TOKYO — It was an auspicious sign, as the giant panda shimmied into a handstand and urinated upside-down against a tree.
Nearly four years had passed since Ri Ri, a 15-year-old male, last mated with his partner, Shin Shin, also 15, at Japan’s oldest zoo. But last November, Ri Ri began his courtship ritual (the acrobatics leave a wider scent) and Shin Shin was found to be nearing heat, raising hopes that the famously finicky animals were at last in the mood.
Early this month, Ueno Zoo in Tokyo announced that there were signs that Shin Shin was pregnant. Share prices for restaurants with outlets around the zoo soared. And then on Wednesday came the happy news: Shin Shin had given birth to not one cub, but two.
The twins, whose sex has not yet been determined, were born just after midnight an hour and a half apart, the zoo said. One weighed 124 grams, or nearly four and a half ounces, and the weight of the other was still unknown. They joined a sister, Xiang Xiang, who was born in 2017.
Yutaka Fukuda, the zoo’s director, called the twin births a joyful surprise.
“When the first one was born, I was relieved,” Mr. Fukuda said during a news conference on Wednesday morning. “When I received a report about the second one, I was shocked and extremely happy.”
A spokesman for the zoo, Naoya Ohashi, said that when pandas have twins, they usually raise only one of them, so the zookeepers are making sure that the mother breastfeeds one while the other stays in an incubator. They plan to swap the cubs out from time to time so that they both experience natural feeding.
Previously, five pandas — three male and two female — had been born at Ueno Zoo, which opened in 1882 on grounds once held by the imperial family and, with its surrounding park, is one of Tokyo’s most popular tourist destinations. This is the first time that twins have been born at the zoo.
In the 1980s, two pandas named Fei Fei and Huan Huan had three cubs through artificial insemination, although one of the babies died after just two days.
Shin Shin and Ri Ri arrived 10 years ago, and Shin Shin gave birth through natural conception for the first time in 2012. The cub died of pneumonia a few days later. Xiang Xiang, their daughter, is now 4.
Xiang Xiang had been scheduled to be repatriated to China after turning 2, but Japanese officials negotiated an extended stay. She was then set to be returned by May 31, but that has been delayed until Dec. 31 because of the pandemic.
Shin Shin and Ri Ri were supposed to return to China in February. But the Tokyo governor, Yuriko Koike, who feared that the zoo would be left with no pandas and deprived of a major draw for visitors, negotiated to lengthen their stay by five years. Ueno Zoo reopened earlier this month after a five-month closure related to the pandemic.
China’s practice of giving pandas to other countries is said to stretch back well over 1,000 years. Chinese state media has reported that historical records show that the Chinese empress Wu Zetian sent two pandas in the year 685 to Emperor Tenmu of Japan.
China first sent pandas to Ueno Zoo in 1972, as part of the country’s “panda diplomacy,” which had gained steam in the 1950s.
Today, China offers pandas to other nations only as 10-year loans, with all offspring considered to be Chinese property. There are about 1,800 giant pandas in the wild in China, as well as about 500 in captivity around the world.