Threat from deforestation to montane and lowland birds and mammals in insular South-east Asia

1. A reduction in forest area should result in a reduction of its number of species and, moreover, do so in a characteristic way according to the fami liar species-area relationship. Brooks, Pimm & Collar (1997) applied this f ormula to the losses in forest area in the Philippines and Indonesia. Indep endently derived totals of the number of endemic bird species that are thre atened with extinction broadly agree with these predicted losses. In some c ases, however, predicted losses overestimate or underestimate the actual nu mbers of threatened species. 2. Within an island, the proportionate deforestation to date might be most extensive where there are many endemic species, or where there are few. To test this possibility, we obtained recent forest cover data for the region. We separated lowland (( 1000 m a.s.l.) from montane (> 1000 m a.s.l.) fore st cover by overlaying topographic maps. From these data, we predict separa tely the numbers of montane and lowland endemic bird species likely to beco me extinct as a result of deforestation. We then compared these totals with the numbers considered threatened in the latest Ren List. 3. Our predictions based on deforestation closely match the numbers of thre atened endemic birds in the lowlands, but underestimate them in montane reg ions. 4. Our predictions based on deforestation underestimate the number of threa tened montane mammal species even more seriously. 5. Lowland faunas of insular South-east Asia are under extreme threat becau se of massive deforestation. The region's montane faunas appear seriously t hreatened even by low levels of deforestation.