The spring stopover of the reed warbler Acrocephalus scirpaceus in northeast Spain

Abstract

The patterns of spring stopover of the Reed Warbler Acrocephalus scirpaceus were investigated at a coastal site in northeast Spain between 1993 and 1997. Birds arrived in good physiological condition, with a mean fat load of 10%. There was a seasonal decline in wing length and fat load, suggesting that larger and fatter birds migrate earlier. Only 4.3% of the birds stopped over for more than one day. These birds carried lower fat loads and had a later capture time than transients. In addition they tended to show no increase in mass during their stopover although this can be an effect of birds in different stages of their migratory journey. Birds at our site had a mean stopover length of one day, enough to gain sufficient fat stores to reach the next feeding site. This strategy may be expected in spring, when birds are under selection pressure to minimize migration time.