Population status and distribution of Taita White-eye Zosterops silvanus in the fragmented forests of Taita Hills and Mount Kasigau, Kenya

摘要

Our study focused on the Taita White-eye Zosterops silvanus, one of three bird species endemic to the Taita Hill forests, south-east Kenya. Formerly considered Critically Endangered, Taita White-eye has been down-listed to Endangered following the findings of this study. Between November 1998 and September 1999 we counted this species along line transects to establish their current population status and distribution in its entire range. White-eye censuses were conducted in nine forest fragments of the Taita Hills and the virtually undisturbed Mt Kasigau forest. The total global population of Taita White-eyes was estimated to be c. 7,100 birds. Mt Kasigau was shown to be the species' main stronghold, maintaining a very high density (26 birds ha(-1)) and holding 80% (5,600 individuals) of the entire population. In the Taita Hills forests, densities were consistently higher in the small isolated fragments than in the large ones, though the former held only a small population (3% of total). At Mt Sagala, a large isolated block where indigenous trees have been largely replaced with exotic plantation, this species was not encountered. We found no evidence of interchange between the White-eye populations on Mt Kasigau and the Taita Hills forests, probably because of the separation by a low-altitude, dry woodland habitat barrier. While prioritization for conservation action should focus more on the Taita Hills forest fragments, Mt Kasigau should be treated as fragile ecosystem which holds a huge, apparently insular population of Taita White-eyes.