cannibalism in the animal kingdom is not rare -- 3/21/17

21 Mar 2017

cannibalism in the animal kingdom is not rare -- 3/21/17

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Today's selection -- from Cannibalism: A Perfectly Natural History by Bill Schutt. Cannibalism in the animal kingdom is not rare:

"Cannibalism has been recorded in at least 14 species of carnivores. In pumas (Puma concolor), lynx (Lynx lynx), leopards (Panthera pardus), and sea lions (Phocarctos hookeri), it appears to occur for many of the usual reasons, including stress (due to lack of food), elimination of rivals, and increased mating opportunities.

"Heterocannibalism, in this case, eating the cubs that another male sired, is clearly a reproductive strategy in male lions (Panthera leo) after taking over a pride. Through the practice of infanticide, the incoming males terminate the maternal investment in unrelated cubs. A lioness with cubs will not come into heat for a year and a half after giving birth, but similar to what has been observed in other mammals, a lioness that loses her cubs becomes sexually receptive almost immediately. ...

"According to wildlife biologist Mitchell Taylor, 'Polar bears will readily eat other polar bears when they can do so without excessive risk of injury.' In fact, males of most North American bear species will kill and eat conspecific cubs pretty much whenever they can get their paws on them. Researchers believe that infanticide during the breeding season may provide males with 'a reproductive opportunity as well as a nutritional reward' since like the previously described lionesses, female polar bears will come into estrus more quickly if their offspring have been killed. Because of this, cannibalism has been, and continues to be, one of the greatest contributors to bear cub mortality, especially just after leaving the maternity den. The threat from adult males is one of the key reasons that mother bears are so protective of their cubs and also explains why females give males such a wide berth when selecting maternity den sites. ...

"[In] 2006 [there were] three [reported] incidents of cannibalism by polar bears in the southern Beaufort Sea, which occurred during a two-and-a-half-month period. Two of the incidents involved the death and partial consumption of adult female bears. In one, the female's body was found inside a maternity den that collapsed during an attack by a predatory male bear. In the second case, the female polar bear was killed on the sea ice, presumably not long after emerging from its den with a cub. In the third case, a one-year-old male was killed and partially consumed by an adult male.

" [There were associated reports that the cause of this cannibalism] was global warming [which] had reduced the Arctic sea ice, thus resulting in shorter hunting seasons for the bears and fewer seal kills. As a consequence, the stressed-out bears were starving and resorting to cannibalism in order to survive. The problem with most of these stories was that the authors left out a rather important fact -- and it was one that researchers have known for decades ... that cannibalism in polar bears was already known to be a naturally occurring event, with the first published report surfacing in 1897."