Low mate and nest fidelity in a declining population of Antarctic Shags at Harmony Point, South Shetland Islands, Antarctica

Mate and nest‐site fidelity are widespread breeding behaviours in long‐lived seabirds and may be shaped by previous breeding success. The ‘success–stay, failure–leave’ strategy predicts that individuals are more likely to retain their mate and/or nesting site following successful reproduction, whereas breeding failure may increase the likelihood of changing mates or nesting sites. We investigated mate and nest‐site fidelity, and their relationships with previous breeding success in an individually marked population of the Antarctic Shag Leucocarbo bransfieldensis at Harmony Point, Nelson Island (South Shetland Islands, Antarctica), using individual and pair records collected between the 2000/2001 and 2005/2006 breeding seasons. Overall, 47.1% of pairs remained together, although some individuals skipped one or more breeding seasons. Recapture probability was lower in females than in males, whereas males reused nests more frequently (76.9%) than females (23.9%). Mate fidelity was strongly associated with nest fidelity, but no association was observed with breeding success in the previous season. Furthermore, breeding success did not differ significantly between newly formed and established pairs. These results do not support the ‘success–stay, failure–leave’ strategy, suggesting that previous breeding success alone does not explain variation in mate and nest‐site fidelity. Our findings provide new insights into breeding behaviour, and mate and nest fidelity, in a poorly studied Antarctic seabird.