Migrating Lesser Spotted Woodpeckers Dendrocopos minor along the coast of southern Norway: Where do they come from?

摘要

The Lesser Spotted Woodpecker (Dendrocopos minor) is a partial migrant in Fennoscandia, where migratory autumn irruptions outside the regular breeding areas occur in some years. Little is known about the migration of this species along the coast of southern Norway, but such migrants might have an eastern origin. We evaluated this hypothesis, and the possibility that birds come from a more local population, by correlating the numbers ringed at Lista Bird Observatory with breeding-population indices from three regions: Sweden, M?re og Romsdal and Agder. Overall, 99 birds were trapped and ringed at Lista in autumn during 1989-2008 (median = 3.5, range 0-19). We found no correlation between numbers caught at Lista and the population indices from M?re og Romsdal. There was, however, a significant positive correlation between Lista numbers and the population index from the local Agder region. Breeding-population indices from Sweden were acquired from (1) long-term (1975-2009) summer point counts in observer-chosen, routes, and (2) a combination of point counts and line transects along fixed routes systematically distributed across the country (1998-2008). Population trends differed somewhat between these two methods, the latter indicating an increasing population size whereas the former showed a more stable situation. The fixed-routes data were positively correlated with Lista catch numbers, whereas the indices from summer point counts were not. These results suggest that migrating Lesser Spotted Woodpeckers captured in autumn at Lista Bird Observatory may come from an extensive area in Scandinavia, including more local regions. There was no sex bias in the captured birds, but 98% were in their first year. Hence, migration intensity probably reflects reproductive output in source populations.