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Specialist individuals within animal populations have shown to be more efficient foragers and/or to have higher reproductive success than generalist individuals, but interspecific reproductive consequences of the degree of diet specialisation in vertebrate predators have remained unstudied. Eurasian pygmy owls (hereafter POs) have less vole‐specialised diets than Tengmalm's owls (TOs), both of which mainly subsist on temporally fluctuating food resources (voles). To test whether the specialist TO is more limited by the main prey abundance than the generalist PO, we studied breeding densities and reproductive traits of co‐existing POs and TOs in central‐western Finland during 2002–2019. Breeding densities of POs increased with augmenting densities of voles in the previous autumn, whereas breeding densities of TOs increased with higher vole densities in both the previous autumn and the current spring. In years of vole scarcity, PO females started egg‐laying earlier than TOs, whereas in years of vole abundance TO females laid eggs substantially earlier than PO females. The yearly mean clutch size and number of fledglings produced of both POs and TOs increased with abundance of voles in the current spring. POs laid large clutches and produced large broods in years of both high and low vole abundance, whereas TOs were able to do so only in years of high vole abundance. POs were able to raise on average 73% of the eggs to fledglings whereas TOs only 44%. The generalist foraging strategy of POs including flexible switching from main prey to alternative prey (small birds) appeared to be more productive than the strictly vole‐specialized foraging strategy of TOs. In contrast to earlier studies at the individual‐level, specialist predators at the species level (in this case TOs) appear to be less effective than generalists (POs), but diet specialisation was particularly costly under conditions when scarcity of main foods limited offspring production.

In a substantial number of species, females show some development of secondary sexual characters. These traits can function as signals of individual phenotypic or genetic qualities and status to conspecifics. Individuals may benefit potentially from expressing signals or badges of status if they are reliable and honest signals of individual quality. In many species, badge sizes have been shown to correlate with dominance rank, which may be mediated by testosterone (T) levels. Here, we explored geographic variation in the size and properties of the white wing patch of female pied flycatchers Ficedula hypoleuca and its relation to circulating T levels in three populations (two southern populations in central Spain and a northern population in Finland). Furthermore, we aimed at detecting if the size of the white wing patch and its ultraviolet (UV) reflectance indicate individual quality. We found that females in Spain had larger, brighter and more UV reflecting wing patches than those in Finland. Females with higher UV reflectance and larger primary white patches bred earlier. Younger females and females with larger primary white wing patches showed higher T levels. In contrast, higher values of UV reflectance in feathers from these patches were associated with low T levels. Despite genetic differentiation and differences in trait expression between populations, female pied flycatchers from different populations may converge and use the size of white wing patches to signal their T levels and thereby their social dominance., This study was financed by project CGL2013-48193-C3-3-P to JM from Spanish Ministerio de Economía y Competitividad (MINECO).

Mothers may affect the future success of their offspring by varying allocation to eggs and embryos. Allocation may be adaptive based on the environmental conditions perceived during early breeding. We investigated the effects of food supplementation and predation risk on yolk hormone transfer in the pied flycatcher Ficedula hypoleuca. In a food supplementation experiment, females were food-supplemented prior to and during egg-laying and androgen concentrations were measured throughout the laying order. Predation risk was investigated in three different studies combining both correlative data, where flycatchers bred in close proximity to two different predator species that prey upon adult flycatchers (either Tengmalm's owl Aegolius funereus or pygmy owl Glaucidium passerinum), and an experimental manipulation, where flycatchers were exposed to cues of a nest predator (least weasel Mustela nivalis). Females receiving food supplementation laid eggs with lower concentrations of androstenedione (A4) than females not receiving food supplements. Yolk testosterone (T) concentration showed the same pattern but the difference was not statically significant. Testosterone (but not A4) concentration increased within clutches, from the first to the last egg, independently of the food supplementation. Females breeding under high predation risk did not differ from control females in their yolk androgen levels (A4, T or progesterone). However, concentrations of A4 tended to be lower in the proximity of pygmy owls, which could indirectly increase offspring survival after fledging. Food supplementation during egg-laying seems to have a stronger impact on maternal transfer of androgens than predation risk. Food availability and predation risk could differentially affect the trade-offs of androgen allocation for the offspring when raised in good vs. dangerous environments.

Understanding what drives or prevents long-distance migrants to respond to environmental change requires basic knowledge about the wintering and breeding grounds, and the timing of movements between them. Both strong and weak migratory connectivity have been reported for Palearctic passerines wintering in Africa, but this remains unknown for most species. We investigated whether pied flycatchers Ficedula hypoleuca from different breeding populations also differ in wintering locations in west-Africa. Light-level geolocator data revealed that flycatchers from different breeding populations travelled to different wintering sites, despite similarity in routes during most of the autumn migration. We found support for strong migratory connectivity showing an unexpected pattern: individuals breeding in Fennoscandia (S-Finland and S-Norway) wintered further west compared to individuals breeding at more southern latitudes in the Netherlands and SW-United Kingdom. The same pattern was found in ring recovery data from sub-Saharan Africa of individuals with confirmed breeding origin. Furthermore, population-specific migratory connectivity was associated with geographical variation in breeding and migration phenology: birds from populations which breed and migrate earlier wintered further east than birds from late' populations. There was no indication that wintering locations were affected by geolocation deployment, as we found high repeatability and consistency in C-13 and N-15 stable isotope ratios of winter grown feathers of individuals with and without a geolocator. We discuss the potential ecological factors causing such an unexpected pattern of migratory connectivity. We hypothesise that population differences in wintering longitudes of pied flycatchers result from geographical variation in breeding phenology and the timing of fuelling for spring migration at the wintering grounds. Future research should aim at describing how temporal dynamics in food availability across the wintering range affects migration, wintering distribution and populations' capacity to respond to environmental changes.

The hormonal environment during early development, such as maternally derived androgens in bird eggs, has been shown to shape offspring in ways that may have important short- and long-term consequences for phenotype and behavior. However, studies on the effects of androgens on begging behavior and growth in birds have provided variable results and sex-specific effects are not well understood. We experimentally elevated yolk androgen levels in whole clutches in a passerine bird, the pied flycatcher Ficedula hypoleuca and studied effects on male and female begging behavior, ingestion and digestion. Yolk androgen elevation led to shorter latencies to beg in both male and female nestlings but to greater begging rates only in males. Both responses could be used as cues to solicit more food from parents. Yolk androgens had no effect on food intake, fecal wet mass or fecal water content. However, the proportion of organic matter in feces was lower in androgen-treated than control males, potentially suggesting that the androgen-treated individuals had more efficient digestion. We discuss the alternative pathways of effects of yolk androgens on begging, growth and digestion. If the effects of yolk androgens on phenotype and behavior are causally linked, there is less scope for the mother to adjust specific offspring traits independently from other traits. The sex-specific effects of yolk androgens should be studied more, also in within-clutch context, as the costs and benefits for each sex may further differ in relation to hatching order.

The expression and impact of maternal effects may vary greatly between populations and environments. However, little is known about large-scale geographical patterns of variation in maternal deposition to eggs. In birds, as in other oviparous animals, the outermost maternal component of an egg is the shell, which protects the embryo, provides essential mineral resources and allows its interaction with the environment in the form of gas exchange. In this study, we explored variation of eggshell traits (mass, thickness, pore density and pigmentation) across 15 pied flycatcher populations at a large geographic scale. We found significant between-population variation in all eggshell traits, except in pore density, suggesting spatial variation in their adaptive benefits or in the females' physiological limitations during egg laying. Between- population variation in shell structure was not due to geographic location (latitude and longitude) or habitat type. However, eggshells were thicker in populations that experienced higher ambient temperature during egg laying. This could be a result of maternal resource allocation to the shell being constrained under low temperatures or of an adaptation to reduce egg water loss under high temperatures. We also found that eggshell colour intensity was positively associated with biliverdin pigment concentration, shell thickness and pore density. To conclude, our findings reveal large- scale between-population variation of eggshell traits, although we found little environmental dependency in their expression. Our findings call for further studies that explore other environmental factors (e.g. calcium availability and pollution levels) and social factors like sexual selection intensity that may account for differences in shell structure between populations., This study was financially supported by the former Spanish Ministerio de Innovación y Ciencia (projects CGL2007-61251/BOS and CGL2010-19233-C03-02 to JM, and contract ‘Junta para la Ampliación de Estudios’ to JM, funded by the Spanish Research Council-CSIC and the European Social Fund), Emil AaltonenFoundation in Finland (grant to TL), Finnish Cultural Foundation (grant to SR), Academy of Finland (project 8119367 to TE). EB was financed by a grant for Scientific Schools (NSh-5325.2012.4). Data collection in Moscow region was supported by Russian Fund of Basic Researches (RFBR) and Russian Ministry of Education. RM and VT were supported by the Estonian Ministry of Education and Science (project 0180004s09) and the European Regional Development Fund (Center of Excellence FIBIR).

Predation risk is an environmental stressor that can induce changes in prey behavior and physiology. Perception of predation risk may indirectly aff ect off spring traits and future fi tness prospects via impacts on the condition of parents. Females may infl uence the survival of their off spring via maternal eff ects, especially when breeding in stressful conditions. We investigated the eff ects of continuous predation risk perceived by mothers on the maternal allocation of immune factors and carotenoids in eggs of the pied fl ycatcher Ficedula hypoleuca . We collected eggs from wild pied fl ycatchers that bred in the vicinity of a predator nest (pygmy owl Glaucidium passerinum ), were exposed to cues of a mammalian nest predator (urine of least weasel Mustela nivalis ), or received appropriate controls for these two groups. Pied fl ycatchers transferred more immunoglobulin in eggs under high predation risk in both owl and mammalian predator treatments. Th e presence of owl nests also lowered the level of lysozyme transferred in the eggs in one of the two study years. Predation risk did not modify egg size or overall carotenoid levels. Our results show that continuous predation risk perceived by females during egg-laying aff ects egg composition. Th is diff erent allocation of maternal immune factors may be an adaptive response evolved to increase the probability of off spring survival.

Costs and benefits of dispersal can vary in space and time, depending on environmental factors and individual state. Plastic, condition-dependent dispersal strategies, in which individuals rely on external cues such as food abundance to adjust their dispersal distances, are therefore expected to evolve in temporally fluctuating environments. We examined factors affecting breeding dispersal distances in Eurasian kestrels Falco tinnunculus subsisting on multi-annually and cyclically fluctuating voles as their main food. We attempted to avoid traditional bias in dispersal studies by having large study areas and by taking detection probabilities into account. We observed 320 dispersal events of male and 215 events of female kestrels from our study areas in western Finland during 24 yr. After correcting for distance-specific detection probability, the estimates of mean dispersal distances increased two-fold being still clearly higher for females than males. Vole abundance in the spring of settlement was more important in determining average dispersal distances than vole abundance in the previous autumn. At the population level (cross-sectional model), both males and females dispersed longer distances when the spring abundance of their main food (voles) was low compared to when it was abundant, as predicted by the food depletion hypothesis. At the individual level (longitudinal model), only females responded to the food situation by dispersing more when food abundance was low in the spring of settlement. Females also dispersed longer when vole abundance in the previous autumn had been high. Individual males did not respond to vole abundance, which implies that the population level response in males might have been caused by long-distance dispersers, which breed in the study area only in good vole years. Our results show that the dispersal distances of kestrels at northern latitudes depend both on individual properties (gender, age, and possibly individual tendency to disperse) and environmental conditions (temporal variation in main food abundance).

Large-scale climate fluctuations, such as the North Atlantic Oscillation (NAO), have a marked effect on the timing of spring migration of birds. It has however been suggested that long-distance migrants wintering in Africa could respond less to NAO than short-distance migrants wintering in Europe, making them more vulnerable to climatic changes. We studied whether migratory boreal and arctic bird species returning from different wintering areas show differences in responses to the NAO in the timing of their spring migration. We used data on 75 species from two bird observatories in northern Europe (60°N). By extending the examination to the whole distribution of spring migration and to a taxonomically diverse set of birds, we aimed at finding general patterns of the effects of climate fluctuation on the timing of avian migration. Most species arrived earlier after winters with high NAO index. The degree of NAO-response diminished with the phase of migration: the early part of a species’ migratory population responded more strongly than the later part. Early phase waterfowl responded strongest to NAO, but in later phases their response faded to non-significant. This pattern may be related to winter severity and/or ice conditions in the Baltic. In the two other groups, gulls and waders and passerines, all phases of migration responded to NAO and fading with phase was non-significant. The difference between waterfowl and other groups may be related to differences between the phenological development of their respective macrohabitats. Wintering area affected the strength of NAO response in a complicated way. On average medium distance migrants responded most strongly, followed by short-distance migrants and partial migrants. Our results concerning the response of long-distance migrants were difficult to interpret: there is an overall weak yet statistically significant effect, but patterns with phase of migration need further study. Our results highlight the importance of examining the whole distribution of migration and warrant the use of data sets from several sampling sites when studying climatic effects on the timing of avian life-history events.