Should I stay or should I go: factors influencing mate retention and divorce in a colonial seabird

Abstract

Divorce among serially monogamous birds can lead to increased reproductive success if an individual obtains a higher-quality mate or nest site, or it can lead to lower reproductive success due to lack of pair experience or reduced breeding opportunities. Identifying the drivers and consequences of mate retention and divorce are necessary then to understand population dynamics, particularly as animals may alter behaviours in response to climate-induced environmental changes. We used a 33-year data set from a declining Magellanic penguin, Spheniscus magellanicus, colony to identify drivers of mate retention and divorce and test whether the nature of those drivers differed between first-year and long-term pairs. In a pair's first year, breeding outcome was the most important predictor of whether mates would reunite: failure rates were high and 71% of first-year pairs divorced on the whole, but only 47% of pairs that fledged a chick divorced. For long-term pairs, both breeding outcome and between-season changes to nest quality were the most important predictors of whether a pair stayed together: pairs that had a chick hatch or fledge divorced at lower rates than those that failed at the egg stage, and pairs whose nest quality declined were more likely to divorce. We also examined the fitness consequences of divorce by comparing the rates at which females and males obtained new mates and fledged chicks in the following year. Although females were more likely than males to secure a new mate, both sexes experienced similarly increased reproductive success with their new mates compared to their old mates, showing that divorce is adaptive.