Stopover and fat accumulation in passerine birds in autumn at Ottenby, southeastern Sweden

Abstract

Stopover duration and fat accumulation were studied during autumn migration at two sites near Ottenby, Öland, southeastern Sweden in 1985 and 1986. The species are Thrush Nightingale, Barred Warbler, Lesser Whitethroat, Whitethroat, Willow Warbler and Red-backed Shrike. We captured the birds in mist nets between 10 July and 20 August and recorded visually the fat class and measured the body mass. Post juvenile moult was scored on juvenile birds. In several of the species fat class and body mass increased with day of season (Thrush Nightingale, Barred Warbler and Whitethroat), while in the Lesser Whitethroat there was a reduction in fat class and body mass with day of season. Recaptures revealed that the highest daily increase in body mass was 2.7% in a Willow Warbler and a Red-backed Shrike, while a Barred Warbler showed a maximum daily body mass increase of 2.4%. The duration of stopover in migrants varied between 2 and 7 days.