COS 164-4 - Should I stay or should I go? The cost of divorce in the thick-billed murre

Background/Question/Methods

Many species are monogamous, meaning that choosing the right partner may have an important effect on reproductive success. Pair-bond duration and increased pair familiarity often enhances reproductive success. A divorce between mates can occur as (i) an adaptative behavioral strategy for an individual with a suboptimal partner, (ii) a random event driven by the mistiming of mate arrival as individuals or (iii) an opportunistic behavioural strategy occurring in years of high mortality when many new partners are available. Divorce occurs when both partners are still alive and where subsequent breeding attempts, of at least one bird, are with another partner. The thick-billed murre (Uria lomvia) is a colonial long-lived seabird species considerable bi-parental care. As the species breeds in the Arctic, birds have a short breeding season, and this constraint should add a major cost to divorce, if divorce requires time to create mate compatibility. Using monitoring data collected from 24 years at the Coats Island murre colony (Nunavut), we aim to access the factors that influence the probability of divorce and the impacts and costs of partner change.

Results/Conclusions

We found a divorce rate of 9% for our 372 murre pairs from 1991-2010 and 2017-2019. Divorce rate decreased with breeding experience, nest site quality, and successful fledging. Divorced birds did not get assess to a better quality partner or nest site. We did not find an effect of population-wide survival rate on the probability of divorce, contrary to what was found in a congener at lower latitudes. Nonetheless, fledging success was higher for faithful birds compared to divorced birds, showing the importance of mate fidelity in this species. In conclusion, for an Arctic species with a short breeding season, divorce rate was low and long-term partnerships beneficial in this long-lived species, but when divorce occurred it tended to increase fledging success of both partners.