Migratory connectivity in Arctic geese: Spring stopovers are the weak links in meeting targets for breeding

Linking spring migratory itineraries of individual Arctic-breeding geese to their eventual breeding success has provided evidence that accumulation of body stores (protein, fat) at stop-over sites is crucial. We show that this is because geese nesting in the Arctic depend at least in part on these stores for synthesis of eggs and supporting incubation (for the female, a phase of starvation). Estimates of the body stores needed for successful reproduction (eggs + incubation) in relation to measured rates of accumulation of these stores make clear that meeting the demands solely by feeding at the breeding grounds is not an option for geese. The time constraint does not allow this, because early laying is a necessity in the Arctic to ensure survival of the progeny. Although the parents can exploit the early spring growth along the flyway, they get ahead of the wave of growth when they arrive on the breeding site and hence the parental timetable can only be met by drawing on body stores. Results from tracking studies in six goose species underline the conclusion that egg formation commences along the flyway before arrival at the nesting colony. In some cases, signatures of stable isotopes in egg components and parental body tissues in relation to the signature in forage plants support the notion of a mixed endogenous/exogenous origin. The close match between migratory timing and the spring flush of plant foods makes geese particularly vulnerable to the impact of climate change. There is an increasing mismatch along the NE Atlantic Flyway, where a warming trend in NW Europe conflicts with stable or even cooling trends in the Arctic target areas