Rhinoceros Auklet pair‐mates migrate independently but synchronize their foraging activity during the pre‐laying period

Pair bonds are considered important for successful breeding in monogamous birds but their maintenance may be challenging for migratory species, as mates can be separated for months during the non‐breeding period. To investigate whether mates of monogamous migratory seabirds stay together throughout the non‐breeding period and how and when they start synchronizing their activity before breeding, we tracked seven pairs and 22 individuals of Rhinoceros Auklets Cerorhinca monocerata with geolocators and saltwater immersion loggers. Mates migrated across similar areas during the non‐breeding period but with a sustained temporal shift, putting them an average of 377 km apart and resulting in an average difference of return date at the colony of 5.6 days, with no sex biases. These values did not differ significantly from those between ‘pairs’ of randomly selected, non‐mated birds. Mates showed synchronized on‐water/in‐air at‐sea activities once both birds returned and spent the first night together at the colony. The synchronization of activities was highest on the day following the nights when both mates visited the colony, and decreased with elapsed time. Mates then left the colony together for a pre‐laying exodus of 8–9 days and males returned 2–4 days earlier than females before incubation started. Mates kept synchronizing at‐sea activity during the early part of the exodus. We interpret this as the mates staying together at sea during the pre‐laying period, increasing the males’ chances of copulation at sea. The patterns of mate association observed in Rhinoceros Auklets contrast with those of the Procellariiformes, presumably reflecting differences in the place and timing of copulation.