Age-related stopover strategies in the Wood Sandpiper Tringa glareola

Abstract

Wood Sandpipers have been trapped between the years 2000 and 2003 during their au- tumn migration at Hohenau, in the north-east of Austria. Birds seem to deposit fat reserves continually throughout a small step migration across Central Europe; hence Wood Sand- pipers need a large number of stopover sites to continue migration. Fat score of the birds increases as the season progresses at Hohenau, which may be an insurance against any de- terioration of food supply as the time available for migration decreases. Strong evidence was found that adults and juveniles use different migration strategies: adults possessing higher body mass and thus carrying higher fat loads than juveniles. The juveniles are therefore forced to spend more time feeding and in consequence are more vulnerable both to a deterioration of food supply and to predation. Juveniles seem to avoid competition with each other. Transient juveniles may be adapted to migrate in longer stages than tem- porary residents. Potential flight ranges were calculated, suggesting that most of the birds, especially the juveniles, need additional staging sites before crossing the Mediterranean Sea and the Sahara.