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Japan NPO publishes first academic finding that some Asian black bears seem to kill cubs

A still image of male Asian black bear Akuosu, left, fighting with female bear Miroku is seen in this image provided by Picchio Wildlife Research Center.

NAGANO -- Is a bear cub's mortal enemy an adult male bear? Picchio Wildlife Research Center (Picchio), a nonprofit organization in the central Japan prefecture of Nagano that has engaged in conservation work on bears for over 20 years, says it has confirmed a case in which a mature male Asian black bear seems to have killed cubs.

    The results of the research carried out with Tokyo's Nippon Veterinary and Life Science University have been published in the online version of Ursus, an academic journal from the International Association for Bear Research and Management based in the United States.

    It appears to be the first time an Asian black bear has been academically confirmed to have killed a cub. Picchio hopes that the results of the latest work can serve as a starting point for developments in further research.

    Between April 1 and May 11, 2016, Picchio set up sensor cameras in a bear's winter den in a forest in the prefectural town of Karuizawa. The cameras then took still images of the female bear Miroku, her young and other animals.

    Among the images taken May 6 were some of a male Asian black bear, Akuosu, who appeared in front of the den. The pictures show him and Miroku engaged in a vicious altercation. After that, Akuosu was photographed leaving the den with the incapacitated bear cubs in his jaws. While Miroku's corpse was later found a short distance from the den, the cubs' bodies were not. Additionally, it wasn't possible to confirm if Akuosu and the cubs were father and children.

    Hiroo Tamatani, a member of the nonprofit organization Picchio Wildlife Research Center who engaged in the research on Asian black bears, is seen in the town of Karuizawa, Nagano Prefecture, on Nov. 4, 2021. (Mainichi/Mari Sakane)

    Hiroo Tamatani, head of wild animals at Picchio, indicated he didn't think this was an isolated case, saying: "We've seen a number of cases in which we've followed female bears who have given birth and who we've put transmitters on, and found them dead. It's said that traditional mountain hunters and bears kill bear cubs."

    Two theories reportedly exist regarding bears killing cubs. One is that females taking care of their young don't go into heat, and male bears kill the cubs to incite females into rutting and taking care of their own descendants. The second is that they kill and eat the cubs for sustenance.

    Miroku died within 24 hours of her cubs being taken away, a very short period for her to be able to become sexually active again and mate. This means the first theory can't be proven. Additionally, the cubs' corpses could not be found, meaning it's not certain whether they were consumed for their nutrition. Picchio says it intends to continue its investigations to shed light on the motivations behind cub killing.

    Chiho Yanagihara, a member of Picchio who was involved in the research, said: "We didn't do this with a view that bears are frightening creatures so of course they kill their young, but from a sense that we hoped we might be able to understand scientifically their circumstances as they occur in nature."

    (Japanese original by Mari Sakane, Nagano Bureau)

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