Professor Université du Québec à Rimouski Rimouski, Quebec, Canada
Background/Question/Methods
Global and rapid changes have occurred in the marine environment during the last decades. Facing prey depletion, many seabirds’ populations record decreased productivity. At the individual level, partner change (divorce) has been proposed to be an adaptive behavioral strategy in socially monogamous species to increase fitness, as a response to poor conditions and low breeding success. Since 2008, we monitored a population of gannets (Morus bassanus) nesting on Bonaventure Island (Quebec, Canada) and observed 809 individuals from 704 pairs between 2009 and 2019. In accordance with this hypothesis, individuals that divorced do so following a reproductive failure, and they increase their annual breeding success one year following the divorce. However, there is a great deal of inter-individual variability in the propensity to change partners in the population. To explain this variability, we investigated the individual’s characteristics influencing the decision-making process related to divorce as age, pair composition, and social lability (using the framework of social network analysis). Thus, the objective of this study was to compare the characteristics of individuals that divorce with those that retain their partners and to evaluate the impact on individual fitness.
Results/Conclusions
We found that gannets that changed partners tend to be slightly younger and pairs with younger individuals were more inclined to divorce. In contrast, pairs composed of old males and females had a durable pair-bond. On average, there were 2.2 ± 0.1 years between both partners. But when gannets divorced, the age difference increased by almost one year between mates in a new pair of divorced birds suggesting the prospecting of a more experienced partner. Pluriannual reproductive success increased with pair duration but only for the first four years. At the social-environmental level, we found that more socially labile individuals divorced more, suggesting the highest number of interindividual connections at the nesting colony tends to be a key to prospect for a better-quality partner. However, more socially labile individuals had lower pluriannual reproductive success. Overall, in a changing environment with low food resources, our results suggest that while it is preferable in the short term for the youngest and most socially labile gannets to change partners after breeding failure to increase their breeding success, this strategy does not appear to be beneficial in the long term as individuals in longer-lasting pairs tend to achieve better fitness.
