Time lag between deforestation and bird extinction in tropical forest fragments

Tropical forests are becoming increasing fragmented, threatening the surviv al of the species that depend on them Small, isolated forest fragments will lose some of their original species. What is uncertain is how long this pr ocess of faunal relaxation will take. We compiled data on birds in five tro pical forest fragments in Kakamega Forest, Kenya, of known date of isolatio n. We then predicted the original and eventual species richness of these fr agments and, from this difference, the eventual species losses. Expressing the losses to date as a fraction of eventual losses suggests that faunal re laxation approximates an exponential decay with a half-life of approximatel y 50 years for fragments of roughly 1000 ha. In other words, in the first 5 0 years after isolation, tropical forest fragments of this size suffer half of the total number of extinctions that they are likely to experience. Thi s result sets the time scale over which humanity must take conservation act ion in fragmented tropical forests, may aid efforts to set priorities, and indicates how high the future global extinction rate will be.