Effects of Height and Vegetation on Success of Bird Nests in Maritime Forests

Nest predation is an important source of mortality in songbirds and may contribute to declines in Neotropical migrants. I used artificial nests baited with fresh Japanese Quail and Zebra Finch eggs in conjunction with observations of natural nests to quantity the ettects ol nest height and vegetation on nest predation on St. Catherine\u27s Island, a barrier island in southeast Georgia. Because of intense browsing by white-tailed deer. I predicted that lower, more exposed nests would be least successful. Artificial nests (n = 389) were placed in the field, and natural nests (n = 49) were observed, durintz April and May 1999 - 2000. Natural nests were more likely to be successful (77.6%: 38/49) than artificial nests (49.9%; 194/389). Nest success decreased with nest height in artificial nests, but height did not affect natural nests. Successful nests tended to ha\e more vegetation cover horizontally within 1 m of the nest; this effect was most pronounced in artiticial nests. I he effects of vegetation were consistent across nest heights. Patterns of egg loss suggest that most nest predation was by larger nest predators, but smaller predators (such as mice or small snakes) appeared important at lower nest heights. Overall, lower nests were not less successful on St. Catherine\u27s Island, but vegetation cover was important to nest success. Deer browsing does not appear to be causing unusual mortality in songbird nests below 2 m. but passerines on St. Catherine\u27s Island tended to select nest sites non-randomly to minimize detection b\ predators. Although shrub-nesting passerines were able to find suitable nest sites in this study, the effects of browsing on the habitat may limit the number of available nest sites, thus decreasing the ov erall population of Neotropical migrants on St. Catherine\u27s Island. Because the majority of Neotropical migrants nest in the shrub layer and are more prone to the effects of nest predation. Future research should assess the effects of populations of white-tailed deer on vegetation in southeastern maritime forests