干旱区生态环境知识资源中心

Insectivorous passerines were trapped during autumn and spring migration in an 0.02 km2 Sinai desert oasis 300 km south and 2000 km north of the northern and the southern edges of the birds’ cross-desert route. Mean number of recaptures and mean number of days between first and last captures were used for estimating the lengths of common species’ stopover periods and the size of their stopping-over populations, assuming a constant probability of staying an additional day and a constant daily probability of capture. Ca 80% of the birds were captured only once, and probably stayed one day. Species’ mean observed and estimated stopovers ranged from 1 to 5 d and 1.5 to 13.6 d, respectively. More birds stopped-over, and stopovers were on the average longer, (a) in autumn than in spring, (b) in early than in late autumn, (c) in late than in early spring, (d) in species and seasons with large stopping-over populations, (e) in females than in males (in two species with sexual dimorphism) in spring, and (f) in species encountering the oasis early on their autumn route than in species reaching it late. We propose that numbers alighting and stopover lengths depend on when and where an oasis is encountered. Birds tend to overfly oases or to stop for only one day either when the oasis is close to the point of migration initiation or when it is advantageous to reach breeding territories fast.