In socially monogamous birds, pair‐bond duration varies across species, from single‐breeding associations to long‐lasting, multi‐year bonds. Studies of pair retention and divorce have focused on long‐lived and sedentary species rather than short‐lived and migratory species. Consequently, the fitness consequences of divorce or pair retention in the latter groups remain unclear. Here, we used a long‐term (1987–2023) and individual‐based dataset to investigate the reproductive consequences of pair retention and divorce in the European Pied Flycatcher Ficedula hypoleuca , a short‐lived, long‐distance migratory passerine. First, we described overall patterns of pair retention, defined as individuals pairing with the same partner across two consecutive breeding seasons, and divorce, defined as individuals switching partners between seasons despite spatial and temporal overlap with their previous mate. Then we tested whether reproductive parameters (laying date, clutch size and number of fledglings) differed between individuals that retained the same partner and those that divorce. Specifically, we compared the reproductive output of breeding pairs between the season before ( t ) and after ( t + 1) a pair retention or divorce event. Pair retention rates were lower (3.52% of breeding events) than divorce rates (4.7%), and both remained stable over the study period. Pair‐bond duration did not explain variation in laying date or clutch size. However, after accounting for confounding factors (e.g. age and breeding dispersal), divorce was associated with an increase in the number of fledglings in the year following separation for both males and females, supporting a direct influence of pairing status on reproductive performance. The opposite was true for faithful individuals, which showed higher success in their first breeding together relative to divorced individuals, but reduced reproductive performance in the second year. These findings, including the contrasting reproductive trajectories associated with pair retention and divorce, highlight the complex dynamics underlying pair‐bond stability in short‐lived migratory birds and emphasize the need to investigate its long‐term adaptive significance.
Rodríguez‐Solís et al. (Wed,) studied this question.