February 27th is "International Polar Bear Bear Day." It was established in 2005 to raise awareness of the plight of Polar Bear, which are said to be endangered due to the effects of global warming, which is causing Arctic ice to shrink and depriving them of hunting grounds.

In conjunction with International Polar Bear Day, we will be presenting a two-part series on the efforts being made at Ueno Zoo to breed Polar Bear.

Ueno Zoo has breeding records for polar bears in 1917, 1918, and 1958, but none of the offspring have survived to adulthood. Because it is difficult for a single zoo to breed Polar Bear and maintain their exhibits, zoos throughout Japan are currently cooperating on breeding efforts.

Currently, our Polar Bear houses two polar bears: "Ikoro" (male, 14 years old), born at Sapporo Maruyama Zoo, and "Dea" (female, 14 years old), born at Fasano Safari Park in Italy. Because Dea, born in Italy, is of a different bloodline than Polar Bear that have been kept in Japan until now, breeding is hoped for in order to maintain the genetic diversity of Polar Bear in Japan. Ikoro, who came to our zoo in 2015, was chosen as her mate.

Polar Bear typically reproduce by mating during the estrus period (the time when females are receptive to mating partners) from winter to spring. At our zoo, we manage males and females separately, just like in the Polar Bear, and only allow them to live together when the females are in estrus.

To predict Dea's estrus period, our zoo measures changes in her blood sex hormones through regular blood tests. Additionally, as Dea's estrus period approaches, Ikoro begins to meticulously sniff Dea's feces and urine, and becomes excited, snorting at Dea through the fence. We use these changes in Ikoro's behavior as a criterion for deciding whether to begin cohabitation. However, simply cohabiting during estrus doesn't guarantee mating. In the next article, we will provide a detailed account of Ikoro and Dea's cohabitation so far.


Ikoro (left) and Dea (right), who live together.
[Ueno Zoo East Garden Animal Care and Exhibit Section]

◎Related News
・ Polar Bear "Dea" and "Ikoro" begin living together for the first time in preparation for breeding. (April 7, 2016)

(February 26, 2023)