Breeding success and changes in numbers of african black oystercatchers haematopus moquini in relation to habitat quality and protection status

Abstract

We studied populations and reproduction of African Black Oystercatchers in De Hoop Nature Reserve (DHNR), South Africa, during 1984- 1998. Densities of breeding birds were slightly lower than those in other mainland areas. Rocky/mixed habitat supported a relatively higher density of breeding pairs than mixed/sandy habitat. Although there was no difference in mean annual first clutch size (1.78), replacement clutches were larger in the central and eastern sectors (1.9 eggs) than in the western sector (1.2 eggs). Mean chick-raising success (0.82 fledglings/chick) was higher than mean hatching success (0.42 chicks/egg) in all sectors. Mean fledging success/pair varied from 0.68 to 0.85 over six years, among the highest recorded anywhere. The proclamation of De Hoop Marine Reserve, including the entire coast of the nature reserve (where angling and collecting intertidal organisms are prohibited), led to a decrease both in disturbance from off-road vehicles and in direct competition from humans for marine resources. These initial benefits were not sustained in terms of breeding success, however, possibly because of increased numbers of visitors to the coast, especially after 1991. In the central sector, where human disturbance was highest, most nest failure was human-related, whereas in the less disturbed eastern sector natural factors were more important. High site fidelity is supported by the fact that 21% of all birds ringed rejoined the breeding population between eight and 14 years later, a relatively high proportion (32%) of these birds returning in their second year. Numbers of adult African Black Oystercatchers increased significantly over the study period. Although numbers of juveniles per pair appeared to benefit initially from the proclamation of the marine reserve, they showed a cyclic and overall declining tendency over the 14-year study period. This trend may be related to the increasing numbers of human visitors to the coast. DHNR is regarded as an important site for the global African Black Oystercatcher population, and this long-term study contributes to the conservation of this relatively rare species.