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

Abstract

of elaborate, cryptic, or concealed nests, distraction displays, and nest guarding (Simmons 1955, Ricklefs 1969, Slack 1976, Scott 1977). There is evidence, although anecdotal, that some species will attack nest predators (for examples see Nolan 1959, Zimmerman 1963, Pettingill 1976). This behavior differs from other forms of anti-predator adaptations in that birds are vulnerable to injury when attacking a predator. In this paper I report on an experiment dealing with the aggressive responses of breeding birds to nest predators in an oldfield habitat. The major predators in old fields seem to be snakes, although birds (e.g. Blue Jays, Cyanocitta cristata) and small mammals cause some losses (Nolan 1963, Thompson and Nolan 1973, Best 1978, Gottfried and Thompson 1978). The study attempts to answer the following questions: 1) How prone are nesting birds to attack a nest predator? 2) Are nesting birds able to recognize nest predators, or do they indiscriminately attack any animal near their nests? 3) Do nesting birds respond differently to Blue Jays than to snakes? 4) Does the stage of the nesting cycle influence the intensity of anti-predator aggression?