Although relatively rare, long-distance dispersal significantly impacts population persistence by facilitating range expansion, range shifts, and genetic exchange. For individuals dispersing northwards, it may be a suitable adaptation strategy to escape negative effects of climate change on their original breeding sites. In this study, we constructed a joint live encounter – dead recovery model under a Bayesian multistate framework to quantify long-distance dispersal between the Barents Sea, Baltic Sea, and North Sea subpopulations of the Russia/Germany & Netherlands flyway population of barnacle goose (Branta leucopsis), using long-term mark-recapture data of 22,413 individuals ringed between 1995 – 2023. Long-distance dispersal was strongly biased by age-, sex- and direction. Natal dispersal predominantly occurred in northward direction with 23.9% of juvenile males and 8.6% of juvenile females estimated to transition annually from the North Sea to the Barents Sea subpopulation. In contrast, breeding dispersal in the same direction in adults was minimal, estimated at only 0.49% and 0.21% for males and females respectively, and was not always distinguishable from temporary (moult-) migrations. Our model results were validated with data from 14 dispersing individuals, 9 of which were male, for whom the timing of breeding or moult was recorded. In all cases, dispersal was in northward direction and timing of breeding or moult of dispersers more closely resembled the timing of the receiving than of the original subpopulation, but more so in males than in females. Our results support the notion of strong male-biased natal dispersal in monogamous waterbirds. Interestingly, despite substantial growth in the temperate breeding subpopulations during our study period, natal dispersal occurred predominantly in northward direction at both individual and population levels. The unidirectional long-distance dispersal observed is expected to result from the unique flyway structure, were subpopulations with large differences in population size mix during wintering. Additionally, we also highlight the adaptability of dispersers, showing that barnacle geese can adaptively switch migration on and off, and that plasticity in timing of breeding and moult may be larger in males than in females. We argue that this could be an additional explanation for the predominantly male-biased northward dispersal observed in barnacle geese.

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European Turtle Doves Streptopelia turtur have experienced a sharp decline in population numbers over past decades. Much uncertainty exists about the main cause or causes. Several pressures have been suggested, but because they affect different stages of the life cycle of the Turtle Dove, it is difficult to compare their contributions to population decline. Here we applied a full life cycle approach to study how different pressures may have resulted in the decline. This was achieved by combining a review of existing literature on possible threats, pressures, and the vital rates they concerned, with the analysis of an age-structured matrix model. The population model was parameterized using estimates from a mark-recapture analysis and supplemented with vital rate estimates from the literature. Comparison with a Life Table Response Experiment (LTRE) was used to determine whether the Turtle Dove literature focusses on those vital rates in which the most important changes have taken place over time. The population model projected a similar decline to that observed in population counts. The LTRE analysis showed that declines in the number of clutches (halved since the 1960s) and in juvenile survival (relative annual rate of change of -1.33% since the 1950s) contributed most to the decline in the projected population growth rate. Although these vital rates are often reported as possible causes of population decline, the reviewed studies often focused on specific reproductive stages, such as egg survival or nestling survival, which did not show a large temporal change. Thus, there is a partial mismatch between our modelling results and the focus in the literature. Juvenile survival is thought to be affected by hunting, degradation of wintering habitat and infection with Trichomonas gallinae, while loss of foraging habitat seems to affect the number of clutches. The focus of conservation measures should therefore be on these threats and pressures. The first steps have already been taken with completion of the international single species action plan for the conservation of the Turtle Dove and the implementation of the first conservation measures on the breeding grounds.