Reproduction is affected by individual breeding experience but not pair longevity in a socially monogamous bird

In socially monogamous animals, maintaining stable mating pairs across years has been hypothesized to result in increased reproductive success. However, previous individual breeding experience may independently affect reproductive success, regardless of pair stability. We examined associations between pair composition based on previous breeding experience, pair longevity, and reproduction in socially monogamous mountain chickadees, Poecile gambeli, in the Sierra Nevada. There were no significant differences in any reproductive parameters between pairs of experienced breeders that had bred together in previous years and those that were newly formed. Pairs in which both partners were experienced had heavier nestlings than both first-year breeders and mixed experienced-inexperienced pairs. Experienced females started laying eggs earlier and laid larger clutches regardless of their social mate's previous breeding experience. As all experienced birds were older than inexperienced breeders, it remains possible that observed differences between these groups were due to age rather than breeding experience. Overall, our data did not support the hypothesis that pair longevity drives reproductive investment. Significance statement We showed that pair longevity in birds with previous experience had no significant association with any reproductive parameters. Instead, we detected that individual-level characteristics related to either previous breeding experience or age (first-year breeders vs. older, experienced breeders) were associated with earlier breeding, larger clutch size, and heavier nestlings. While it remains unclear whether age, breeding experience, or both influence the observed differences in reproductive investment, our results do suggest that pair longevity may not be a critical determinant of reproductive investment in a relatively short-lived, socially monogamous species.

Automated summary

In socially monogamous mountain chickadees, pair longevity did not have a significant impact on reproductive success, with individual-level characteristics such as breeding experience or age playing a more prominent role in influencing breeding behavior and outcomes.