Social scavenging by wintering striated caracaras (Phalcoboenus australis) in the Falkland Islands

Abstract

Abstract: 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. Significance statement: Currently ranked as Near Threatened by BirdLife International, the remote and restricted range of the striated caracara (Phalcoboenus australis) has made it a difficult study subject, though conservation concerns show it warrants deeper research. A social scavenging falconid of the Falkland Islands, striated caracaras have been persecuted as livestock pests since the 1800s, but their reliance on human settlements as winter foraging grounds makes them an ideal species with which to examine social scavenging behavior. This study was undertaken to investigate group feeding at carcasses by striated caracaras in austral winter, and to better understand the social function of their vocalizations. Furthering our knowledge of avian vocalizations is essential to certain wildlife management strategies, and empirically testing the effects of playbacks on target species is a crucial prior step to the use of any bio-acoustic tool.