Data from: Long-distance dispersal is asymmetrical with respect to age, sex and breeding latitude in a long-lived monogamous bird

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.