Burrowing Owl Offspring Sex Ratios: Long-Term Trends and a Test of the Triver and Willard Hypothesis

Publication Date


Type of Culminating Activity


Degree Title

Master of Science in Raptor Biology



Major Advisor

James R. Belthoff


This thesis consists of two chapters presenting results of investigations of burrowing owl (Athene cunicularia) offspring sex ratios. The objectives of my research were to (1) determine iflong-term trends in burrowing owl offspring sex ratios are consistent with predictions of commonly tested hypotheses, and (2) manipulate parental condition in burrowing owls to determine if offspring sex ratios are altered as predicted by the Trivers and Willard (1973) hypothesis. I conducted my fieldwork during the spring and summer of 2003 and 2004 in the Snake River Birds of Prey National Conservation Area (NCA) and in adjacent private and Bureau of Land Management lands in southwestern Idaho. I performed laboratory work to determine the sex of nestlings during the fall and winter of 2003 and 2004 at Boise State University. Information contained in this thesis should be of particular interest to those investigating behavioral ecology in avian species and possible mechanisms of offspring sex ratio manipulation, as well as to resource agency personnel responsible for managing burrowing owls.

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