Observations of intraspecific killing, cannibalism, and aggressive behavior among polar bears ( Ursus maritimus ) in the
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SHORT NOTE
Observations of intraspecific killing, cannibalism, and aggressive behavior among polar bears (Ursus maritimus) in the eastern Barents Sea and the Kara Sea E. A. Ivanov1 · I. A. Mizin2 · A. G. Kirilov2 · N. G. Platonov1 · I. N. Mordvintsev1 · S. V. Naidenko1 · V. V. Rozhnov1 Received: 19 May 2020 / Revised: 4 November 2020 / Accepted: 7 November 2020 / Published online: 18 November 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The ability of the polar bear (U. maritimus) to kill and consume conspecifics is accepted, but the reasons behind this behavior and its prevalence remain unclear. Here, we report 14 cases of intraspecific killing, cannibalism, and aggressive behaviors among polar bears observed in seven instances in the Barents Sea and the Kara Sea on Frans-Josef Land, Novaya Zemlya, and Vize Island. All but one of the observations were made on land during the ice-free season. Perpetrators, when observable, were mostly thin. The hunger resulting from a failure to gain fat reserves in spring appears to motivate perpetrators, while bear aggregation on islands could facilitate successful intraspecific killing. Surprisingly, cases of intraspecific killing were observed even in years when sea-ice conditions in the previous spring were relatively good. In one case, the killing of a cub of the year in the spring by a large, fat male could hardly be explained by nutritional demands. This could be a case of sexually selected infanticide, as the killing of cubs during the mating season increases the male’s opportunity to breed. Keywords Polar bear · Barents Sea · Kara Sea · Intraspecific killing · Cannibalism · Infanticide
Introduction Since the late nineteenth century, numerous cases of intraspecific killing and cannibalism among polar bears (U. maritimus) have been reported (Nansen 1897; Urvantsev 1935; Uspenski and Kitchinski 1972; Lunn and Stenhouse 1985; Taylor et al. 1985; Derocher and Wiig 1999; Dyck and Daley 2002; Amstrup et al. 2006; Stone and Derocher 2007; Stirling et al. 2008a; Stirling and Ross 2011), but the reasons and significance of this behavior remain unclear. Several mechanisms that increase evolutionary fitness by killing conspecifics are recognized, and theoretical implications are well developed (Hrdy 1979; Ebensperger 1998). However, our knowledge on reproductive behavior, dispersion, and several other biological and ecological parameters of polar bear populations is still incomplete. As polar bears * E. A. Ivanov [email protected] 1
A.N. Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow, Russia
Russian Arctic National Park, Arkhangelsk, Russia
2
spend most of their lives in remote areas, it is difficult to precisely observe their behavior. In most cases, we rely on anecdotal, incomplete, or indirect evidence. Females with cubs avoid adult males and areas where the probability of interaction is high, both on land and on ice (Derocher and Stirling 1990a; Ferguson et al. 1997; Pilfold et al. 2014); it c
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