Fat‐weight relationships and migratory strategies in the RobinErithacus rubeculaat two stop‐over sites in south Sweden

Abstract

Robins captured during spring and autumn migration 1986 at Falsterbo and Ottenby, south Sweden were compared as to fat deposition, body weight and size (measured as wing length). Though the birds from the two sites were of practically the same size, significant differences in fat deposition and body weight were found. The Robins captured at Falsterbo were heavier but carried less fat than the Ottenby Robins. The differences were more obvious in the lower fat classes in autumn birds, more constant through all fat classes in spring birds. These results indicate that Robins from the two sites use different migration strategies. Probably, many Falsterbo Robins are “short‐stage migrants”, travelling over land, and needing only small fat reserves, while the Ottenby Robins are “long‐stage migrants” needing large fat reserves to complete their flight across the Baltic Sea. This pattern fits in well with other studies on Robins from the two sites (reports of ringed birds, orientation experiments). We also speculat...