Autumn migration speed of juvenile Reed and Sedge Warblers in relation to date and fat loads

We analyzed speed of migration in two congeneric warblers, the Reed and the Sedge Warbler, Acrocephalus scirpaceus and A. schoenobaenus. Sedge Warbler s migrated at a higher speed than Reed Warblers. The two species showed sim ilar rates of fat deposition at our Swedish study site, although Sedge Warb lers departed with lower fat loads. The higher speed of migration in Sedge Warblers and their lower departure fat loads suggest that they encounter st opover sites which offer higher relative fat deposition rates farther south . The amount of visible fat at the time of banding was positively related t o the speed of migration. Estimates of speed of migration for the two speci es suggest that the recoveries were situated on average 76-111 km farther s outh per increase in fat score, corresponding to 58-85% of the expected dis tance a bird can cover by using the fuel of one unit of fat score.