Anti-Predator Aggression in Birds Nesting in Old Field Habitats: An Experimental Analysis

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Abstract
The likelihood of breeding birds defending their nests against models of known nest predators was studied. In a series of experiments, nesting birds responded differently to models of jays, snakes and sparrows. Catbirds [Dumetella carolinensis] and thrashers [Toxostoma rufrum] were more aggressive toward the snake model than the mounted jay, while cardinals [Cardinalis cardinalis] and robins [Turdus migratorius] were passive. The intensity of antipredator aggression differed during stages of the breeding cycle. Catbirds and thrashers were more aggressive toward the jay model after hatching than before, while robins attacked the snake model only during the post-hatching period. The intensity of anti-snake behavior was positively correlated with clutch size in 3 of 4 spp. tested.