Turnover of individuals in a local population of Pink-footed Geese Anser brachyrhynchus

摘要

The turnover of individually neck-collared Pink-footed Geese Anser brachyrhynchus was measured at the Loch of Strathbeg, Grampian, Scotland, from September to mid-November, 1999—2002. The observations, carried out from hides near the birds' roostingsites, were shown to sample the local population reasonably randomly and to detect 62% of the marked birds in the area. The proportion of 'new' individuals, not seen previously in the same autumn, stabilised at around 40%, suggesting strongly that therewas a turnover of individuals. Most individual geese stayed in the area for a minimum period of only a few weeks, and about one third were seen elsewhere in the UK during the autumn study period. The proportion of geese with collars decreased from September to November, more steeply in 2000 than in 2001 or 2002. The first sighting dates of individual birds were not correlated between years. The findings show that there was a high degree of turnover of individual geese at the site, suggesting that over one third of the whole population passes through Strathbeg, and that different components of the population might pass through the area at different times during the autumn. This has important implications for the measurement of productivity, particularlythe timing of sampling.