Behavioural Syndromes, Partner Compatibility and Reproductive Performance in Steller's Jays

The concept of partner compatibility in monogamous animals implies that individuals may reproduce better when paired to a partner with similar traits than to a higher quality, but dissimilar individual. We investigated whether partner similarities in traits that are linked in a behavioural syndrome influence reproductive performance in a wild population of Stellers jays. In some years, pairs more similar in explorative tendencies and in willingness to take risks initiated nests earlier and were more likely to fledge offspring than dissimilar pairs. Benefits of behavioural similarity differed among breeding seasons, being most pronounced in a year with late breeding onset after a severe winter. Pairing patterns for behavioural traits also varied among years and traits, and assortative pairing of behaviourally similar partners was not only common overall, but was also correlated across the three explorative and risk-taking tendencies. Pair members with behavioural similarities may yield more compatible and complementary partnerships. Our results indicate that compatibility across a suite of behavioural traits (i.e. a behavioural syndrome) may be beneficial for assortative pairs and support the hypothesis that the combination of traits in behavioural syndromes in itself might be a target for selection.