APPARENT AVIAN EXTINCTIONS FROM ISLANDS IN A MAN-MADE LAKE, SOUTH AFRICA

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Abstract
Dean, W.R.J. & Bond, W.J. 1994. Apparent avian extinctions from islands in a man-made lake, South Africa. Ostrich 65:7-13. We surveyed avian diversity and abundance on islands in a 16 year old man-made lake in southern Africa. The vegetation was semi-arid shrubland and grassland. We compared species lists on islands with matched sites on the surrounding mainland. We recorded a total of only 19 species on islands, 25 on islands connected by landbridges to the mainland and 32 species on the mainland. Islands had significantly fewer species than their mainland airs but the difference was unrelated to island size. Three species (Fairy Flycatcher Stenostira scita, Redeyed Bulbul Pycnonotus nigricans, and Namaqua Dove Oena capensis) were common in mainland censuses but absent on islands. These species are insectivorous, frugivorous and granivorous respectively. Two species, Cape Sparrow Passer melanurus and Mountain Chat Oenanthe monticola, were more common on islands than mainland sites. Larger species and those with patchy mainland distributions were most prone to extinction on islands. This study shows that habitat fragmentation can cause rapid species loss, even in vagile groups such as birds. It points to the importance of recolonisation ability for predicting minimum viable areas. The persistence of species in habitat fragments may depend critically on corridors over which birds are willing to fly.