moved higher up in the trees. Vertical movement upward may be the safest option if the predator is located on the ground. Modeling escape flights may encourage detailed studies of attack and escape behaviors in animals and provide insights in predator–prey interactions in general.

© 2014 The Authors. Nests are structures built to support and protect eggs and/or offspring from predators, parasites, and adverse weather conditions. Nests are mainly constructed prior to egg laying, meaning that parent birds must make decisions about nest site choice and nest building behavior before the start of egg-laying. Parent birds should be selected to choose nest sites and to build optimally sized nests, yet our current understanding of clutch size-nest size relationships is limited to small-scale studies performed over short time periods. Here, we quantified the relationship between clutch size and nest size, using an exhaustive database of 116 slope estimates based on 17,472 nests of 21 species of hole and non-hole-nesting birds. There was a significant, positive relationship between clutch size and the base area of the nest box or the nest, and this relationship did not differ significantly between open nesting and hole-nesting species. The slope of the relationship showed significant intraspecific and interspecific heterogeneity among four species of secondary hole-nesting species, but also among all 116 slope estimates. The estimated relationship between clutch size and nest box base area in study sites with more than a single size of nest box was not significantly different from the relationship using studies with only a single size of nest box. The slope of the relationship between clutch size and nest base area in different species of birds was significantly negatively related to minimum base area, and less so to maximum base area in a given study. These findings are consistent with the hypothesis that bird species have a general reaction norm reflecting the relationship between nest size and clutch size. Further, they suggest that scientists may influence the clutch size decisions of hole-nesting birds through the provisioning of nest boxes of varying sizes.

Raptors are known for asymmetric parental roles, with the female brooding and feeding offspring, and the male providing food, usually assisted by the female from the latter part of the rearing period. Yet, the evolution of this role asymmetry is poorly understood. From filming prey delivery and handling in 61 nests of 9 raptor species, we show that the female role is related to prey size and prey type. Within species, nestlings were less likely to ingest larger prey unassisted, independent of increasing ability of unassisted feeding with increasing age. Feeding time increased with prey size and was longer for avian than for mammalian prey of the same size when nestlings fed unassisted. Across species, the female partitioned prey and fed offspring for a longer portion of the rearing period as prey size increased and as the diet contained more birds. Providing for the family selects for small body size; hence, extended female confinement as sedentary food processor for offspring would leave greater potential for differential selection on male and female body size. This may explain the female-biased size dimorphism among raptors, which becomes larger as diet changes from insects via reptiles and mammals to birds and as relative prey size increases. Symmetric parental roles and no female-biased size dimorphism would be expected in birds providing insects or other food that nestlings swallow without maternal assistance. Prey type and prey size would be important also for sexual conflicts and evolution of polygamy and mate desertion in birds providing for offspring.

Social learning is widely used among vertebrates to acquire information about a variable environment. We conducted a study of social learning in the wild which involved cross-fostering eggs of blue tits, Cyanistes caeruleus, to nests of great tits, Parus major, and vice versa. This allowed us to quantify the consequences of being reared in a different social context but in an environment otherwise natural to the birds. We studied choice of nest site by offering to the local recruits either a small or a large nestbox. Most blue tits bred in small nestboxes, whereas most great tits used the large boxes. Size of the natal nestbox affected subsequent box choice. In addition, in blue tits, more cross-fostered birds than controls nested in large nestboxes, with an opposite result for cross-fostered great tits. Apparently, as a consequence of sexual misimprinting on their foster parents, the cross-fostered young used members of the foster species as models for subsequent nest site choice. Such social copying may apply broadly to other types of behaviours and not only to the choice of nest site. This study demonstrates both vertical and horizontal transmission of nest site preference of two vertebrates in the wild. Future studies should try to find out how animals balance the use of personal experience with the information socially acquired.

Recent research on reproduction in animals has emphasized phenology and prey matching in the long term and on large spatial scales (e.g., linked to global climate change). We studied how individuals within one reproductive cycle and at small spatial scales may try to maximize access to food resources that vary in space and time. Herbivorous mammals are known to track favorable phenological stages of their food plants and move seasonally on the landscape. Whether phenology similarly affects spatial movements of birds on their breeding grounds is largely unknown. We studied postfledging movements of Blue Tits (Cyanistes caeruleus) and Great Tits (Parus major) when the young were escorted by parents during 19 to 43 days posthatching. This was done over 4 years in a 1.6-km2 woodland area in Norway in which an elevational gradient (105–266 m) caused a phenological delay in vegetation and peak abundance of caterpillar prey at the higher elevations. Postfledging movements were similar in the two tit sp...

In migratory birds, mistimed arrival might have negative consequences for individual fitness, causing population declines. This may happen if arrival time is not synchronized with breeding time, especially when earlier springs favour earlier reproduction. We studied spring arrival time to the breeding areas in a pied flycatcher Ficedula hypoleuca population in southern Norway during a 30-year period (1985–2014). We investigated trends in arrival both for the entire population and for different population fractions (e.g. early vs. late arrivals). We also studied sex and age class differences, along with repeatability of arrival. Finally, we explored how arrival is influenced by environmental conditions at the areas birds use throughout the year, using mixed-effects models and quantile regressions with individual-based data. Spring arrival advanced over five days, at a similar rate through the entire population. Males and adult birds arrived earlier than females and yearlings. Arrival was significantly repeatable for males and females. Birds arrived earlier in years with high temperature and rainfall at the breeding grounds, and low NDVI both on the Iberian Peninsula and in central Europe. Later fractions of the population showed a steeper response to these environmental variables. This intra-population heterogeneity in the responses to the environment probably stems from a combination between the different selection pressures individuals are subject to and their age-related experience. Our results highlight the importance of studying how migration phenology is affected by the environment not only on the breeding grounds but also on the other areas birds use throughout the year.

Marie Vaugoyeau [et al.], The increase in size of human populations in urban and agricultural areas has resulted in considerable habitat conversion globally. Such anthropogenic areas have specific environmental characteristics, which influence the physiology, life history, and population dynamics of plants and animals. For example, the date of bud burst is advanced in urban compared to nearby natural areas. In some birds, breeding success is determined by synchrony between timing of breeding and peak food abundance. Pertinently, caterpillars are an important food source for the nestlings of many bird species, and their abundance is influenced by environmental factors such as temperature and date of bud burst. Higher temperatures and advanced date of bud burst in urban areas could advance peak caterpillar abundance and thus affect breeding phenology of birds. In order to test whether laying date advance and clutch sizes decrease with the intensity of urbanization, we analyzed the timing of breeding and clutch size in relation to intensity of urbanization as a measure of human impact in 199 nest box plots across Europe, North Africa, and the Middle East (i.e., the Western Palearctic) for four species of hole-nesters: blue tits (Cyanistes caeruleus), great tits (Parus major), collared flycatchers (Ficedula albicollis), and pied flycatchers (Ficedula hypoleuca). Meanwhile, we estimated the intensity of urbanization as the density of buildings surrounding study plots measured on orthophotographs. For the four study species, the intensity of urbanization was not correlated with laying date. Clutch size in blue and great tits does not seem affected by the intensity of urbanization, while in collared and pied flycatchers it decreased with increasing intensity of urbanization. This is the first large-scale study showing a species-specific major correlation between intensity of urbanization and the ecology of breeding. The underlying mechanisms for the relationships between life history and urbanization remain to be determined. We propose that effects of food abundance or quality, temperature, noise, pollution, or disturbance by humans may on their own or in combination affect laying date and/or clutch size., E. Barba acknowledges funding of project CGL2013-48001-C2-1-P (Spanish Ministry of Science and Innovation).

International audience; Divergent sexual selection within allopatric populations may result in divergent sexual phenotypes, which can act as reproductive barriers between populations upon secondary contact. This hypothesis has been most tested on traits involved in precopulatory sexual selection, with less work focusing on traits that act after copulation and before fertilization (i.e., postcopulatory prezygotic traits), particularly in internally fertilizing vertebrates. However, postcopulatory sexual selection within species can also drive trait divergence, resulting in reduced performance of heterospecific sperm within the female reproductive tract. Such incompatibilities, arising as a by-product of divergent postcopulatory sexual selection in allopatry, can represent reproductive barriers, analogous to species-assortative mating preferences. Here, we tested for postcopulatory prezygotic reproductive barriers between three pairs of taxa with diverged sperm phenotypes and moderate-to-high opportunity for postcopulatory sexual selection (barn swallows Hirundo rustica versus sand martins Riparia riparia, two subspecies of bluethroats, Luscinia svecica svecica versus L. s. namnetum, and great tits Parus major versus blue tits Cyanistes caeruleus). We tested sperm swimming performance in fluid from the outer reproductive tract of females, because the greatest reduction in sperm number in birds occurs as sperm swim across the vagina. Contrary to our expectations, sperm swam equally well in fluid from conspecific and heterospecific females, suggesting that postcopulatory prezygotic barriers do not act between these taxon pairs, at this stage between copulation and fertilization. We therefore suggest that divergence in sperm phenotypes in allopatry is insufficient to cause widespread postcopulatory prezygotic barriers in the form of impaired sperm swimming performance in passerine birds.

Parent birds respond to a variety of cues from their offspring when provisioning them with food. Bright flange colours and large body size are two traits of offspring that many parents seem to favour, but little is known about how such traits interact. By experimentally altering the difference in mass between nestmates while concurrently blackening the flanges of either the large or small nestlings in the brood, we tested whether large body size could compensate for dull coloration. In three species of cavity nesters (northern flicker, Colaptes auratus, great tit, Parus major, and pied flycatcher, Ficedula hypoleuca), doubly disadvantaged offspring that were both small and dull performed the worst, whereas large and bright offspring received the most provisioning, consistent with the idea of additive effects. We used regression to show that, for flickers, dull (blackened) nestlings performed as well as bright nestlings when they were 20% larger than their bright nestmates. For passerines, dull nestlings had to be 30–40% larger than bright nestlings to receive equivalent amounts of food from parents. Within-brood differences in mass before manipulation were often greater than this size difference threshold, suggesting that hatching asynchrony has a stronger influence on food allocation than do colour differences among siblings.

In birds with bi-parental care, the provisioning link between prey capture and delivery to dependent offspring is regarded as often symmetric between the mates. However, in raptors, the larger female usually broods and feeds the nestlings, while the smaller male provides food for the family, assisted by the female in the latter part of the nestling period, if at all. Prey items are relatively large and often impossible for nestlings to handle without extended maternal assistance. We video-recorded prey delivery and handling in nests of a raptor with a wide diet, the Eurasian kestrel Falco tinnunculus, and simultaneously observed prey transfer from male to female outside the nest. The male selectively allocated larger items, in particular birds and larger mammals, to the female for further processing and feeding of nestlings, and smaller items, in particular lizards and smaller mammals, directly to the nestlings for unassisted feeding. Hence, from the video, the female appeared to have captured larger prey than the male, while in reality no difference existed. The female's size-biased interception of the male's prey provisioning line would maximize the male's foraging time, and maximize the female's control of the allocation of food between her own need and that of the offspring. The male would maximize his control of food allocation by capturing smaller prey. This conflict would select for larger dominant females and smaller energy-efficient males, and induce stronger selection the longer the female depends on the male for self-feeding, as a proportion of the offspring dependence period.

In altricial birds, parents are assumed to optimize the total food delivery to the brood given the time constraints set by self-feeding and food collecting. Older nestlings may require more food than younger ones, and nestlings may need more energy when their growth rate is higher. By video monitoring prey deliveries in ten nests of the Eurasian Kestrel (Falco tinnunculus), we examined whether parents adjusted feeding effort in relation to nestling age. Based on published data on the growth and energy intake of Kestrel nestlings, we predicted parental prey mass delivery to peak at a nestling age of 15–17 days. The prediction was supported. The decrease in provisioning rate during the later nestling stages was best explained by nestling age. However, we cannot be conclusive as to whether this was caused by a decrease in nestling food demand, or by a seasonal decrease in the availability of voles, the dominant prey. The change in provisioning was mostly an effect of a change in the number of prey items delivered. However, prey size also tended to decrease with increasing nestling age. This is opposite to what has been found in most non-raptorial altricial birds, and may have been caused by the ability of Kestrel parents to dismember large prey and thus overcome the gape size-restricted swallowing capacity of small nestlings, together with a need to provide smaller prey to older nestlings when they start to feed unassisted.

1. Climate warming has led to shifts in the seasonal timing of species. These shifts can differ across trophic levels, and as a result, predator phenology can get out of synchrony with prey phenology. This can have major consequences for predators such as population declines owing to low reproductive success. However, such trophic interactions are likely to differ between habitats, resulting in differential susceptibility of populations to increases in spring temperatures. A mismatch between breeding phenology and food abundance might be mitigated by dietary changes, but few studies have investigated this phenomenon. Here, we present data on nestling diets of nine different populations of pied flycatchers Ficedula hypoleuca, across their breeding range. This species has been shown to adjust its breeding phenology to local climate change, but sometimes insufficiently relative to the phenology of their presumed major prey: Lepidoptera larvae. In spring, such larvae have a pronounced peak in oak habitats, but to a much lesser extent in coniferous and other deciduous habitats. 2. We found strong seasonal declines in the proportions of caterpillars in the diet only for oak habitats, and not for the other forest types. The seasonal decline in oak habitats was most strongly observed in warmer years, indicating that potential mismatches were stronger in warmer years. However, in coniferous and other habitats, no such effect of spring temperature was found. 3. Chicks reached somewhat higher weights in broods provided with higher proportions of caterpillars, supporting the notion that caterpillars are an important food source and that the temporal match with the caterpillar peak may represent an important component of reproductive success. 4. We suggest that pied flycatchers breeding in oak habitats have greater need to adjust timing of breeding to rising spring temperatures, because of the strong seasonality in their food. Such between-habitat differences can have important consequences for population dynamics and should be taken into account in studies on phenotypic plasticity and adaptation to climate change.

We investigated whether a mechanism of gape size limitation could increase the competitive ability of a large brood parasite in a brood of smaller host nestlings. The gape size of hatchling birds may limit the size of prey they can swallow and hence parents should bring larger more profitable prey as their nestlings grow. The relatively large gape of a brood parasite in a brood of smaller hosts may 1) increase provisioning rate to the brood, 2) allow the parasite to swallow large prey, or 3) cause parents to start bringing larger prey at an earlier nestling stage. We added 1 large same-aged great tit Parus major nestling to broods of smaller blue tits Cyanistes caeruleus to simulate a naive brood parasite system and filmed them when 2–3 days old. The cue of a single large nestling did not cause parents to increase provisioning rates nor to change the species of prey, but prey items were larger than in control broods. Large prey were "tested" more often than small prey, that is offered and then removed from the gapes of small nestlings, and 17% of the prey that the great tit nestling received had been previously offered to a blue tit. Our results revealed that prey size brought by parents could further increase the competitive ability of brood parasites.

To study the ecological and evolutionary effects of climate change on timing of annual events, scientists need access to data that have been collected over long time periods. High-quality long-term phenology data are rare and costly to obtain and there is therefore a need to extract this information from other available data sets. Many long-term studies on breeding birds include detailed information on individually marked parents and offspring, but do not include information on timing of breeding. Here, we demonstrate how a study of repeated standard measurements of white-throated dipper Cinclus cinclus nestlings in our study system in southernmost Norway can be used for modeling nestling growth, and how this statistical model can be used to estimate timing of breeding for birds with sparser data. We also evaluate how the accuracies of nestling growth models based on different morphological traits (mass and feather length) differ depending on the nestling age, present user guidelines and demonstrate how they can be applied to an independent data set. In conclusion, the approach presented is likely to be useful for a wide variety of species, even if the preferred measurement may differ between species.

The initial evolutionary electromagnetic steps in the history of brain development are still unknown, although such knowledge might be of high relevance in understanding human degenerative diseases. All prokaryote organisms, one-celled or multicellular, must have an inherited system to process and store information activating instincts and reflexes, in order to give a quick response to external stimuli. We argue that magnetite is an obvious compound to be evaluated as an initial precursor from prebiotic Earth history in the evolution of such a system. Magnetite is a stable ferrimagnetic compound, present in organisms ranging from bacteria to humans. It occurred naturally in the early Earth environment and was later synthesized de novo in biotic organisms. We suggest that the use of magnetite has evolved to represent the main storage system for learned memory in all organisms living today.

Steen R., Low L.M., Sonerud G.A., Selas V. & Slagsvold T. 2011. Prey delivery rates as estimates of prey consumption by Eurasian Kestrel Falco tinnunculus nestlings. Ardea 99: 1–8.

The colour of blue-green bird eggs has been hypothesized to signal female quality to attending males, who may adjust their level of investment in the brood accordingly. The hypothesis has gained support in studies of Spanish pied flycatchers Ficedula hypoleuca. We performed a cross-fostering experiment in a Norwegian population of pied flycatchers to provide an independent test of the sexually selected egg colour hypothesis in this species. Egg colour was not significantly correlated with estimates of female quality (clutch size, average egg volume, first egg laying date and feeding rate). There was a significant decrease in chroma and increase in brightness and egg volume during the laying sequence, with some marked differences between six-egg and seven-egg clutches that might reflect differences in female quality. However, we found no significant influence of egg colour (foster or original clutch) on male feeding rate or offspring viability (hatching success, average mass and fledging success) and no significant difference in feeding rate for males with six-egg and seven-egg foster or original clutches. We conclude that Norwegian male pied flycatchers do not use egg colour as a cue to female quality, thus questioning the generality of previous support for the sexually selected egg colour hypothesis from this species.

Supplementary feeding of wild birds during winter is one of the most popular wildlife management activities, and is likely to have profound influence on the behavioural ecology of a species. At garden bird feeders, birds are now often fed well into the breeding season. Providing food within an established songbird territory, however, is likely to influence the territorial behaviour of the resident male. We used song performance during the dawn chorus in early spring to study behavioural changes in food-supplemented great tits, Parus major. After 2 weeks of continuous food supply within their territory, supplemented males started dawn singing later than control males, and thus postponed their regular dawn chorus before sunrise. This effect was maintained 2 weeks after food supplementation had ended. However, we did not find an effect of long-term feeding on song output. Our results were largely unexpected because formal models and field studies on short-term food supplementation suggested an earlier start of dawn singing or a higher dawn song output. Because we did not observe great tits visiting the feeders before sunrise or food supplementation increasing the numbers of conspecific intruders, the reasons for the delay in the start of dawn singing remain unclear; possible explanations include the presence of predators at feeding stations and the quality of the supplementary food itself. Delaying dawn singing could potentially affect the reproductive success of supplemented males, for example if females base extrapair mating decisions on dawn song performance of their mates.

In some songbird species, large song repertoires are advantageous in female attraction, whereas song sharing with neighbours may give an advantage in male‐male competition. Open-ended learners, with the ability to memorize new song elements throughout their lives, may learn from territorial neighbours and thus benefit from increasing both repertoire size and song sharing. A distinction needs to be made between true adult song learning, i.e. memorization of novel song elements, and vocal plasticity resulting in changes in the use of previously memorized elements, such as the use of hidden repertoires or increased production of previously rare syllable types. We assessed the ability of adult pied flycatcher Ficedula hypoleuca males to learn previously unheard song elements and to change their song production in response to playback of unfamiliar, conspecific song, emulating a singing neighbour. After a 1-week playback treatment, three out of 20 subjects had learned foreign song elements, providing evidence from the wild that pied flycatchers are true open-ended learners. However, the syllable sharing with the playback stimulus repertoires had not changed, and the males’ repertoires had decreased rather than increased. Hence, we did not find support for increased syllable sharing with neighbours or increased repertoire size as functions of adult song learning in pied flycatchers. Because pied flycatcher song seems to serve mainly for mate attraction, copying of attractive syllable types is a possible alternative function of adult song learning in this species.

Summary 1. Climate change may have profound consequences for many organisms. We have studied fluctuations in a population of the white-throated dipper Cinclus cinclus during 31 years (1978–2008) in a river system in southern Norway in relation to both large-scale and local weather conditions occurring during the non-breeding season. 2. Multiple regression and partial least squares regression were used to model the growth rate of the population, accounting for population size in the previous year. 3. Population growth was influenced by North Atlantic Oscillation (NAO), mean winter temperature, precipitation and timing of ice formation on the main lake in the river system in autumn. These variables explained 84% of the variation in population growth over the 31 -year study period. 4. Local winter conditions played a prominent role in explaining the population fluctuations, which is plausible because the dipper depends on open water for foraging. In the study area, winters can be harsh and rivers and lakes may freeze and severely affect the subsequent population size of the dipper in spring. 5. The breeding population of the dipper does not seem yet to have reached a level where all possible territories in the area have been occupied, even after mild winters, and the estimated carrying capacity is also decidedly lower (66 breeding pairs) than the number of available territories. If the trend of milder winters continues, the population might increase in the future. However, strong climate variation is expected to continue in the future, and hence periods of rapid growth of the dipper population will probably be followed by severe declines.

Most raptors take large prey for their size compared to other birds, but tear the prey apart into small morsels before swallowing. Little is known about how the efficiency of this prey handling varies among raptors, and how it relates to their feeding niches, diets and gape dimensions. We offered 202 mammalian and 224 avian prey items to 37 wild raptors kept temporarily in captivity, representing ten species and three orders. Feeding efficiency was measured as the proportion of a prey item that was ingested. The proportion of a prey item ingested was larger for mammalian than for avian prey, declined with prey size, increased with raptor size, and was larger for typical vole feeders (with shorter and wider bills) than typical bird feeders (with longer and narrower bills). The proportion of a prey item ingested was not related to raptor sex when controlling for focal raptor body mass. The probability that the head of a prey was ingested was higher if the prey was a mammal than if it was a bird, whereas the opposite was the case for the entrails of a prey. The results suggest that the traditional use of prey remains to estimate raptor diets may lead to severe biases, the magnitude of which would depend on prey type and size, raptor sex, species and order, and raptor feeding niche. Failure to correct for uneaten remains of a prey would lead to overestimating the profitability of large prey, and in particular of large avian prey. The results are consistent with the idea that vole feeders can afford to have a well-developed digestive tract, and thus swallow prey in large pieces, because they pounce on prey from above. Bird feeders, however, must ingest food in smaller pieces because they have smaller guts as a result of selection to keep the body mass low to capture agile prey.

Predictions of game theory models about the outcome of animal conflicts have most often been tested using male contests for mates, territories or food. We studied female contests for nest sites and mates in the pied flycatcher, Ficedula hypoleuca, and asked which factors affect the outcome and duration of the contests. Conflicts over residency were experimentally induced, but natural cases in which both females regarded themselves as owners were also included in the analyses. The ensuing escalated contests involved physical fighting, defence of the nestbox of the male and alarm calling. Contrary to expectations from game theory, fighting seemed to occur most often at the start of conflicts, whereas alarm calling occurred towards the end and nestbox visits throughout the conflict. The outcome of the contests was not determined by asymmetries in body size or age, nor by a simple previous-present owner asymmetry. Instead, it depended on the relative residence times of the opponents. The duration of the contests tended to increase with decreasing asymmetry in the residence times of females, whereas body size asymmetries had no influence. Because there is intense competition between females for a mate in the pied flycatcher, we suggest that females do not respect asymmetries in residency and body size, but fight in relation to the value of the mating opportunity. In particular, we point to the possibility that the value of a mating opportunity may increase with residence time because knowledge of other mating options may become outdated.

In several papers, it has been argued that two migratory species, the pied and the collared flycatcher, Ficedula hypoleuca and F. albicollis, take clutch size of a resident bird, the great tit Parus major, into account when deciding which of two adjacent nest boxes to use for their own breeding attempt (see Forsman et al. 2017). We termed this the interspecific cue hypothesis (the ICH; Slagsvold and Wiebe 2017) and argued that some of its basic assumptions have never been critically examined. Samplonius (2017) and Forsman et al. (2017) criticize our paper and argue that the ICH is the most plausible explanation but here we conclude that the new data they provide on the behaviour of the pied flycatcher (Forsman et al. 2017) are, in fact, inconsistent with the most critical assumption of the ICH. Therefore, the hypothesis should be rejected. This article is protected by copyright. All rights reserved.