An avifaunal study of Pigeon Valley Park as a biogeographic island in an urban area with special reference to the Natal Robin (Cossypha natalensis Smith)
Boon, Richard Graham Campbell.
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Pigeon Valley Park, on Durban's Berea Ridge, is an approximately 10-ha remnant of coastal forest, which is totally surrounded by suburban housing and roads. As such it is ideal as a study area for investigating the applicability of the MacArthur-Wilson Theory of Island Biogeography (1963,1967) and Diamond's (1975) geometric reserve-design principles to fragmented Coastal Forests in Durban. This study began in January 1989 and the results are reported as at October 1992. Field notes from as far back as 1981 were used to augment the findings of the current work. Research focused on the forest-dwelling, Natal Robin Cossypha natalensis, and territory mapping showed that the reserve supports up to 53 individuals during the breeding season. An annotated checklist and its comparison to historical and regional checklists revealed where localised extinctions may have occurred, and thus identifies a set of coastal forest species which are susceptible to habitat fragmentation. Work on two potential dispersal corridors for bird movement into and out of the valley showed that the reserve is not yet fully isolated to most species which are currently present. On the other hand, there are some forest species which have isolated populations at Pigeon Valley Park, as well as others which do not seem able to establish and maintain viable populations. A set of 'indicator', forest bird species which are susceptible to habitat fragmentation, is defined. Practical management suggestions with the aim of increasing the long-term viability of the area as an avifaunal preserve, are presented.