Search

Which factors shape animals’ migration movements across large geographical scales, how different migratory strategies emerge between populations, and how these may affect population dynamics are central questions in the field of animal migration [1] that only large-scale studies of migration patterns across a species’ range can answer [2]. To address these questions, we track the migration of 270 Atlantic puffins Fratercula arctica, a red-listed, declining seabird, across their entire breeding range. We investigate the role of demographic, geographical, and environmental variables in driving spatial and behavioral differences on an ocean-basin scale by measuring puffins’ among-colony differences in migratory routes and day-to-day behavior (estimated with individual daily activity budgets and energy expenditure). We show that competition and local winter resource availability are important drivers of migratory movements, with birds from larger colonies or with poorer local winter conditions migrating further and visiting less-productive waters; this in turn led to differences in flight activity and energy expenditure. Other behavioral differences emerge with latitude, with foraging effort and energy expenditure increasing when birds winter further north in colder waters. Importantly, these ocean-wide migration patterns can ultimately be linked with breeding performance: colony productivity is negatively associated with wintering latitude, population size, and migration distance, which demonstrates the cost of competition and migration on future breeding and the link between non-breeding and breeding periods. Our results help us to understand the drivers of animal migration and have important implications for population dynamics and the conservation of migratory species.

This report addresses changes in population size in five species of diving ducks breeding and wintering in the Baltic Sea. Declines in breeding Greater Scaup, Eider and Velvet Scoters on the Baltic coast are verified. Long-tailed Ducks and Eiders have declined in winter. Breeding Eiders have declined in Norway. Monitoring programs in all Nordic countries are partly inadequate for detecting changes in numbers of birds both in winter and during breeding, but large-scale trends appear reliable. The reasons for the declines observed are largely unknown. For breeding Eiders in the northern part of the Baltic Sea a change in predation regimes on the breeding islands may be important. If the negative trends are to be stopped, a deeper understanding of the drivers involved and better knowledge about the ecological status of the Baltic Sea food webs utilized by the diving ducks are needed.

Zoologi, fugle, Tanzania