A Japanese zoo has abandoned its four-year attempt to get two hyenas to mate after realising both animals are male.
Maruyama Zoo, in Sapporo, said they were told Kami and Kamutori were a "male and female couple" by the South Korean zoo which sold them the spotted hyenas in 2010.
According to AFP, the zoo released a statement saying: "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.
"We have determined that the two animals are both male after conducting ultrasound imaging and hormone tests on them under anaesthesia."
ITV News reports that the zoo said "the external genitalia of the male and female are similar" which makes identifying their sex "very difficult".
The zoo will now find a female to breed with Kami or Kamutori.
The Civil Aviation Authority requested that pilots avoid flying in the area to reduce noise.
Tian Tian was artificially inseminated in April.
Zookeepers wanted to give the giant panda her best chance by asked pilots not to fly in the area.
It was reported in September that Tian Tian was no longer pregnant after losing her baby.
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