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.

中文翻译：

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巴伦支海东部和喀拉海北极熊（Ursus maritimus）的种内杀戮、同类相食和攻击行为的观察

北极熊（U. maritimus）杀死和食用同种动物的能力是被接受的，但这种行为背后的原因及其普遍性仍不清楚。在这里，我们报告了 14 例北极熊在巴伦支海和喀拉海的法兰斯约瑟夫地、新地岛和维兹岛中观察到的 14 例种内杀戮、同类相食和攻击行为。除一项观测外，所有观测都是在无冰季节在陆地上进行的。可以观察到的肇事者大多都很瘦。春季未能获得脂肪储备而导致的饥饿似乎会激励肇事者，而岛屿上的熊聚集可以促进成功的种内捕杀。令人惊讶的是，即使在前一个春天海冰条件相对较好的年份，也观察到了种内杀死的案例。在一种情况下，一只又大又肥的雄性在春天杀死了一只一年中的幼崽，这很难用营养需求来解释。这可能是性选择杀婴的案例，因为在交配季节杀死幼崽会增加雄性繁殖的机会。