Patterns and ecological predictors of age-related performance in female North American barn swallows, Hirundo rustica erythrogaster
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Life history theory describes the optimization of important trade-offs within an individual’s lifetime and predicts that an individual’s reproductive performance (RP) will improve up until a point of senescence. Despite abundant evidence for this pattern, relatively few studies consider the mechanisms associated with age-related improvements in RP. In this study, we aimed to describe patterns of age-related RP (seasonal fledgling production) in female North American barn swallows (Hirundo rustica erythrogaster) using a longitudinal data set to test multiple hypotheses about the social, morphological, and ecological factors underlying this prominent life history pattern. To address these objectives, we used generalized linear mixed models in a three-step series of analyses in which we assessed (1) patterns of female age-related RP; (2) the influence of age on changes in social, morphological, and ecological factors; and (3) whether the changes in RP were concomitant with changes in these factors. We found that (1) females showed patterns of age-related reproduction, in which performance increased in the first 2 years of breeding and decreased thereafter, (2) female tail streamer length increased and the extent of breast coloration increased then decreased significantly with age, and (3) changes in morphological traits did not covary with changes in reproductive performance over time. Our within-individual results highlight the importance of considering explicit links between morphology and reproductive performance that are not easily captured by population-level analyses.
KeywordsAvian Generalized linear models Life history Longitudinal analyses Reproductive performance Social and ecological factors
We acknowledge members of the Safran Lab at the University of Colorado, Boulder, for their comments and ideas throughout manuscript development as well as the field assistants that made collection of the data possible each summer: Matthew Wilkins, Conner Fitzhugh, Andrew Flynn, Maren Vitousek, Alexander Oesterle, Kate Gloeckner, Hayley Biddle, Tessa Warner, Stephen Alderfer, Audrey Tobin, and Ian Harold. We also acknowledge the Nevada Genomics Center for fragment analysis services. RJB was funded by the University of Colorado Boulder and Phi Beta Kappa. JKH and BRJ were funded by the University of Colorado Boulder Graduate School and the Ecology and Evolutionary Biology Department. RJS was supported by the National Science Foundation (IOS 0717421 and DEB-CAREER 1149942) and the University of Colorado.
The work done for this study has been approved by the University of Colorado’s IACUC (permit no. 1004.01), the Colorado Division of Wildlife, and the United States Federal Bird-Banding lab.
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