Zookeepers in Japan have abandoned an attempt to have two spotted hyenas mate and reproduce as both turned out to be male.
The Maruyama Zoo in Sapporo, northern Japan, said in a statement this week that it was gifted the animals as a "male and female couple" in October 2010 from a zoo in the South Korean twin city of Daejon.
"We have attempted to house them together for breeding many times but they often fought against each other and never engaged themselves in breeding behaviour," the statement said.
Kami, the supposedly female hyena now five years old, has shown no estrus symptoms after reaching sexual maturity, prompting the zoo to put it and its six-year-old partner Kamutori to sex tests.
"We have determined that the two animals are both male after conducting ultrasound imaging and hormone tests on them under anaesthesia," the statement said.
The zoo explained that it is "extremely difficult" to determine the sex of a spotted hyena from the appearance of its external genitalia.
"We still plan to obtain a female spotted hyena for breeding with either Kami or Kamutori," the statement said.