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For many years, eggs of diverse bird species have been used as monitoring tools in studies investigating perfluoroalkyl substances (PFAS) contamination, especially in marine and remote areas. Avian eggs are a suitable monitoring matrix because they are relatively easy to collect and their yolks store diverse maternally transferred PFAS. Moreover, the concentrations of PFAS detected in the eggs are a good proxy for maternal exposure and allow the assessment of the potential risk for birds. These features support the use of avian eggs as a key monitoring tool in exposure assessment of PFAS-contaminated sites. We first review the recent application of avian eggs in PFAS monitoring in environmental risk assessment schemes, highlighting strengths and limitations and suggesting which criteria should be considered when selecting a proper study species and structuring the sampling and analytical protocol. Eventually, we report findings from a field study realized in 2020 near a perfluoropolymer factory site in the upper Po plain (Northern Italy), revealing an unprecedented contamination level of PFOA and C6O4 in three species of wild passerines. In future, long-term monitoring of PFAS contamination using avian eggs should be maintained, to provide crucial information on the temporal trend of fluorochemical production and waste disposal, while facilitating early identification of emerging PFAS as well as the quantification of their biomagnification across the trophic web. Integr Environ Assess Manag 2021;17:733–745. © 2021 SETAC.

Female promiscuity can function to acquire both direct and indirect benefits from their social mate and extra-pair males. In many raptor species, intense mate-feeding significantly contributes to female energy requirements before and during egg laying. Moreover, females may use mate-feeding effort to assess male quality. In this study of the lesser kestrel Falco naumanni, we aimed at experimentally manipulating the female's perception of mate quality by providing females with extra food during egg laying, and evaluated the occurrence of extra-pair paternity in food-supplemented and control broods by parentage analyses. No extra-pair offspring (EPO) was found among 19 food-supplemented broods, whereas EPO occurred in five out of 17 control broods. No significant differences in morphological traits, body condition and reproductive success were found between faithful and unfaithful females. However, clutches containing EPO were laid later in the breeding season. Moreover, un-cuckolded males had longer tarsi than cuckolded ones, indicating larger body size. Hence, extra food provisioning and early breeding reduced the occurrence of EPO in lesser kestrels. In addition, we confirmed the occurrence of intraspecific brood parasitism, as five nestlings were not the offspring of the brooding female. The results of our food-provisioning experiment support the idea that mate-feeding ability is a reliable indicator of male quality, and are in accordance with the hypothesis that male mate-feeding behaviour is a sexually selected trait.

Background. Microbial communities are found on any part of animal bodies exposed to the environment, and are particularly prominent in the gut, where they play such a major role in the host metabolism and physiology to be considered a ''second genome''. These communities, collectively known as ''microbiome'', are well studied in humans and model species, while studies on wild animals have lagged behind. This is unfortunate, as different studies suggested the central role of the gut microbiome in shaping the evolutionary trajectories of species and their population dynamics. Among bird species, only few descriptions of raptor gut microbiomes are available, and mainly carried out on captive individuals. Objectives. In this study, we aimed at improving the knowledge of raptor microbiomes by providing the first description of the gut microbiome of the lesser kestrel (Falco naumanni), a cavity-nesting raptor. Results. The gut microbiome of the lesser kestrel was dominated by Actinobacteria (83.9%), Proteobacteria (8.6%) and Firmicutes (4.3%). We detected no differences in microbiome composition between males and females. Furthermore, the general composition of the microbiome appears similar to that of phylogenetically distant cavity-nesting species. Conclusions. Our results broaden the knowledge of raptor gut microbial communities and let us hypothesize that the distinct nest environment in terms of microclimate and presence of organic material from previous breeding attempts, to which cavity-nesting species that reuse the nest are exposed, might be an important driver shaping microbiomes.

Marmora’s Warbler (Curruca sarda) and Balearic Warbler (C. balearica) are allopatric sibling species and were recently split mostly based on morphological and ethological characteristics. Here we provide the first phylogenetic and phylogeographic analyses of this species complex to support the taxonomic status of C. sarda and C. balearica in light of integrative taxonomy. We sampled the two taxa in most of their breeding ranges and we sequenced three mitochondrial and one nuclear gene region. All C. balearica individuals had private haplotypes for the four markers and formed monophyletic clades. Genetic distances between the two taxa were comparable with those found between other species belonging to the Curruca genus. Furthermore, most of the genetic variance was expressed at the interspecific level, rather than between different populations within taxa or between individuals within populations. Our results strongly support the current taxonomic status of these two warblers as distinct species.

We provide the first-ever investigation of feather microbiota by high throughput DNA sequencing for any bird species by describing bacteria found on the innermost tertial feather of 22 adult common swifts (Apus apus). We found feather microbiomes with large abundance of Bacillales, Actinomycetales, Burkholderiales, Sphingobacteriales, Sphingomonadales, Rhizobiales, Pseudomonadales, Clostridiales, Rubrobacterales and Lactobacillales. Bacterial communities did not change with any feature of individual swifts. Network and cluster analysis of feather microbiomes disclosed three clusters, characterized by bacteria typical of seawater, plants and soil and unrelated to conditions at the breeding grounds. We hypothesize that feather microbiomes reflect, at least partly, airborne bacterial communities of the environments where individuals spent non-breeding periods, or of those that they crossed during migration, rather than breeding environment. If confirmed, this evidence may disclose the possibility to use feather bacteria as proxies for tracing non-breeding origin and routes of migratory birds.

Individuals often considerably differ in the timing of their life-cycle events, with major consequences for individual fitness, and, ultimately, for population dynamics. Phenological variation can arise from genetic effects but also from epigenetic modifications in DNA expression and translation. Here, we tested if CpG methylation at the poly-Q and 5′-UTR loci of the photoperiodic Clock gene predicted migration and breeding phenology of long-distance migratory barn swallows (Hirundo rustica) that were tracked year-round using light-level geolocators. Increasing methylation at Clock poly-Q was associated with earlier spring departure from the African wintering area, arrival date at the European breeding site, and breeding date. Higher methylation levels also predicted increased breeding success. Thus, we showed for the first time in any species that CpG methylation at a candidate gene may affect phenology and breeding performance. Methylation at Clock may be a candidate mechanism mediating phenological responses of migratory birds to ongoing climate change.

Microbiomes can be considered as 'second genomes' for the host, and can deeply affect its physiology, behaviour and fitness. We investigated the cloacal microbiomes (CMs) of adult and nestling barn swallows (Hirundo rustica), a small insectivorous migratory passerine bird, in order to assess whether CM structure was related to major ecological traits of individuals. Illumina sequencing of the V5-V6 hypervariable regions of the bacterial 16S rRNA gene showed that barn swallow CMs were dominated by Proteobacteria, Firmicutes, Actinobacteria, Tenericutes and Bacteroidetes. Nestling CMs were more similar to one another than adult ones, but showed higher alpha diversity. Sibling nestlings had more similar CMs than non-sibling ones. CMs of adult males also differed from those of adult females, but pair members had more similar CMs than expected by chance. In contrast, CMs did not differ between male and female nestlings. Finally, in adults, CMs strongly different from the 'average' CM were associated to lower survival prospects of the host. The CMs of a bird species in the wild are therefore related to important traits of individuals, such as survival, suggesting that microbiomes should be included among the traits examined in ecological studies.

Light-level geolocators are currently widely used to track the migration of small-sized birds, but their potentially detrimental effects on survival of highly aerial species have been poorly investigated so far. We recorded capture–recapture histories of 283 common swifts Apus apus and 107 pallid swifts Apus pallidus breeding in 14 colonies in Italy, Spain, Sweden and Switzerland that were equipped with 10 different types of geolocators (‘geolocator birds’), and compared their survival with that of, respectively, 215 common and 101 pallid swifts not equipped with geolocators (‘control birds’). Data were analysed using both GLMMs with return rate as a proxy for survival and mark–recapture models to estimate survival while accounting for recapture probability. In all the analyses, geolocator birds showed reduced apparent survival compared to controls. Geolocator weight was always lower than 3% of body mass, and did not affect survival per se. Geolocators with a light-stalk, which is used in some geolocator models to reduce light sensor shading by feathers, decreased apparent survival more than models without light-stalk. Apparent survival of geolocator birds significantly varied among sites, being much higher in northern Europe. Despite in our analyses we could only partly account for variable recapture probabilities among sites and for inter-annual variability in survival, our results generally showed that equipping swifts with geolocators decreased their survival prospects, but also that the magnitude of this effect may depend on species-specific traits. These conclusions are in line with those of other studies on aerial foragers. We suggest that future studies tracking the movements of aerial insectivorous birds should use devices designed to minimize drag.

Bird gut microbiota shows large variation among geographical populations of the same species–probably because, differently from mammals, gut microbiota of birds is largely affected by extrinsic factors such as diet and environmental conditions. We analysed the cloacal microbiota (CM) of 12 barn swallows (Hirundo rustica) from a colony in Northern Italy by high-throughput DNA sequencing of the 16S rRNA gene. The CMs, dominated by bacteria of the phyla Proteobacteria, Actinobacteria, Firmicutes and Bacteroidetes, did not significantly differ between adult females, adult males and fledglings. This first description of barn swallow CM in Italy, together with two previous studies from Europe, suggests that CMs of geographically different barn swallow populations are dominated by bacteria belonging to the same phyla but different genera. The intra-colony similarity of the CMs may be due to the exposure of individuals to the same local environmental conditions while on their breeding grounds.

Circannual rhythms often rely on endogenous seasonal photoperiodic timers involving 'clock' genes, and Clock gene polymorphism has been associated to variation in phenology in some bird species. In the long-distance migratory barn swallow Hirundo rustica, individuals bearing the rare Clock allele with the largest number of C-terminal polyglutamine repeats found in this species (Q8) show a delayed reproduction and moult later. We explored the association between Clock polymorphism and migration scheduling, as gauged by light-level geolocators, in two barn swallow populations (Switzerland; Po Plain, Italy). Genetic polymorphism was low: 91% of the 64 individuals tracked year-round were Q7/Q7 homozygotes. We compared the phenology of the rare genotypes with the phenotypic distribution of Q7/Q7 homozygotes within each population. In Switzerland, compared to Q7/Q7, two Q6/Q7 males departed earlier from the wintering grounds and arrived earlier to their colony in spring, while a single Q7/Q8 female was delayed for both phenophases. On the other hand, in the Po Plain, three Q6/Q7 individuals had a similar phenology compared to Q7/Q7. The Swiss data are suggestive for a role of genetic polymorphism at a candidate phenological gene in shaping migration traits, and support the idea that Clock polymorphism underlies phenological variation in birds.

Adaptive strategies of sex allocation functioning to increase fitness, including strategic allocation of sex in relation to birth order and sex composition of the progeny, have frequently been explored, but the development of a statistical framework for these analyses has lagged behind. In this paper, we contribute to filling this gap by devising a method for analyzing sex sequences based on a proper parameterization of generalized linear mixed models (GLMMs). The method is highly flexible and can be easily extended to investigate sequences of traits or events or other longitudinal data. As a worked example, we focus on the analysis of sex sequences of offspring produced by females in a single reproductive event and develop a method that allows analyzing simultaneously sequences of different length (e.g., clutches of different size) and sequences with missing data, as may frequently happen in "real-world" data sets. Different patterns of allocation among traits or events along the sequence were investigated, and a real data base of sex sequences of eclectus parrots (Eclectus roratus) fledglings produced by different females was analyzed. A tutorial for running the analyses with the R or the SAS software is provided in the Electronic Supplementary Material. © 2014 Springer-Verlag Berlin Heidelberg.

Variation in wing morphology results from the combination of diverse selection pressures. Wing feather morphology within species varies with sex and ontogenetic effects, and also with ecological factors. Yet, the direction of causation for the wing morphology–ecology association remains to be elucidated. Under the ‘ecology-dependence’ hypothesis, wing morphology covaries with ecological conditions, because the latter affect feather molt. Alternatively, the ‘habitat choice’ hypothesis posits that individuals with different wing morphology choose different habitats because of the habitat-dependent advantages of a specific wing morphology. We tested these competing hypotheses in the migratory, aerially insectivorous barn swallow (Hirundo rustica). We quantified wing morphology (isometric size, pointedness, and convexity) on the same individuals during consecutive breeding seasons (i.e., before and after molt in sub-Saharan wintering areas) and located wintering areas using light-level geolocators. Wing pointedness of females but not males during 1 year negatively correlated with vegetation vigor (gauged by the Normalized Difference Vegetation Index; NDVI) in the African area where individuals spent the next winter. Partial least-squares path modelling showed that the association between wing morphology and NDVI was sex-dependent. Conversely, NDVI during wintering did not predict wing morphology in the next breeding season. Because wing morphology can have carry-over effects on subsequent performance, we investigated selection on wing traits and found strong positive fecundity selection on wing size of females. Our results suggest that female barn swallows choose their wintering habitat depending on their wing morphology. In addition, directional fecundity selection operates on females, suggesting sex-dependence of current selection on the flight apparatus

Reproductive promiscuity, whereby females are fertilized by extrapair mates, is common. The frequency of extrapair fertilizations (EPFs) depends on at least three sources of variation. First, females may differ in their proneness to being fertilized by extrapair males. Second, males may differ in traits that affect realized promiscuity of females. Third, EPF decisions depend on the combined effects of the identity of social mates. Here, we relied on extensive genetic parentage analysis of the offspring of a socially monogamous bird, the barn swallow, Hirundo rustica, to assess which of the above sources of variation predict the occurrence of EPFs. When we controlled for pair composition and social mate attractiveness, EPFs covaried with morphological and coloration traits of feathers in females. As expected, females mated with highly ornamented, long-tailed males had fewer EPFs. The composition of the breeding pair also accounted for variation in EPFs, implying that the ability of individual males to secure genetic parentage varies between female mates. These results show that females differ in promiscuity, and phenotypic traits of females that are visible to males are associated with promiscuity, potentially serving as cues to prospecting males. Hence, contrary to common interpretations of the negative relationship between male sexual attractiveness and female promiscuity, it can be speculated that larger genetic parentage by highly ornamented males results from their ability to secure the less promiscuous mates rather than from females being less promiscuous when mated to them. Moreover, our study shows that EPFs also depend on the composition of the social pair, as expected if a component of female promiscuity decisions depends on genetic or behavioural compatibility with the social male mate. Our study emphasizes that female promiscuity and its phenotypic correlates, and composition of the social pair, deserve closer attention in studies of sexual selection medi

Life of many organisms flows as a sequence of annual cycles. Timing of cyclical events is shaped by natural selection also via the domino effects that any life history stage has on the stages that follow. Such ‘carry-over effects’ have major consequences for evolutionary, ecological and demographic processes, but the causes that generate their individual-level variation, including the effect of sex, are poorly understood. We used light-level geolocators to study carry-over effects on the year-round life cycle of the long-distance migratory barn swallow (Hirundo rustica) and sex-dependent variation in their strength. Correlation analyses showed that timing of breeding influenced departure time for autumn migration in females but not in males. In addition, strong, time-mediated carry-over effects of timing of departure from the wintering areas in sub-Saharan Africa for spring migration on timing of arrival to the breeding grounds in Italy and Switzerland operated in both sexes. However, carry-over effects of spring migration phenology on breeding date and seasonal fecundity were observed among females but not among males. We used partial least squares path modelling to unveil the complex carry-over effects of phenology during the non-breeding season in combination with the ecological conditions experienced by individual swallows in the wintering area, as gauged by Normalized Difference Vegetation Index values (NDVI), on breeding performance. Phenology during the non-breeding season combined with NDVI during wintering accounted for as much as 65–70% of variation in subsequent seasonal fecundity in females, while such carry-over effects on breeding success of males were weaker. Intense, sex-specific carry-over effects can have impacted on evolutionary processes, including sexual selection, and affected phenological response to climate change, causing the large population decline observed in this species

Capsule: Growth trajectories of Blue Tit Cyanistes caeruleus nestlings differed between sexes and were negatively affected by rain but not by temperature during the linear growth phase (LGP). Aims: To model the growth trajectories of Blue Tit nestlings and to identify the main ecological factors affecting them. Methods: Sixty-five nestling Blue Tits from a population in northern Italy were weighed at regular intervals and sexed using molecular genetic techniques. The LGP period was identified and analysed to test for the influence of age, sex, hatching date, brood size, temperature and rainfall on individual daily growth rates during the LGP. Results: Growth curves showed no pre-fledging mass loss. Body mass differed between the sexes, with males being 5% heavier than females at the pre-fledging stage. Daily growth rates during the LGP were higher for males and on non-rainy days, while they were not affected by other factors. Conclusion: The higher daily growth rate observed in males during the LGP may determine the extent of sexual size dimorphism at the pre-fledging stage. Susceptibility of growth trajectories to environmental conditions was limited to rainfall and was similar in the two sexes. This contrasts with findings from previous studies, which found sex-biased environmental sensitivity of Blue Tit nestlings

Wings have evolved in phylogenetically distant organisms with morphologies that depend on the combined effects of diverse, potentially contrasting selective forces. In birds, long pointed wings boost speed and energetic efficiency during cruising flight but reduce manoeuvrability. Migratory behavior is believed to lead to the evolution of more pointed wings, but selection on pointedness has never been estimated. Because annual routines of migrants are tightly scheduled, wing pointedness may be selected for because it allows for earlier arrival to the breeding grounds. In long-distance migratory barn swallows Hirundo rustica we showed that selection via breeding date and thus annual fecundity operates on wing pointedness, but not on other wing traits, among yearling females but not among older females or males. Selection on wing pointedness specifically in yearling females may result from climatic effects, which favour earlier arrival from migration, and from yearling females being the sex-by-age class with the latest migration and the smallest wing pointedness. Wing morphology differed between sexes and age classes because of change in size of the outermost but not the innermost wing feathers. Hence, sex- and age-specific selection on wing pointedness operates in a species with sex- and age-dependent variation in phenology and wing morphology

The consequences of exposure to particulate matter (PM) have been thoroughly investigated in humans and other model species, but there is a dearth of studies of the effects of PM on physiology and life-history traits of non-human organisms living in natural or semi-natural environments. Besides toxicological relevance, PM has been recently suggested to exert epigenetic effects by altering DNA methylation patterns. Here, we investigated for the first time the association between the exposure to free-air PM10 and DNA methylation at two loci (‘poly-Q exon’ and ‘5′-UTR’) of the Clock gene in blood cells of the nestlings of a synanthropic passerine bird, the barn swallow (Hirundo rustica). The Clock gene is a phylogenetically highly conserved gene playing a major role in governing circadian rhythms and circannual life cycles of animals, implying that change in its level of methylation can impact on important fitness traits. We found that methylation at both loci significantly increased with PM10 levels recorded few days before blood sampling, and also with PM10 exposure experienced by the mother during or shortly before egg laying. This study is the first where methylation at a functionally important gene has been shown to vary according to the concentration of anthropogenic pollutants in any animal species in the wild. Since early-life environmental conditions produce epigenetic effects that can transgenerationally be transmitted, DNA methylation of genes controlling photoperiodic response can have far reaching consequences for the ecology and the evolution of wild animal populations.

Migratory behaviour is controlled by endogenous circannual rhythms that are synchronized by external cues, such as photoperiod. Investigations on the genetic basis of circannual rhythmicity in vertebrates have highlighted that variation at candidate ‘circadian clock’ genes may play a major role in regulating photoperiodic responses and timing of life cycle events, such as reproduction and migration. In this comparative study of 23 trans-Saharan migratory bird species, we investigated the relationships between species-level genetic variation at two candidate genes, Clock and Adcyap1, and species’ traits related to migration and geographic distribution, including timing of spring migration across the Mediterranean Sea, migration distance and breeding latitude. Consistently with previous evidence showing latitudinal clines in ‘circadian clock’ genotype frequencies, Clock allele size increased with breeding latitude across species. However, early- and late-migrating species had similar Clock allele size. Species migrating over longer distances, showing delayed spring migration and smaller phenotypic variance in spring migration timing, had significantly reduced Clock (but not Adcyap1) gene diversity. Phylogenetic confirmatory path analysis suggested that migration date and distance were the most important variables directly affecting Clock gene diversity. Hence, our study supports the hypothesis that Clock allele size increases poleward as a consequence of adaptation to the photoperiodic regime of the breeding areas. Moreover, we show that long-distance migration is associated with lower Clock diversity, coherently with strong stabilizing selection acting on timing of life cycle events in long-distance migratory species, likely resulting from the time constraints imposed by late spring migration.

Many partially migratory species show phenotypically divergent populations in terms of migratory behaviour, with climate hypothesized to be a major driver of such variability through its differential effects on sedentary and migratory individuals. Based on long-term (1947-2011) bird ringing data, we analysed phenotypic differentiation of migratory behaviour among populations of the European robin Erithacus rubecula across Europe. We showed that clusters of populations sharing breeding and wintering ranges varied from partial (British Isles and Western Europe, NW cluster) to completely migratory (Scandinavia and north-eastern Europe, NE cluster). Distance migrated by birds of the NE (but not of the NW) cluster decreased through time because of a north-eastwards shift in the wintering grounds. Moreover, when winter temperatures in the breeding areas were cold, individuals from the NE cluster also migrated longer distances, while those of the NW cluster moved over shorter distances. Climatic conditions may therefore affect migratory behaviour of robins, although large geographical variation in response to climate seems to exist.

Sex allocation theory predicts that parents are selected to bias their progeny sex ratio (SR) toward the sex that will benefit the most from parental quality. Because parental quality may differentially affect survival of sons and daughters, a pivotal test of the adaptive value of SR adjustment is whether parents overproduce offspring of the sex that accrues larger fitness advantages from high parental quality. However, this crucial test of the long-term fitness consequences of sex allocation decisions has seldom been performed. In this study of the barn swallow (Hirundo rustica), we showed a positive correlation between the proportion of sons and maternal annual survival. We then experimentally demonstrated that this association did not depend on the differential costs of rearing offspring of either sex. Finally, we showed that maternal lifespan positively predicted lifespan of sons but not of daughters. Because in barn swallows lifespan is a strong determinant of lifetime reproductive success, the results suggest that mothers overproduce offspring of the sex that benefits the most from maternal quality. Hence, irrespective of mechanisms causing the SR bias and mother-son covariation in lifespan, we provide strong evidence that sex allocation decisions of mothers can highly impact on their lifetime fitness.

Several populations of long-distance migratory birds are currently suffering steep demographic declines. The identification of the causes of such declines is difficult because population changes may be driven by events occurring in distant geographical areas during different phases of the annual life-cycle of migrants. Furthermore, wintering areas and migration routes of populations of small-sized species are still largely unknown, with few exceptions. In this paper we identified the critical phases of the annual life-cycle that most influence the population dynamics of a small passerine, the Barn Swallow Hirundo rustica. We used information on temporal dynamics of a population breeding in Northern Italy, whose wintering range and timing of migration have been recently described by miniaturised tracking dataloggers. Our results indicated that primary productivity in the wintering grounds in the month when most individuals arrive from autumn migration and primary productivity in an area that is probably a stopover site during spring migration, influenced population dynamics more than habitat conditions at the breeding grounds. By using annual variation in primary productivity at the wintering grounds and stopover sites as predictors, we replicated the observed interannual population changes with great accuracy. However, the steep decline recently suffered by the population could be replicated only by including a constant annual decline in the model, suggesting that changes in primary productivity only predicted the interannual variation around the long-term trend. Our study therefore suggests the existence of critical periods during wintering and migration that may have large impact on population fluctuations of migrant birds.

Despite benefits of using light-sensitive geolocators to track animal movements and describe patterns of migratory connectivity, concerns have been raised about negative effects of these devices, particularly in small species of aerial insectivore.Geolocators may act as handicaps that increase energetic expenditure, which could explain reported effects of geolocators on survival.We tested this ‘Energetic Expenditure Hypothesis’ in 12 populations of tree swallows (Tachycineta bicolor) and barn swallows (Hirundo rustica) from North America and Europe, usingmeasurements of corticosterone from feathers (CORTf) grown after deployment of geolocators as a measure of physiology relevant to energetics. Contrary to predictions, neither among- (both species) nor within-individual (tree swallows only) levels of CORTf differed with respect to instrumentation. Thus, to the extent that CORTf reflects energetic expenditure, geolocators apparently were not a strong handicap for birds that returned post-deployment. While this physiological evidence suggests that information about migration obtained from returning geolocator-equipped swallows is unbiased with regard to levels of stress, we cannot discount the possibility that corticosterone played a role in reported effects of geolocators on survival in birds, and suggest that future studies relate corticosterone to antecedent factors, such as reproductive history, and to downstream fitness costs.

The determinants and function of pigmentation of feathers and other tissues have been the focus of a large number of studies, particularly with respect to socio-sexual communication. However, many birds exhibit depigmented white spots or bars on their feathers whose function is poorly understood. Here we assess whether white feather spots reflect phenotypic condition at the time of moult by investigating the covariation between spot size or shape and condition-dependent feather growth rate, as gauged by width of the growth bars on the tail feathers of Barn Swallows. We found that feathers with higher growth rates had larger, less rounded white spots. In addition, variance in spot perimeter for a given spot area was larger in males than in females. This study is the first to provide evidence that features of white markings on feathers directly reflect body condition at the time of moult and can therefore reliably signal phenotypic quality in the context of socio-sexual communication. In addition, the study highlights the potential communication function of the shape and not just the size of colour signals.

Contingent individual performance can depend on the environment experienced at previous life-stages. Migratory birds are especially susceptible to such carry-over effects as they periodically travel between breeding ranges and ‘wintering’ areas where they may experience broadly different ecological conditions. However, the study of carry-over effects is hampered by the difficulty of tracking vagile organisms throughout their annual life-cycle. Using information from light-level geolocators on the barn swallow (Hirundo rustica), we tested if feather growth bar width (GBW), a proxy of feather growth rate which depends on individual condition, and wing isometric size and shape predict the phenology of subsequent migration. GBW did not predict duration of wintering but negatively predicted the duration of spring migration and arrival date to the breeding sites, suggesting that migration phenology is not constrained by molt, and individuals in prime condition achieve both faster molt and earlier arrival. Wing morphology did not predict migration duration, as expected if wing shape were optimized for foraging, rather than migration performance, in this aerially foraging, insectivorous bird. Thus, we showed for the first time that migration phenology in a long-distance migratory bird covaries with body condition during wintering, as reflected by the growth rate of feathers.

Dissecting phenotypic variance in life history traits into its genetic and environmental components is at the focus of evolutionary studies and of pivotal importance to identify the mechanisms and predict the consequences of human-driven environmental change. The timing of recurrent life history events (phenology) is under strong selection, but the study of the genes that control potential environmental canalization in phenological traits is at its infancy. Candidate genes for circadian behaviour entrained by photoperiod have been screened as potential controllers of phenological variation of breeding and moult in birds, with inconsistent results. Despite photoperiodic control of migration is well established, no study has reported on migration phenology in relation to polymorphism at candidate genes in birds. We analysed variation in spring migration dates within four trans-Saharan migratory species (Luscinia megarhynchos; Ficedula hypoleuca; Anthus trivialis; Saxicola rubetra) at a Mediterranean island in relation to Clock and Adcyap1 polymorphism. Individuals with larger number of glutamine residues in the poly-Q region of Clock gene migrated significantly later in one or, respectively, two species depending on sex and whether the within-individual mean length or the length of the longer Clock allele was considered. The results hinted at dominance of the longer Clock allele. No significant evidence for migration date to covary with Adcyap1 polymorphism emerged. This is the first evidence that migration phenology is associated with Clock in birds. This finding is important for evolutionary studies of migration and sheds light on the mechanisms that drive bird phenological changes and population trends in response to climate change.

Altricial offspring solicit parental care using complex begging displays. Although such solicitations are mainly performed towards parents, nestlings of several birds often beg when parents are not at the nest. This parent-absent begging (PAB) has been interpreted as a mistake in correctly detecting parental arrival, but it may also reliably signal individual need to nest mates, potentially affecting intra-brood competition for food. Here, we focused on the proximate factors that may determine frequency and intensity of PAB, including brood size and sex ratio, as well as individual age, sex and body mass, in natural barn swallow (Hirundo rustica) broods, under conditions of normal and experimentally reduced food intake. We also investigated the relationship between PAB and begging intensity at parental arrival and food intake in the two different experimental conditions. The frequency of PAB was larger after food deprivation than before, indicating that PAB reliably reflects hunger level. In addition, nestlings increased their own begging intensity upon parental arrival after performing PAB. Concomitantly, siblings decreased begging effort, irrespective of sex or body mass, but this occurred only when nestlings were normally fed, suggesting that PAB diminishes scrambling for food by nest mates. Finally, such a reciprocal begging modulation resulted in a larger chance of obtaining food at the subsequent feeding event for nestlings performing PAB under normal food provisioning. Within-brood signalling in the absence of parents can therefore play an important role in determining competitive strategies among siblings and affecting parental decisions on food allocation in altricial broods.

We investigated sex- and year-dependent variation in the temporal and spatial movement pattern of barn swallows Hirundo rustica during the non-breeding period. Hundred and three individuals equipped with miniaturized light-level geolocators at three different breeding areas in southern Switzerland and northern Italy provided data for the analysis. We identified a region 1000 km in radius centred in Cameroon as the main non-breeding residence area of these three geographical populations. Five residence areas of males only were in southern Africa, south of 19°S. Most individuals occupied a single site during their stay south of the Sahara. The timing of migration broadly overlapped between sexes and all geographical breeding populations. Between the two study years there was a distinct difference of 5 to 10 d in departure dates from and arrival at the breeding sites. Remarkably, the period of residence in sub-Saharan Africa was very similar (157 d) in the two study years, but their positions in the first year (2010-2011) were about 400 km more to the north than in the second (2011-2012). Independent of the year, individuals with sub-Saharan residence areas further north and east had a shorter pre-breeding migration and arrived earlier than those staying further south and west. In addition, birds breeding in southern Switzerland arrived at their breeding colony 7-10 d later than those breeding only 100 km south, in the Po river plain. Our study provides new information on the variance in migration phenology and the distribution of residence areas in sub-Saharan Africa in relation to sex, population and year. It supports the usefulness of light-level geolocators for the study of annual routines of large samples of small birds.

Capsule Hatching order negatively affected Common Swift Apus apus nestlings survival, while brood size and meteorological conditions influenced their growth patterns. Aims To investigate the influence of hatching date, age, sex, brood size and meteorological conditions on survival and growth of Common Swift nestlings from Northern Italy (Southern Europe), a relatively warm and dry part of the distribution range of this species. Methods Nestlings were weighed at regular intervals and molecularly sexed. Growth patterns were described using a double-Richards growth curve, i.e. a growth curve that also accounted for the pre-fledging mass loss. We also identified the Linear Growth Phase (i.e. when nestlings grew at the fastest rate). Results Mortality increased with hatching order and decreased with brood size. Mortality was highest for fourth-hatched nestlings, none of which survived. Nestlings hatched late in the season grew faster, experienced the fastest growth rate at a younger age, but reached a lower maximum weight than nestlings hatched early in the season. Nestlings from large broods reached a lower maximum weight than those of small ones. Nestlings gained more mass when temperature was slightly higher than that expected from the seasonal temperature trend, and on rainy and windy days. Conclusion Common Swift nestlings growth, but not survival, was affected by meteorological conditions, with moderate rainfall, moderate winds and high temperatures favouring greater mass gain. Higher intra-brood competition resulted in slower growth and lower maximum weight. Late-hatched nestlings grew faster but reached a lower maximum weight and a lower pre-fledging mass, possibly suggesting that late-hatched nestlings adaptively tune their growth pattern to the approaching onset of migration to their African wintering quarters. Our results emphasize the importance of exploring weather effects on the breeding biology of a species in different portions of its distribution range t

Reproduction is a demanding activity, since organisms must produce and, in some cases, protect and provision their progeny. Hence, a central tenet of life-history theory predicts that parents have to trade parental care against body maintenance. One physiological cost thought to be particularly important as a modulator of such trade-offs is oxidative stress. However, evidence in favour of the hypothesis of an oxidative cost of reproduction is contradictory. In this study, we manipulated the brood size of wild barn swallows Hirundo rustica soon after hatching of their nestlings to test whether an increase in nestling rearing effort translates into an increased oxidative damage and a decreased antioxidant protection at the end of the nestling rearing period. We found that, while plasma oxidative damage was unaffected by brood size enlargement, females rearing enlarged broods showed a decrease in plasma non-enzymatic antioxidants during the nestling rearing period. This was not the case among females rearing reduced broods and among males assigned to either treatment. Moreover, individuals with higher plasma oxidative damage soon after the brood size manipulation had lower plasma non-enzymatic antioxidants at the end of the nestling rearing period, suggesting that non-enzymatic antioxidants were depleted to buffer the negative effects of high oxidative damage. Our findings point to antioxidant depletion as a potential mechanism mediating the cost of reproduction among female birds. © 2014 Springer-Verlag Berlin Heidelberg

Moonlight is known to affect the nocturnal behaviour and activity rhythms of many organisms. For instance, predators active at night may take advantage from increased visibility afforded by the moon, while prey might regulate their activity patterns to become less detectable. Many spe- cies of pelagic seabirds attend their colony only at night, in complete dark- ness, avoiding approaching their nest sites under moonlight. This behaviour has been most often interpreted as an antipredator adaptation (‘predation avoidance’ hypothesis). However, it may also reflect a lower foraging efficiency during moonlit nights (‘foraging efficiency’ hypothe- sis). Indeed, moonlight may reduce prey availability because preferred seabird prey is known to occur at higher depths in moonlit nights. Using high-accuracy behavioural information from data loggers, we investigated the effect of moonlight on colony attendance and at-sea nocturnal forag- ing in breeding Scopoli’s shearwaters Calonectris diomedea. We found that birds departing for self-feeding trips around the full moon performed longer trips than those departing around the new moon. On nights when the moon was present only partly, nest burrow entrances took place lar- gely in the moonless portion of the night. Moreover, contrary to predic- tions from the ‘foraging efficiency’ hypothesis, nocturnal foraging activity increased according to moonlight intensity, suggesting that birds increased their foraging activity when prey became more detectable. This study strengthens the idea that colony attendance behaviour is strictly con- trolled by moonlight in shearwaters, which is possibly related to the per- ception of a predation risk.

Physiological trade-offs mediated by limiting energy, resources or time constrain the simultaneous expression of major functions and can lead to the evolution of temporal separation between demanding activities. In birds, plumage renewal is a demanding activity, which accomplishes fundamental functions, such as allowing thermal insulation, aerodynamics and socio-sexual signaling. Feather renewal is a very expensive and disabling process, and molt is often partitioned from breeding and migration. However, trade-offs between feather renewal and breeding have been only sparsely studied. In barn swallows (Hirundo rustica) breeding in Italy and undergoing molt during wintering in sub-Saharan Africa, we studied this trade-off by removing a tail feather from a large sample of individuals and analyzing growth bar width, reflecting feather growth rate, and length of the growing replacement feather in relation to the stage in the breeding cycle at removal and clutch size. Growth bar width of females and length of the growing replacement feather of both sexes were smaller when the original feather had been removed after clutch initiation. Importantly, in females both growth bar width and replacement feather length were negatively predicted by clutch size, and more strongly so for large clutches and when feather removal occurred immediately after clutch completion. Hence, we found strong, coherent evidence for a trade-off between reproduction, and laying effort in particular, and the ability to generate new feathers. These results support the hypothesis that the derived condition of molting during wintering in long-distance migrants is maintained by the costs of overlapping breeding and molt. © 2014 Saino et al.

Migration is a fundamental stage in the life history of several taxa, including birds, and is under strong selective pressure. At present, the only data that may allow for both an assessment of patterns of bird migration and for retrospective analyses of changes in migration timing are the databases of ring recoveries. We used ring recoveries of the Barn Swallow Hirundo rustica collected from 1908–2008 in Europe to model the calendar date at which a given proportion of birds is expected to have reached a given geographical area (‘progression of migration’) and to investigate the change in timing of migration over the same areas between three time periods (1908–1969, 1970–1990, 1991–2008). The analyses were conducted using binomial conditional autoregressive (CAR) mixed models. We first concentrated on data from the British Isles and then expanded the models to western Europe and north Africa. We produced maps of the progression of migration that disclosed local patterns of migration consistent with those obtained from the analyses of the movements of ringed individuals. Timing of migration estimated from our model is consistent with data on migration phenology of the Barn Swallow available in the literature, but in some cases it is later than that estimated by data collected at ringing stations, which, however, may not be representative of migration phenology over large geographical areas. The comparison of median migration date estimated over the same geographical area among time periods showed no significant advancement of spring migration over the whole of Europe, but a significant advancement of autumn migration in southern Europe. Our modelling approach can be generalized to any records of ringing date and locality of individuals including those which have not been recovered subsequently, as well as to geo-referenced databases of sightings of migratory individuals

Prenatal and early postnatal conditions can prime developmental trajectories, with short- as well as major long-term effects on phenotype. Variance in perinatal conditions may be caused by many factors, including number of siblings of either sex, which is expected to influence individual phenotype for two complementary reasons. First, male and female offspring can differ in susceptibility to extrinsic conditions. Second, the effect that an individual has on its siblings can differ according to their sex. Yet, few studies of vertebrates and only one of birds have addressed the long-term consequences of family sex composition on offspring of either sex. We analysed the effect of brood sex composition on adult phenotype and breeding performance in the barn swallow, Hirundo rustica. Male offspring growing with more sisters had shorter wing length, an aerodynamically important trait, and tail length, a conditiondependent, sexually selected trait. In addition, tail length of females decreased with increasing brood size but more steeply so when they grew with more female siblings. Body size of females also declined with increasing brood size. Notably, breeding output of females declined with an increasing proportion of male siblings and also with increasing brood size. This study thus suggests that social environment has major consequences for phenotype and breeding performance in adulthood and that variation in brood sex composition has long-term effects which depend on the sex of the individual as well as on the specific trait considered. Hence, optimal parental sex allocation decisions depend not simply on additive fitness costs and benefits of producing males or females, but also on the long-term effects that sons and daughters exert on each other

Miniaturized light-level geolocators may revolutionise the study of avian migration. However, there are increasing concerns that they might negatively affect fitness. We investigated the impact of two miniaturized geolocator models (SOI-GDL2.10, deployed in 2010, and SOI-GDL2.11, deployed in 2011) on fitness traits of the barn swallow Hirundo rustica, one of the smallest migratory species to which geolocators have been applied to date. The 2011 model was lighter (by 0.09 g) and had a shorter light stalk compared to the 2010 model. Using data from 640 geolocator and 399 control individuals from three geographical populations, we found that geolocators reduced annual survival probabilities (control birds: 0.19–0.63; geolocator birds: 0.08–0.40, depending on year, sex, and how birds that lost the device were considered), with more markedly negative effects on females equipped with the 2010 model. In addition, among birds equipped with the 2010 model, onset of reproduction in the subsequent year was delayed (by 12 d) and females laid smaller first clutches (by 1.5 eggs, i.e. a 30% reduction) compared to controls. Equipping parents with geolocators while they were attending their brood did not affect nestling body mass or fledging success. A reduction of geolocator weight and drag by shortening the light stalk slightly enhanced the survival of females but not that of males, and mitigated the negative carry-over effects on subsequent reproduction. Our study shows that geolocators can have a negative impact on survival and reproduction, and that even minor differences in weight and drag can make the difference. We suggest that studies aiming at deploying geolocators or other year-round tagging devices should be preceded by pilot experiments to test for fitness effects.

Natal dispersal is a major life-history trait, with important consequences for population dynamics and genetic structure. Successful dispersal depends on a complex blend of decisions at all main stages of the dispersal process: emigration, prospection for a site, and settling. Costs and benefits of such decisions are expected to depend on sex and on the ecological context, on individual physiological state, and on concomitant decisions by relatives, which affect competition with kin and inbreeding. We analyzed natal dispersal propensity (i.e., dispersing or not) and dispersal distance in the semicolonial barn swallow (Hirundo rustica) in relation to context-, phenotype-, and kin-dependent factors. Females had larger dispersal propensity and distance than males. Dispersal propensity of both sexes was negatively density dependent and was less likely from colonies (farms) with large number of livestock, which is important to barn swallow distribution. Dispersal propensity was larger among males ranking high in the body mass brood hierarchy and smaller among late-hatched females. Dispersal distance was larger for late-hatched males and for females that ranked high in the body mass brood hierarchy. Finally, both dispersal propensity and distance of males increased with the number of male siblings. We, thus, identified several context-, phenotype-, and kin-dependent components of dispersal decisions. Phenotype-dependent effects suggest that decisions of whether to disperse and of dispersal distance are different processes under control of sex-specific traits. Finally, male dispersal behavior suggests that kin selection favors males that reduce the risk of sib–sib mating competition, in a population with male-biased tertiary sex ratio.

Natal dispersal contributes to population dynamics and genetic structure. Individuals differ in whether or not they disperse and in the distance they travel from their natal site before settling to breed. Differences in natal dispersal are often associated with variation in other traits. These associations may arise because suites of morphological and behavioural traits are ultimately controlled by the same set of genes. The genes that control melanogenesis in vertebrates pleiotropically influence physiology and behaviour, including boldness and exploration. Because these personality traits predict dispersal, we tested the hypothesis that in the barn swallow, Hirundo rustica, melanic coloration predicts natal dispersal, using a solid matched caseecontrol sampling design and a large sample. We found that males but not females with colour traits that reflect relatively more pheomelanic feather pigmentation were more likely to disperse, consistently with observations on the only other species for which dispersal in relation to plumage melanic coloration has so far been studied. To control for any confounding effects, we also analysed the association of dispersal with morphological traits and parasite infestation. Philopatric individuals were larger than dispersers, whereas dispersal strategy did not differ according to tail length, which is a sexually selected trait. Finally, philopatric females had a smaller infestation of a haematophagous louse fly. The present findings corroborate previous evidence that melanic coloration covaries with a suite of traits. In particular, they show that melanin-based plumage coloration predicts natal dispersal, independently of other factors also influencing dispersal. In addition, our results show that philopatric individuals were larger than dispersers possibly because individuals return to a benign natal place or because large body size confers an advantage in competitive interactions. Finally, they are compatible with the idea of h

The widespread decline of farmland birds is a major issue of biological conservation in European countries. The Barn Swallow Hirundo rustica is a flagship species for farmland bird conservation owing to its aesthetic and cultural value and to the sharp decline observed in several populations. Based on a long-term monitoring project of a population in a protected area of Northern Italy, we documented a dramatic decline of 56.6% between 1999 and 2011, corresponding to a decrease of 6.59% each year. We also showed that colonies were on average larger in farms with livestock than those without livestock, and that colony size increased with increasing extent of hayfields within 200 m from the colony in farms without livestock, but not in those with livestock. Hayfield extent at greater distances did not influence population size or trend. Cessation of livestock farming therefore determined a decline in local colonies, but this decline may be buffered by an increase in hayfield extent within 200 m from the farm. However, variation in the ecological features of breeding sites explained only a fraction of the observed population decline, suggesting that ecological conditions during migration and wintering may be crucial in affecting population trends. Mean hatching date of first broods advanced in recent years, but less so in farms with, than without, livestock. Independently of year, mean hatching date advanced more in farms with greater extent of hayfields within 200 m of the colony. Reproductive success, measured as the mean number of fledged offspring per nest, declined significantly with hatching date, but was not affected by hayfield extent. Conversely, nestling quality, in terms of body mass and feather development, improved with increasing extent of hayfields around the colony, particularly in late-hatched first clutches. Our findings suggest that conservation strategies for this declining species should include both the maintenance of livestock farming and the enla

Melanin is the main pigment in animal coloration and considerable variation in the concentrations of the two melanin forms (pheo- and eumlanin) in pigmented tissues exists among populations and individuals. Melanin-based coloration is receiving increasing attention particularly in socio-sexual communication contexts because the melanocortin system has been hypothesized to provide a mechanistic basis for covariation between coloration and fitness traits. However, with few notable exceptions, little detailed information is available on inter-individual and inter-population variation in melanin pigmentation and on its environmental, genetic and ontogenetic components. Here, we investigate melanin-based coloration in an Italian population of a passerine bird, the barn swallow (Hirundo rustica rustica), its sex- and age-related variation, and heritability. The concentrations of eu- and pheomelanin in the throat (brown) and belly (white-to-brownish) feathers differed between sexes but not according to age. The relative concentration of either melanin (Pheo:Eu) differed between sexes in throat but not in belly feathers, and the concentrations in males compared to females were larger in belly than in throat feathers. There were weak correlations between the concentrations of melanins within as well as among plumage regions. Coloration of belly feathers was predicted by the concentration of both melanins whereas coloration of throat feathers was only predicted by pheomelanin in females. In addition, Pheo:Eu predicted coloration of throat feathers in females and that of belly feathers in males. Finally, we found high heritability of color of throat feathers. Melanization was found to differ from that recorded in Hirundo rustica rustica from Scotland or from H. r. erythrogaster from North America. Hence, present results show that pigmentation strategies vary in a complex manner according to sex and plumage region, and also among geographical populations, potentially reflecting

Early life conditions may have important long-term consequences on viability and reproduction. Considering their pervasiveness in natural environments, parasites play a crucial role in determining life-histories of hosts, by negatively affecting their performance and imposing fitness costs. Here, we tested whether exposure to a bacterial endotoxin (lipopolysaccharide, LPS) during the nestling period influenced breeding performance at sexual maturation of a small passerine bird, the barn swallow (Hirundo rustica). Three out of 56 LPS male nestlings were recruited in their breeding site, compared to six out of 51 controls. None of the LPS recruits was observed to breed or to pair with a female, while all control recruits bred successfully, with a mean seasonal breeding success of 6.4 fledged offspring. In addition, LPS recruits were captured later than controls. Despite the low sample size, our results suggest that exposure to a bacterial endotoxin during the critical phase of development may negatively affect reproductive success in these short-lived migratory birds, possibly via delaying timing of moult and arrival from wintering grounds.

Sex ratio of adults (tertiary sex ratio, TSR) is a major feature of animal populations with consequences for their behaviour, genetic structure and viability. Spatial and temporal variation in TSR occurs within species but the mechanisms behind it are poorly understood. In this long-term study of a declining population of a socially monogamous, colonial, migratory bird, the barn swallow (Hirundo rustica), we first analyzed population-level variation in TSR ( = proportion of males) of yearlings at sexual maturation in relation to ecological conditions as gauged by annual survival rate of adults. TSR was male-biased both among yearlings and older individuals, but male bias of yearlings was more pronounced after years with larger decline in adult survival. Thus, male offspring were less susceptible to the adverse ecological conditions that cause increased mortality. Dispersal and settling site decisions can have major consequences on fitness via the effects of local TSR on mating and sperm competition. Breeding barn swallows are highly philopatric while natal dispersal is high and, together with mortality, is the main determinant of colony TSR. We thus also investigated the mechanisms of breeding colony choice by yearlings and found that TSR of new-settlers in a given colony and year was negatively predicted by TSR of returning, early arriving older individuals in that year, but not by overall TSR at the colony in the previous year. This suggests that in our male-biased population new-settler males respond to local TSR upon arrival to choose the sites with larger breeding opportunities. Hence, variation in ecological conditions as reflected by adult survival can shift the TSR of individuals recruiting into a local population, with potentially various demographic consequences. However, breeding site choice based on TSR tends to homogenize TSR at a population level likely by facilitating settling of dispersing males in colonies with less male-biased TSR.

Studies of avian species have shown that maternal effects mediated by the transfer of egg hormones can profoundly affect offspring phenotype and fitness. We previously demonstrated that the injection of a physiological amount of testosterone (T) in the eggs of ring-necked pheasants (Phasianus colchicus) disrupted the covariation among male morphological traits at sexual maturity and positively affected male mating success. Here, we investigate whether egg T exposure affected adult male circulating T levels at the onset of the breeding season (reflecting gonadal maturation), and the relationship between circulating T and male traits. Egg T exposure did not affect pre-mating plasma T. T levels were not associated with the expression of secondary sexual and non-sexual traits or socio-sexual behaviour (social rank, overall fighting ability and mating success). However, wattle brightness decreased with increasing circulating T in males hatched from T-eggs (T-males) but not among control males. In dyadic encounters during the peak mating period, control males with higher premating T levels had higher chances of being dominant over other control males. However, higher pre-mating T levels did not predict success in male-male competition in encounters involving T-males. We suggest that the long-term effects of egg T on male phenotype do not originate from differential gonadal maturation according to egg T treatment. Rather, prenatal androgens may have priming effects on functioning of target tissues, translating into differential phenotypic effects according to androgen exposure during embryonic development