Spatial segregation by sympatrically breeding Antarctic and Snow Petrels.

Abstract

Sympatrically breeding species may face intense competition for resources, which can lead to various forms of segregation to mitigate competitive pressures. Segregation of space or habitats is one possible strategy, particularly when species share similar diets and foraging behaviors. This study examines the differences in space and habitat use between Antarctic and Snow Petrels (Thalassoica antarctica and Pagodroma nivea) breeding at the Svarthamaren colony (Dronning Maud Land, Antarctica), by using fine-scale tracking data. We analyzed the characteristics of their foraging trips, estimated the foraging areas, and assessed the overlap between them. Additionally, we quantified their sea-ice use at foraging locations and compared them between the two species, with the prediction that Snow petrels were more associated to sea-ice than Antarctic Petrels. The results indicate that Antarctic Petrels traveled on average at faster speeds, covered greater distances, and for longer durations during incubation than Snow Petrels. During chick-rearing, however, Snow Petrels traveled further than Antarctic Petrels, the difference in speed remained the same. These two petrel species showed clear spatial segregation, during both incubation and chick-rearing, with their foraging areas overlapping by less than 20%. Antarctic Petrels generally traveled northeast of the colony while Snow Petrels traveled westwards and closer to the shore. As predicted, Snow Petrels were 45% less likely to use areas without sea-ice compared to Antarctic Petrels when foraging. This study provides valuable insights into the at-sea space use and habitat preferences of these relatively understudied species during the breeding season. It underscores the importance of segregation strategies for their coexistence and emphasizes their dependence on sea-ice, particularly for Snow Petrel, rendering them potentially vulnerable to the loss of sea-ice due to climate change.