Translocation of shorebird siblings shows intraspecific variation in migration routines to arise after fledging

Although many recent tracking studies have uncovered considerable variation in the migratory routines of birds,1,2 the source of this variation is surprisingly poorly discussed.3 We hypothesize that a wealth of possible factors, including factors other than genetics, translate into these variable outcomes. To demonstrate how factors that are not inherited can shape migratory routine during development, we performed a translocation and delayed-release experiment with juvenile, hand-raised black-tailed godwits Limosa limosa limosa that were carefully matched for ancestral background, releasing siblings 1,000 km apart. Translocated juveniles adopted the spatiotemporal pattern of migration that is habitual for the population at the release location rather than the origin. This leads to the rejection of the hypothesis that the migration of inexperienced birds is only shaped by pre-release factors, including genes, maternal material in the eggs, and a common environment from hatching to fledging. Instead, these findings are consistent with inexperienced migrants also developing their knowledge and capacities through contextual individual learning,4 the precise nature of which now warrants study. The fact that hand-raised godwits, depending on the context in which they are released, can be induced to show different migratory routines, wintering sites, and breeding locations from their siblings indicates that processes during development offer the substrate for rapid adaptation of long-distance migration

Quantifying the non-breeding provenance of staging Ruffs, <i>Philomachus pugnax</i>, using stable isotope analysis of different tissues

International conservation efforts for migratory populations are most effectively based on quantification of the geographical linkages between wintering, staging, and breeding areas, patterns that may not remain constant in times of global change. We used stable isotope (δ 13C, δ 15N, and δ 2H) measurements of different tissues representing distinct periods of dietary integration to quantify the non-breeding provenance of a threatened staging population of Ruffs Philomachus pugnax. In 199 staging Ruffs captured in 2012 during northward migration in the Netherlands, we compared the multi-isotope patterns of feathers grown at wintering grounds, with the δ 13C and δ 15N profiles of blood cells and plasma representative of staging areas. Few birds had the 13C-depleted and 15N-enriched feathers suggestive of wintering quarters in European agricultural areas. Most Ruffs had higher feather δ 13C values, suggesting that they wintered in sub-Saharan Africa. Feather δ 2H values were not informative due to the overlap of values from European and African moulting sites. Blood cell δ 13C and δ 15N values indicated that sub-Saharan Ruffs fuelled on low trophic-level foods in habitats dominated by C3 terrestrial or freshwater aquatic primary production, e.g. the rice fields in Africa or the Mediterranean. Stable isotope ratios in plasma suggested that Ruffs made stopovers in southern European agricultural areas. Stable isotopes thus enabled assessments of wintering origin in large numbers of birds. We further propose that conservation measures to protect Ruffs must include the adequate management of sub-Saharan wetlands, based on a better understanding of the role of human-made rice fields for fuelling birds

Influence of age and sex on winter site fidelity of sanderlings Calidris alba

Many migratory bird species show high levels of site fidelity to their wintering sites, which confers advantages due to prior knowledge, but may also limit the ability of the individual to move away from degrading sites or to detect alternative foraging opportunities. Winter site fidelity often varies among age groups, but sexual differences have seldom been recorded in birds. We studied a population of individually colour-marked sanderlings wintering in and around the Tejo estuary, a large estuarine wetland on the western coast of Portugal. For 160 individuals, sighted a total of 1,249 times between November 2009 and March 2013, we calculated the probability that they moved among five distinct wintering sites and how this probability is affected by distance between them. To compare site fidelity among age classes and sexes, as well as within the same winter and over multiple winters, we used a Site Fidelity Index (SFI). Birds were sexed using a discriminant function based on biometrics of a large set of molecularly sexed sanderlings (n = 990). The vast majority of birds were observed at one site only, and the probability of the few detected movements between sites was negatively correlated with the distance among each pair of sites. Hardly any movements were recorded over more than 15 km, suggesting small home ranges. SFI values indicated that juveniles were less site-faithful than adults which may reflect the accumulated knowledge and/or dominance of older animals. Among adults, females were significantly less site faithful than males. A sexual difference in winter site fidelity is unusual in shorebirds. SFI values show site-faithfulness is lower when multiple winters were considered, and most birds seem to chose a wintering site early in the season and use that site throughout the winter. Sanderlings show a very limited tendency to explore alternative wintering options, which might have implications for their survival when facing habitat change or loss (e.g., like severe beach erosion as can be the case at one of the study sites)

Data from: Natal habitat and sex-specific survival rates result in a male-biased adult sex ratio

The adult sex ratio (ASR) is a crucial component of the ecological and evolutionary forces shaping the dynamics of a population. Although in many declining populations ASRs have been reported to be skewed, empirical studies exploring the demographic factors shaping ASRs are still rare. In this study of the socially monogamous and sexually dimorphic Black-tailed Godwit (Limosa limosa limosa), we aim to evaluate the sex ratio of chicks at hatch and the subsequent sex-specific survival differences occurring over three subsequent life-stages. We found that, at hatch, the sex ratio did not deviate from parity. However, the survival of pre-fledged females was 15-30% lower than that of males and the sex-bias in survival was higher in low quality habitat. Additionally, survival of adult females was almost 5% lower than that of adult males. Because survival rates of males and females did not differ during other life-history stages, the adult sex ratio in the population was biased toward males. Because females are larger than males, food limitations during development or sex-specific differences in the duration of development may explain the lower survival of female chicks. Differences among adults are less obvious and suggest previously unknown sex-related selection pressures. Irrespective of the underlying causes, by reducing the available number of females in this socially monogamous species, a male-biased ASR is likely to contribute to the ongoing decline of the Dutch godwit population.,Data_Capture_Recapture_Survival_AnalysisCapture-recapture dataset used for the survival analysis. CR-history contains two digits per year, first digit is only used when individual was ringed as chick. Further details explained in file.Data_Hatching_Sex_RatioDataset containing all chicks from complete nests and used to calculate sex ratio at hatch. All details are explained in file.