Phenology of migration and use of wintering sites by the increasing population of dark-bellied brent geese Branta bernicla bernicla



During the recovery of the population of dark-bellied brent geese Branta bernicla bernicla, traditional wintering sites in Britain have experienced increases in numbers and new sites have been colonized. Goose counts were used to describe the migration phenology and winter use of Scolt Head, north Norfolk (a traditional site) and the Burry Inlet, South Wales (a relatively new site) over the period of re-colonization and colonization, respectively. During the 1950s, only a few hundred birds wintered at Scolt Head, and most stayed for only a short period. By the late 1980s/early 1990s, numbers had reached several thousands, their period of stay was longer and there was little variation between years in median arrival (28 October) and departure (11 March) dates. A similar process was observed during the entire colonization phase at the Burry Inlet; initially birds arrived late and departed early, but arrived progressively earlier and departed later as wintering numbers increased. The autumn arrival rates at both sites were slower than the spring departure rates. During years of good breeding productivity, those adults with young arrived slightly later in Norfolk than failed breeders and non-breeders, and a higher proportion of young birds remained in spring after the main departure. However, the overall pattern of arrival and departure did not vary according to whether there had been a good or poor breeding season. Some adults of breeding age also remained until May. The effects of food depletion and use of novel feeding habitats in relation to migration phenology and winter use of sites are discussed.