MARTA TOGNETTI1, SIMONA SANVITO2, and FILIPPO GALIMBERTI2 1 Dipartimento di Scienze Naturali, Università degli Studi di Milano 2 Elephant Seal Research Group, Sea Lion Island, Falkland Islands SOCIALITY IN KILLER WHALES: THE ROLE OF RECRUITERS Killer whales are an apex predator species, with a worldwide distribution, a complex sociality and communication system, and advanced hunting techniques that let them prey on species of very different size and habits. Although killer whales were studied extensively in the northern hemisphere, knowledge about populations of the southern hemisphere is rather limited. We studied sociality of killer whales at Sea Lion Island (Falkland Islands; SLI hereafter) during two seasons (September 2013 to March 2015) for a total of more than 400 days spent in the field. We used a combination of photo-identification, surveys and observations from vantage points. We identified 31 killer whales, some of them observed the first time in 2004, using features of the saddle patch and the outline of the dorsal fin (DARWIN software). We assembled adjacency matrices of identified individuals, we calculated association indices, and we used social networks methodologies to visualize and quantify killer whales social structure. At SLI the basic social unit was the mother-calves group, that included a maximum of three calf generations. Mother-calves groups formed a hierarchical, matrilineal social structure. Males were quite irregular in their presence, association among themselves, and bond with other killer whales, although they were sometimes involved in social predation events. Killer whales were either regular visitors of SLI, spending an important share of their time close to the island, or occasional visitors appearing for just a very short time (few hours to few days). Different groups of occasional visitors were always observed together with a specific mother-calf pair (Lola and Ale), that had a high centrality in sociograms, and apparently acted as recruiter and social facilitator for the coming of new individuals. Group size and association patterns changed along each season, and between the two seasons, but the basic building blocks of the social structure remained the same The complex sociality observed at SLI was related to hunting tactics. At SLI, killer whales prey on two species of pinnipeds, the southern elephant seal and the southern sea lion. Predations were social events involving up to 13 individuals, lasted a long time in case of large seals (e.g., sub-adult males), and sometime involved the males, although actual killing was usually carried out by adult females. Social prey sharing was the norm.