SEX-DIFFERENCES IN THE STOPOVER ECOLOGY OF CURLEW SANDPIPERS CALIDRIS-FERRUGINEA AT A REFUELING AREA DURING AUTUMN MIGRATION

We investigated the stopover patterns of male and female Curlew Sandpi pers at a stopover area in northeast Spain. Curlew Sandpipers were tra pped and colour-ringed during autumn migration in 1992 and 1993. Stopo ver length was similar to those reported previously for this and other waders that migrate using a small number of widely separated staging areas, but were greater than stopovers reported for other tenders that migrate using it large number of staging areas separated by short dis tances. The differences in stopover length between the birds using the se two strategies could be related to the fuel reserves that have to b e accumulated to reach the next staging area. Males stayed longer in t he area than females. Seasonal changes in prey availability or sex dif ferences in moulting and migratory patterns do Mot account far these d ifferences in stopover ecology. Following a time-selected model of opt imal migration, sex differences in stopover ecology could be related t o a dominance of the larger females over the males or to a higher fora ging efficiency or a shorter search and settling time in females. Whet her these differences are restricted to the studied area or are widesp read in other staging areas used by the species could be important for assessing the possible differences in the migration speed of Curlew S andpipers. The finding that males leave the breeding grounds 21-35 day s before females but arrive at the study area with only a 10-day diffe rence supports the hypothesis that females migrate faster than males a t least in the first half of their migration.