PARENT SESSION
Oral Session #23: Animal Ecology: Behavior and Sociobiology. Presiding: P. Brunkow.
Tuesday, August 7, 2001. 8:00 AM to 11:45 AM. Hall of Ideas E.
Parental behavior of a Cowbird host: Caught between the costs of egg-removal and nest predation.
Tewksbury, Joshua1,2, Martin, Thomas2,3, Hejl, Sallie4,5, Kuehn, Michael6, Jenkins, Wajid2, 1 2 3 4 5 6
ABSTRACT- Avian brood parasites reduce host fitness through removal of host eggs. Egg-removal can be an important source of natural selection because brood parasites remove eggs from virtually all hosts they parasitize and egg-removal constitutes the primary fitness cost of parasitism for some hosts. Yet, host responses to egg-removal are relatively unstudied. Through experimental manipulations and observations, we demonstrate here that female Yellow Warblers (Dendroica petechia) respond to the threat of egg-removal by Brown-headed Cowbirds (Molothrus ater) by spending more time on the nest (increased attentiveness). This behavior reduced egg-removal by cowbirds, as cowbirds rarely forced sitting females off their nests, and females that do not lose eggs to cowbirds had significantly higher attentiveness. Increased female attentiveness, however, reduces time for females to gather food and requires males to visit the nest more often to feed incubating females. Indeed, female attentiveness was highly correlated with male incubation feeding rate, regardless of parasitism. The increased activity by males associated with higher nest attentiveness in turn increased the risk of nest predation, such that experimentally parasitized nests had significantly higher daily predation rates during incubation and early nestling development than control nests. Thus, brood parasitism and nest predation may produce conflicting selection on incubation strategies, as parasitized hosts are caught between the costs of egg-removal by brood parasites, and the costs of increased nest predation if the female spends more time on the nest to reduce egg-removal.
KEY WORDS: brood parasitism, nest predation, incubation behavior, yellow warbler