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1 December 2012 Effect of Nestling Sex Ratio on the Provisioning Behavior of Sialia sialis (Eastern Bluebird)
Barbara E. Kieffer, Gary Ritchison
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To maximize reproductive success, parents may differentially invest in sons and daughters, i.e., sex-biased parental investment. Preferential provisioning behavior has been reported in one population of Sialia sialis (Eastern Bluebird) and attributed to local resource competition. We studied the provisioning behavior of Eastern Bluebirds in Madison County, KY in 2004. We experimentally manipulated brood sex ratios in 24 bluebird nests, creating female-biased (n = 8), male-biased (n = 5), and control (n = 11) nests. Following manipulation, nests were videotaped to record adult provisioning behavior. Brood sex ratio had no effect on the provisioning behavior of either male or female Eastern Bluebirds. Similarly, we found no effect of brood sex ratio on the provisioning rates of either male or female bluebirds for control broods that naturally differed in number of male and female nestlings (n = 9; 5 male-biased and 4 female-biased). Our results contrast with those of a previous study that found that male Eastern Bluebirds fed nestling males less than nestling females, possibly because sons were more likely to compete with them for resources in the future. However, local resource competition seems unlikely because Eastern Bluebirds exhibit low rates of philopatry. Given these conflicting results, additional study is needed to determine if factors such as latitude, food availability, or availability of other resources might influence the provisioning behavior of male Eastern Bluebirds.

Barbara E. Kieffer and Gary Ritchison "Effect of Nestling Sex Ratio on the Provisioning Behavior of Sialia sialis (Eastern Bluebird)," Northeastern Naturalist 19(4), 685-690, (1 December 2012).
Published: 1 December 2012

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