Social Scavenging by Wintering Striated Caracaras (Phalcoboenus australis) in the Falkland Islands

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Avian scavengers perform vital ecosystem services by removing waste and slowing disease, yet few details are known about the process of carcass depletion, or the role of social interactions among groups of scavengers. The striated caracara (Phalcoboenus australis) is a social scavenging falconid of the Falkland Islands, whose boldness and reliance on human settlements as winter foraging grounds make it an ideal species with which to closely examine carcass use over the entire period of a carcass’ availability. By providing and monitoring experimental carcasses, we estimated the mass of food consumed per individual during 5-min intervals and compared the rate of group formation in the presence and absence of conspecific vocalizations. We found (1) that food obtained per individual was greater toward the beginning of carcass availability, when competition was fierce; (2) that vocalizations, by birds at and approaching the carcass, preceded periods of faster group formation; and (3) that on average birds would approach a speaker playing conspecific calls more closely than one playing a control recording. Our observations add to those of social foraging in other scavengers, providing a study of carcass use and vocalization at these ephemeral resources.