Times and partners are a-changin’: relationships between declining food abundance, breeding success, and divorce in a monogamous seabird species

Seabirds exhibit considerable adjustment capacity to cope with environmental changes during the breeding season and to maximize lifetime reproductive output. For example, divorce has been proposed to be an adaptive behavioral strategy in social monogamous species, as a response to poor conditions and low breeding success. Here, we studied divorce at the population and individual levels in northern gannets (Morus bassanus, hereafter gannets) nesting on Bonaventure island (Quebec, Canada). At the population level, we used Granger’s method for detecting and quantifying temporal causality between time series (from 2009 to 2019) of divorce rate and breeding success of gannets (n = 809) and we evaluated the relationship between breeding success and biomass of their two principal prey (Atlantic mackerel, Scomber scombrus, and Atlantic herring, Clupea harengus). Our results indicated that breeding success is mainly influenced by the spawning-stock biomass of Atlantic mackerel, and a decrease in breeding success is followed by an increase in divorce rate with a 1-year lag. However, the effect of the interaction between breeding success and year on the proportion of individuals that divorced showed significant inter-annual variation. At the individual level, our results support the adaptive strategy hypothesis of divorce. Indeed, gannets that changed partners did so following a reproductive failure, and there was an increase in breeding success 1 year following the divorce. Being central place foragers, opportunities for dispersal and adaptation are often limited for breeding seabirds in a context of low food abundance. We suggest that behavioral flexibility expressed as divorce would be an efficient short-term strategy for maintaining reproductive performance.