Population trend and status of the endangered White-backedWoodpecker Dendrocopos leucotos in Finland

摘要

White-backedWoodpecker Dendrocopos leucotos is an endangered specialist of mature deciduous forest inmany European countries, including Finland. The Finnish population declined severely during the 20th century. We studied the population development and demographic parameters in Finland during recent decades. According to winter counts, the population has been the lowest in 1980-1990s before the recent population increase. Both breeding success (study years 1991-2010) and the number of migrants (1979-2010) arriving from the east, have recently increased significantly. The sex ratio of migrants was female biased. The probability of detected occupancy of breeding pairs, other pairs and occupied territories (at least one individual observed) increased strongly during 1991-2010 especially in the eastern part of the country. Thus, the ca. 300-400% increase in numbers observed is not solely due to the increased number of monitored sites. The proportion of detected occupancy was also higher on territories considered as high-quality habitat.Number of autumnmigrants positively affected the territory occupancy in the following spring, but not the occupancy of pairs or confirmed breeders. Nevertheless, despite the positive trend in the intensity of irruptions, therewas a strong additional positive trend in occupancy that was independent from the effect of immigration.