Foraging behaviour and habitat use by brown skuas Stercorarius lonnbergi breeding at South Georgia

Top predators are critical to ecosystem function, exerting a stabilising effect on the food web. Brown skuas are opportunistic predators and scavengers. Although skuas are often the dominant land-based predator at seabird colonies, this is the first detailed study of their movements and activity during breeding. The study was carried out at Bird Island, South Georgia (54°00′S, 38°03′W), in the austral summer of 2011/2012 and included GPS data from 33 breeding adults tracked during the late incubation and early chick-rearing periods. Brown skuas spent on average more than 80 % of time in the territory, and it was extremely rare for both partners to leave the territory simultaneously. Much more time was spent foraging at the coast than in penguin colonies and, based on saltwater immersion data, adults never foraged at sea. None of the tracked birds appeared to specialise in catching small petrels at night. Fewer foraging trips were made per day, and hence, more time was spent in the territory, during incubation than chick-rearing. Despite the pronounced sexual size dimorphism, there were no effects of sex on territorial attendance, foraging time or habitat use. Skuas at Bird Island show higher territorial attendance and are less likely to leave the territory unattended than those breeding elsewhere, suggesting closer proximity to more diverse or abundant food resources than at other colonies. The results tie in with previous diet studies, indicating that brown skuas at this site feed mostly on seal placentae and carrion and that birds may rely on a broader range of food resources as the season progresses

vertebrate scavenging communities

A scavenger is an animal that feeds on the carcass or remains of any dead animal which it did not participate in its killing. Scavenging is pervasive across the animal kingdom and almost all predator species use carrion to a certain extent in both terrestrial and aquatic ecosystems. There is a group of animals, the obligate scavengers, which rely (almost) entirely on carrion. Among vertebrates, only birds have evolved into obligate scavengers, namely vultures, which suggests that the costs of adaptation to obligate scavenging are high. Obligate and facultative scavengers exhibit a wide array of adaptations to locate and exploit carrion across systems, including inexpensive locomotion to find the unpredictable carrion on savannas, caching carrion in cold tundra or chemotaxis in aquatic systems. Traditionally viewed as an opportunistic process, particularly for facultative scavengers, carrion consumption by vertebrates often follows complex and structured patterns and is crucial in maintaining the stability and structure of food webs.Peer reviewe