An experimental study examining the anti-predator behaviour of Sabine’s gulls (Xema sabini) during breeding

Anti-predatory behaviour is widespread among a broad range of animal taxa, including birds. Nest defence is not without risk, however, and parent birds face a trade-off between the survival of their offspring and the risk of injury or mortality to themselves. This study focused on the anti-predator behaviour of the Sabine’s gull (Xema sabini), a ground-nesting, Arctic breeder. Specifically, we quantified the gulls’ behavioural response towards natural predators, a human intruder, experimental predator decoys, and a non-predatory decoy. Neither the distance at which nesting Sabine’s gulls first reacted to natural predators, nor the relative intensity of their response, differed with incubation stage or predator type. However, response behaviour was highly variable among pairs. In response to decoys, Sabine’s gulls responded strongly towards predatory species, compared with a non-predatory species. The distance at which they first swooped at a human intruder was also variable, and there was no seasonal trend. Sabine’s gulls were often joined in nest defence by conspecifics, Arctic terns, and shorebirds nesting nearby, although the number of conspecifics involved in attacks was not related to the proximity of neighbouring nests.