Permanent and temporary mate switching in a long-lived seabird: insights from a 64-year study

In long-lived socially monogamous animals, pair bonds play a crucial role in breeding success. In many predominantly socially monogamous animals, however, there is often some degree of mate switching. Mate switching may represent an opportunity to acquire a higher-quality partner or breeding site following breeding failure. Using a 64-year data set, we investigated the dynamics of mate switching in Leach's storm-petrels, Hydrobates leucorhous . We observed that, on average, 4.3% of pairs permanently switched mates each year (i.e. permanent mate switch), with an increasing rate in recent years. Following a permanent mate switch, one member of the original pair improved its hatching success, while the other experienced a significant decline. These data support the better mate hypothesis, where individuals switch partners to obtain a higher-quality mate, rather than the better fit hypothesis, which predicts switching to improve pair compatibility. A small proportion (1.1% annual average) of pairs switched mates but reunited in a later year (i.e. temporary mate switch). As expected from previous studies, breeding failure was a significant predictor of permanent mate switching. But temporary mate switching was unrelated to breeding failure, suggesting these two kinds of mate switching are caused by different decision-making processes. Of the environmental variables tested, global mean temperature (GMT), Atlantic Multidecadal Oscillation (AMO) and North Atlantic Oscillation (NAO), only rising GMT was associated with increases in both temporary and permanent mate-switching rates, raising the possibility that climate change, together with other ecological pressures, may further destabilize population dynamics in this declining seabird species.