Mate fidelity in a double-brooded urban passerine

Abstract

Every bird requires a mate to have a successful breeding attempt. After each brood, they are faced with the choice to stay with or separate from this mate. The choice to stay together is referred to as mate fidelity and can benefit the future reproductive success of the pairs who exhibit it. Despite these benefits, separation is still common in many populations of passerines, leading to the question of the costs of mate fidelity and under what circumstances these might outweigh the benefits. In this study, I examined the frequency of mate fidelity in a population of urban dwelling European Starlings (<i>Sturnus vulgaris</i>) over 15 years. Mate fidelity or subsequent separation events were then compared to average brood condition of each brood raised together to test if any correlation between them existed. Tests were run between the first and last brood raised by a faithful pair, and between the first brood from a faithful pair and the first and only brood raised by a pair that subsequently separated to determine if brood condition affected fidelity in the population. While mean brood condition followed the prediction that broods preceding fidelity would be higher in condition than those which preceded separation, the difference between the two categories was not statistically significant in either test. These findings still warrant investigation, as the difference in condition was noticeable, and sample sizes were small, so we may have lacked the statistical power to detect such influence. Brood condition could still influence the frequency of mate fidelity within this population along with other possibilities.