干旱区生态环境知识资源中心

Length of stopover and rate of weight change were studied in Blackcaps that stopover in Eilat (southern Israel) in spring after a trans-Saharan flight. The birds studied had already completed 2000 km of desert crossing and faced just 200 km more. The potential predicted flight range for these transients suggests that the fat depleted Blackcaps (fat class=0) could not reach the east Mediterranean scrublands, which offer more extensive foraging opportunities than the desert area around Eilat, without refueling. However, 46% of the Blackcaps had sufficient fat (fat class>0) to reach central or northern Israel in a single flight in still air. Recaptured birds stayed in Eilat for 2,4+/-1,9 days. Although the body mass of an average recaptured bird increased by 0,27+/-1,44 g/day, which was an increase of 0,8%+/-7,0% of its body mass per day during stopover, these results were not significantly different from zero. Stopover length, mass change during stopover, and the rate of change in mass did not differ between males and females and between those who stopped over for only one day to those which stayed >1 day: However, there was a tendency of these lean birds to stay for a shorter period in Eilat than relatively fat birds. There was also some tendency for lean birds to gain more mass during their stopover than fat birds. It seems that in spring, when less time is allotted for the whole migration program, the migrants resume their journey before fat reserves have been replenished.