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Measures to boost populations can help ensure population persistence in the short‐term while longer‐term conservation interventions take effect. Headstarting, involving the collection of wild early life‐stage individuals, rearing in captivity, and release into a new or existing population once independent, has recently been identified as a potential translocation technique to assist small breeding populations of waders declining due to low levels of productivity. However, the demographic rates of headstarted individuals have not been quantified, and their impact on target populations not understood, which is required to determine the efficacy of this technique as a tool for species recovery. Between 2017 and 2022, headstarting was trialled as a tool to supplement the critically small sub‐population of black‐tailed godwit (Limosa limosa limosa) breeding at the Ouse Washes, Eastern England. We demonstrate that a high survival rate for eggs and chicks can be achieved through artificial incubation and hand‐rearing, and that headstarting can substantially increase the overall productivity of a small population. Using survival analysis and mixed effects modelling, we show that apparent survival and breeding success of headstarted individuals is comparable to wild‐reared conspecifics. The survival rate of released birds was sufficient to significantly boost the breeding population, reaching over five times the number of breeding pairs at the release site during the trial. Providing demographic rates remain the same, the number of godwits breeding at the Ouse Washes is predicted to continue to increase moderately over the next 20 years. This study highlights the potential of headstarting to boost small populations of breeding waders, and demonstrates the value of this technique to assist with the recovery of threatened populations when there is a clear justification that headstarting can negate the effects of population limiting factors. [ABSTRACT FROM AUTHOR]

Long‐distance migratory flights are predicted to be associated with higher mortality rates when individuals encounter adverse weather conditions. However, directly connecting environmental conditions experienced in‐flight with the survival of migrants has proven difficult. We studied how the in‐flight mortality of 53 satellite‐tagged Black‐tailed Godwits (Limosa limosa limosa) during 132 crossings of the Sahara Desert, a major geographical barrier along their migration route between The Netherlands and sub‐Saharan Africa, is correlated with the experienced wind conditions and departure date during both southward and northward migration. We show that godwits experienced higher wind assistance during southward crossings, which seems to reflect local prevailing trade winds. Critically, we found that fatal northward crossings (15 deaths during 61 crossings) were associated with adverse wind conditions. Wind conditions during migration can thus directly influence vital rates. Changing wind conditions associated with global change may thus profoundly influence the costs of long‐distance migration in the future. [ABSTRACT FROM AUTHOR]

Sexual size dimorphism ( SSD) is common in birds and has been linked to various selective forces. Nevertheless, the question of how and when the sexes start to differentiate from each other is poorly studied. This is a critical knowledge gap, as sex differences in growth may cause different responses to similar ecological conditions. In this study, we describe the sex-specific growth - based on body mass and five morphometric measurements - of 56 captive Black-tailed Godwit Limosa limosa limosa chicks raised under ad libitum food conditions, and conclude that all six growth curves are sex-specific. Females are the larger sex in terms of body mass and skeletal body size. To test whether sex-specific growth leads to sex-specific susceptibility to environmental conditions, we compared the age-specific sizes of male and female chicks in the wild with those of Black-tailed Godwits reared in captivity. We then tested for a relationship between residual growth and relative hatching date, age, sex and habitat type in which the wild chicks were born. Early-hatched chicks were relatively bigger and in better condition than late-hatched chicks, but body condition and size were not affected by natal habitat type. Female chicks deviated more negatively from the sex-specific growth curves than male chicks for body mass and total-head length. This suggests that the growth of the larger females is more susceptible to limiting environmental conditions. On average, the deviations of wild chicks from the predicted growth curves were negative for all measurements, which suggests that conditions are limiting in the current agricultural landscape. We argue that in estimating growth curves for sexually dimorphic species, it is critical first to make accurate sex and age determinations. [ABSTRACT FROM AUTHOR]