February 27th is "International Polar Bear Bear Day." Following on from last time, we will introduce the efforts being made at Ueno Zoo to breed Polar Bear.

In 2016, the year after "Ikoro" (male) arrived at the zoo, we attempted to have Ikoro and "Dea" (female) live together for the first time.

Immediately after they first started living together, the two dogs were wary of each other, but gradually they grew closer, and by the end of that year, they had developed such a good relationship that they were playing together in the pool. When Dea's estrus reached its peak, Ikoro would become excited, snorting and chasing after her. However, Dea was quicker to escape, so Ikoro couldn't get close to her and could only maintain a certain distance, wandering around nearby.

Apparently, similar behavior is observed initially in pairs of aviary lizards at other zoos and aquariums that have successfully bred. In cases where mating is successful, the male gradually closes the distance and makes contact with the female, and the female accepts this, leading to mating. It seemed that Ikoro and Dea, who have neither of them had mated before, might need a little more time.


"Dea" (top) is running away, while "Ikoro" (bottom) maintains a certain distance.
It was on December 26, 2018, that Ikoro first mounted Dea (the male mounts the female and assumes a mating position). The mounting position was poor, and it didn't look like the mating was successful, but it was a huge step forward. Mounting was observed during their cohabitation in the following years, suggesting that Dea may have become more tolerant of Ikoro.

However, given that Dea has not become pregnant so far, and that her mounting position appears insufficient compared to the mountings of pairs in other zoos that have successfully mated, it is believed that mating did not occur. Mounting was observed in January this year. However, it is difficult to determine whether mating was successful by visual inspection alone, and it is unclear whether mating was successful until Dea showed signs of giving birth afterward.


"Ikoro" (right) mounts "Dea" (left).
We would like to continue breeding Ikoro and Dea together indefinitely, but in order to ensure that we do not miss their breeding age, we need to consider all possible methods. Since the compatibility of the pair is also important for breeding, we may need to cooperate with other zoos and aquariums to swap males and females or perform artificial insemination.

For the future of Polar Bear in Japanese zoos, we will continue to work energetically on breeding with a broad perspective, and we hope that one day you will be able to see Polar Bear cub at Ueno Zoo. Furthermore, through our polar Polar Bear, we hope that we can all work together to protect wild Polar Bear by taking steps to reduce CO2 emissions and actively using environmentally friendly products. We hope that today, International Polar Bear Day, will be a day for everyone to think about Polar Bear, even just a little.

[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 27, 2023)