干旱区生态环境知识资源中心

African Black Oystercatchers Haematopus moquini are sedentary as adults. However, colour-ringing of more than 700 juveniles has revealed complex post-fledging movements that vary geographically. Young from the western part of the breeding range either remain within 150 km of their natal site or migrate 1500-2000 km to one of five discrete nursery areas on the Namib Desert coast of central and northern Namibia, and southern Angola. These nurseries all lie north of the species’ breeding range. We calculate that 36-46% of all juveniles born in South Africa migrate to nurseries. Birds return to their natal sites from nurseries at 2-3 years old, but never migrate again. Juveniles from the eastern part of the range undertake ’diffusion dispersal’, regularly up to 1000 km, but these journeys mostly end within the breeding range, where there are no nurseries. Very few eastern birds reach nurseries. There is no evidence that movements of western birds are density-dependent responses to hatching date, but long-distance migrants are significantly heavier as chicks than are short-distance dispersers. We hypothesize that a genetic basis exists to these movements, possibly triggered by body condition, that could account not only for the highly dichotomous behaviour of western birds, but also for the intermediate behaviour of eastern birds.