Adult Quality Indicators Underlying Sex Ratio Bias in American Kestrels
Faculty Mentor Information
Julie Heath
Abstract
In sexually size dimorphic animals, such as American kestrels (Falco Sparverius), the larger sex is more energetically expensive sex to raise to maturity. Sex ratios of offspring may be one way of ensuring reproductive effort is aligned with resources. The Trivers-Willard hypothesis predicts that parents with more resources and that are in better overall condition should produce more of the larger sex. In American kestrels, higher quality parents would be predicted to have more females compared to lower quality parents. We tested this hypothesis by evaluating whether American kestrel offspring sex ratios were associated with indicators of adult quality such as circulating concentrations of carotenoids, or nest initiation date. We monitored American kestrel breeding in nest boxes in the Treasure Valley and used historical data collected as part of a long term study. Preliminary results suggest that American kestrels may only show sex-biased ratios in some years. However, sex-biased ratios may be tied to one or more underlying influences including adult quality and environmental conditions.
Adult Quality Indicators Underlying Sex Ratio Bias in American Kestrels
In sexually size dimorphic animals, such as American kestrels (Falco Sparverius), the larger sex is more energetically expensive sex to raise to maturity. Sex ratios of offspring may be one way of ensuring reproductive effort is aligned with resources. The Trivers-Willard hypothesis predicts that parents with more resources and that are in better overall condition should produce more of the larger sex. In American kestrels, higher quality parents would be predicted to have more females compared to lower quality parents. We tested this hypothesis by evaluating whether American kestrel offspring sex ratios were associated with indicators of adult quality such as circulating concentrations of carotenoids, or nest initiation date. We monitored American kestrel breeding in nest boxes in the Treasure Valley and used historical data collected as part of a long term study. Preliminary results suggest that American kestrels may only show sex-biased ratios in some years. However, sex-biased ratios may be tied to one or more underlying influences including adult quality and environmental conditions.