Similarity in nest defense intensity in Canada goose pairs

Abstract

Individuals consistently differ in their behavior, and such personality differences are often linked to fitness. For biparental care species, the behavior of both parents can impact reproductive success. Behavioral similarity within pairs has been shown to provide selective advantages for many species. In this study, we tested for behavioral similarity in 129 pairs of nesting Canada geese (Branta canadensis) with respect to nest defense behavior, an individually consistent trait. We used a bivariate mixed model to provide unbiased estimates of correlations between partners’ traits. We also tested for the effect of behavioral similarity between mates on reproductive success and predicted greater success for positively assorted pairs. We found that over four consecutive years, pairs of Canada geese were formed of individuals showing similar nest defense intensities. Assortment between mates may result both from personality-dependent non-random mate choice and from behavioral adjustments after pairing that are maintained in the long term. However, behavioral adjustment to a shared environment, among and within breeding seasons, had negligible effects on the covariation between partners’ traits. We also found that similarity in nest defense intensity did not result in higher reproductive success. The factors at the origin of the evolution of long-term behavioral similarity based on nest defense in Canada geese pairs remain to be identified. Individual consistency in behavioral traits has been demonstrated for many animal species, and its importance in ecology and evolution is now accepted. The maintenance of personality traits in a population may in fact be explained by non-random mate choice like assortative mating, where paired individuals show similar phenotypes. We studied the nest defense behavior, a highly repeatable trait, of 129 Canada goose pairs during four consecutive years and found that paired individuals had similar personalities, suggesting personality-dependent mate choice or post-pairing adjustments maintained in the long term. Our findings also show that the phenotypic similarity between mated individuals is not always related to reproductive success and can possibly result from non-adaptive mechanisms.