Annual survival of Sparrowhawks Accipiter nisus breeding in three areas of Britain
Annual survival of breeding female Sparrowhawks Accipiter nisus was estimated by a capture-recapture procedure in three different areas, Eskdale and Annandale in southern Scotland and Rockingham Forest in east-central England. In Eskdale, where the breeding population remained fairly stable during a 19-year study, annual survival averaged 59% (s.e. = 4%). In Annandale, where the breeding population declined during a 10-year study, annual survival averaged 66% (s.e. = 4%). In Rockingham, where the breeding population increased during an 11-year study, annual survival averaged 72% (s.e. = 4%). In this area, survival declined during the study as numbers rose. The apparent density-dependence in survival was therefore confounded with a time trend. In all three areas, annual variations in survival were negatively related to the number of rain days during October-April, but the relationship was significant only in Eskdale. This area had the longest run of data and the greatest variation in the number of winter rain days. The relationship with rain days could partly account for the differences in mean survival between areas, with lowest survival in the wettest area and highest survival in the driest.