Although studies of bird biogeography in insular Southeast Asia using molecular methods are increasing in number, our understanding of bird evolution in the region is still poor. Among the dynamics that are especially intriguing and unknown is the interplay of populations between oceanic and continental islands. One example of this interaction is between continental Borneo and Maratua, a small oceanic island off its east coast. Birds on Maratua are morphologically highly differentiated from their counterparts on Borneo, despite close proximity, and most are in different subspecies based on descriptions in the 1930s. Here we provide genetic comparisons of 3 particularly distinct taxa: Black-headed Bulbul (Pycnonotus atriceps), Black-naped Monarch (Hypothymis azurea), and White-rumped Shama (Copsychus malabaricus). These comparisons show conclusively that the birds on Maratua are different species than their Bornean counterparts, and their marked differentiation is probably a function of founder effects and continued small population sizes.
