Reproductive value and appropriateness of response to predators by White-Crowned Sparrows

Abstract

Twenty-five pair of breeding Whitecrowned Sparrows were presented with a live snake and models of a hawk, jay, and junco. Pairs were tested either when the female was brooding eggs, feeding nestlings, or fledglings. It was found that the snake was responded to the most when the pair had nestlings, very little when the female was brooding eggs, and at a moderate level with fledglings. The hawk and jay models were responded to the least with eggs, more with nestlings, and the most with fledglings. The junco model elicited little response. Both the pattern and level of response is influenced by whether or not the stimulus represents an effective predator at the particular stage of the breeding cycle. They also are influenced by the reproductive value of the progeny. A model is suggested that includes two factors: stimulus value and reproductive value. We propose that this combined model is more suitable than a single factor one.