The Differential Reproductive Performance Of Female Tree Swallows, Tachycineta bicolor

Differential reproductive performance among age classes has been observed in many avian species. In general, older and experienced breeders exhibit a greater reproductive output than young and inexperienced breeders. Several hypotheses have been proposed to explain the difference in reproductive performance, including the Breeding Experience Hypothesis and the Age Hypothesis. In the present study, I tested for differences in reproductive performance between two age classes: young, first-time breeding females and older, experienced females in a population of tree swallows (Tachycineta bicolor) nesting in Elkhorn Slough, California. There were no significant differences in all aspects of incubation behavior measured. However, older females exhibited greater reproductive output than younger females due to earlier lay dates and larger clutch sizes. My results suggest that the reproductive performance of young female tree swallows is constrained by age rather than breeding experience