Data from: Survival varies seasonally in a migratory bird: linkages between breeding and non-breeding periods

1. Migratory species form an important component of biodiversity; they
link ecosystems across the globe, but are increasingly threatened by
global environmental change. Understanding and mitigating threats requires
knowledge of how demographic processes operate throughout the annual
cycle, but this can be difficult to achieve when breeding and non-breeding
grounds are widely separated. 2. Our goal is to quantify the importance of
variability in survival during the breeding and non-breeding seasons in
determining variation in annual survival using a single population and,
more broadly, the extent to which annual survival across species reflects
variation in probability of surviving the migratory period. 3. We use a 25
year dataset in which individuals of a long-distance migratory bird, the
alpine swift Tachymarptis melba, were captured towards the beginning and
end of each breeding season to estimate age- and season-specific survival
probabilities and incorporate explicit estimation of the correlations in
survival between age-classes and seasons. 4. Monthly survival was higher
during the breeding period than during the rest of the year and strongly
affected by conditions in the breeding season; effects that remained
apparent in the following non-breeding season, but not subsequently.
Recruitment of juveniles was dependent on the timing of breeding, being
higher if egg-laying commenced before the median date, and substantially
lower if not. 5. Across migratory bird species, variation in annual
survival largely reflects variation in the probability of surviving the
migratory period. Using a double-capture approach, even within a single
season, provides valuable insights into the demography of migratory
species, which will help understand the extent and impacts of the threats
they face in a changing world.