Bird Survival in an Isolated Javan Woodland: Island or Mirror?

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Abstract
Differential extinction of forest species following forest fragmentation raises the questions of which populations are most prone to disappeaq and why. Hence we studied an 86–hectare woodland in west Java, the Bogor Botanical Garden (BBG), that became isolated when suwounding woodland was destroyed 50 years ago. Out of 62 bird species breeding in the BBG during 1932–1952, 20 had disappeared by 1980–1985, four were close to extinction, and five more had declined noticeably. The two main variables that identifl extinction‐prone populations in the BBG are 1) small initial population size in the BBG and 2) rareness or absence in the surrounding counttyside. Although the BBG retained wooded habitat, it is evidently too small to retain self‐sustaining populations of many woodland bird species. Small populations at high risk of extinction for stochastic reasons are doomed to disappear permanently unless subsidized by re‐colonization from the surroundings Thus, a too‐small reserve cannot function as a distributional island but comes to mirror the species composition of its surroundings More such case studies documenting species losses from small habitat fragments are required to demonstrate to nonbiologists the need for reserves large enough to support self‐sustaining populations.