In long-lived monogamous animals, pair bonds play a crucial role in breeding success. In many predominantly 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 dataset, 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. 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. Rising global mean temperatures (GMT) was associated with increases in both temporary and permanent mate switching rates, raising the possibility that ongoing climate change will destabilize future population dynamics in this declining seabird species.