Living on the edge: Variable responses of bird communities to edges in a tropical montane forest

With increasing disturbance in tropical forests, determining the effects of forest edges on biotic communities is essential.  The fauna of Monteverde, Costa Rica is diverse and endemism is high.  Many bird species have very limited geographic ranges and small local populations.   A pronounced moisture gradient on the Pacific slope harbors tree and bird communities that change dramatically within a few kilometers of the continental divide.   We documented the responses of the highland bird communities to forest edges.  Extensive point count surveys (550 surveys; 6586 detections; 115 species in 10km²) show that bird communities have variable responses to forest edges along the altitudinal and moisture gradients. Communities close to the continental divide (high elevation) show strong responses to forest edges and many endemic species avoid forest edges; edge effects further from the continental divide (lower and drier) are not pronounced.   Some cosmopolitan species are edge specialists or show no preference between edge and interior forest areas.  Our results demonstrate how bird communities can have varying responses to forest edges under different moisture regimes and in different forest types (cloudforest and rainshadow).  We suggest further testing of the idea that edge effects will depend upon how well adapted species already are to hot, dry conditions, as in tropical dry forest.  Forest edges emulate the conditions (hotter and drier) that are expected to result from climate change in many tropical regions, so that current community responses to edge conditions might forecast responses to future regional climate change.