Earlier this month, zookeepers put Tsuyoshi under anesthesia to get to the bottom of the matter. That's when they made their discovery: Tsuyoshi is a female.
Still, the Kushiro zoo plans to keep Tsuyoshi because he -- or rather, she -- has become immensely popular with visitors.
"I have rather mixed feelings, given the need for breeding, but Tsuyoshi is an idol for Kushiro," Yoshio Yamaguchi, head of the Kushiro zoo, told Japan's Kyodo news agency.
Since the discovery was made, Tsuyoshi's "brother" was also found to be female. Link
(image credit: Kushiro Zoo)