NEST CONCEALMENT AND PREDATION IN HOODED WARBLERS - EXPERIMENTAL REMOVAL OF NEST COVER

It is commonly assumed that passerine birds with open nests reduce the risk of predation by concealing their nests. At a forest study site i n northwestern Pennsylvania, about 50% of the Hooded Warbler (Wilsonia citrina) nests were depredated-the primary cause of reproductive fail ure. To test the hypothesis that concealed nests are less likely to be depredated than conspicuous nests, we examined seven characteristics of the warbler's nest and nest microhabitat in relation to nest predat ion: nest visibility, vegetation density surrounding the nest, height of nest, height of nest substrate, nest-substrate species, height of c ryptic dead-leaf base of nest, and proximity of nest to a microedge. S uccessful and depredated nests (n = 97) did not differ in any of these variables. In addition, we performed a vegetation-removal experiment in which manipulated nests (n = 15) with surrounding vegetation remove d were on average 86% more visible overall than control nests (n = 15) . The highly visible manipulated nests did not suffer higher predation than control nests. Contrary to our hypothesis, our results show that nest concealment is not an important factor in predator avoidance for Hooded Warblers. This outcome would be expected if nest predation is the result of nonspecialist predation that occurs by chance and is bas ed on the location of available food in general.