Predatory Identity Can Explain Nest Predation Patterns

Knowledge of dominant predators is necessary to identifY predation patterns and mitigate losses to nest predation, especially for endangered songbirds. We monitored songbird nests with timelapse infrared video cameras at Fort Hood Military Reservation, Texas, from 1997 to 2002 and 2005, and in Austin, Texas, during 2005, 2006, 2008, and 2009. Predation was the most common source of nest failure. We identified 13 species of predators during 126 predation events. Snakes were the most frequent nest predator group (n = 48), followed by birds (n = 25), fire ants (n = 22), cowbirds (n = 15), and mammals (n = 14). We evaluated models predicting probability of predation by five predator groups that represented two groups of hypotheses: temporal and nest activity factors, and habitat and landscape factors. Snake and fire ant predation primarily occurred at night, whereas bird predation occurred during the day. Mammal predation occurred during both day and night. Predicted nest predation by birds, cowbirds, and mammals decreased throughout the breeding season, but predation by fire ants Predation is often the leading cause of nest failure for passerines (Newton 1998, Thompson 2007). High predation rates can limit productivity of a population and have been implicated as a possible source of declining and snakes increased. Predation was highest on older nestlings (>6 days old) by all predator groups except fire ants, which depredated young nestlings more. The percent urban land class in the landscape and nest height affected predator groups at shrub and canopy nests differently. Bird and snake predation increased for canopy nesters with increasing urbanization and nest height. Cowbird predation increased for shrub nesters with increasing urbanization and nest height, and increased with greater percent of open land use in the landscape for both guilds. We found no good predictor of mammal predation, likely because small and meso-mammals were lumped. We suggest future investigations of nest predation either identifY predators, or at least consider who the likely predators are, and consider predator-specific hypotheses.