Data from: Exploiting the richest patch has a fitness pay-off for the migratory swift parrot

1. Unlike philopatric migrants, the ecology of nomadic migrants is less
well understood. This life-history strategy reflects responses to
spatiotemporal variation in resource availability and the need to find
resource rich patches to initiate breeding. The fitness consequences of
movements between regions of patchily distributed resources can provide
insight into ecology of all migrants and their responses to global change.
2. We link broad-scale data on spatiotemporal fluctuation in food
availability to data on settlement patterns and fitness outcomes for a
nomadic migrant, the endangered swift parrot Lathamus discolor. We test
several predictions to determine whether facultative movements are
adaptive for individual swift parrots in an environment where resources
are patchily distributed over time and space. 3. Variation in the
availability of swift parrot food resources across our study period was
dramatic. As a consequence, swift parrots moved to breed wherever food was
most abundant and did not resettle nesting regions in successive years
when food availability declined. By moving, swift parrots exploited a
variable food resource and reproduced successfully. 4. Exploiting the
richest patches allowed swift parrots to maintain stable fitness outcomes
between discrete breeding events at different locations. Unlike sedentary
species that often produce few or lower quality offspring when food is
scarce, nomadic migration buffered swift parrots against extreme
environmental variation. 5. We provide the first detailed evidence that
facultative movements and nomadic migration are adaptive for individuals
in unpredictable environments. Our data support the widely held assumption
that nomadic migration allows animals to escape resource limitation.