Earlier this week a 20-year-old female polar bear at the Detroit Zoo was killed by another bear while attempting to breed.

20-year-old Anana died when 16-year-old male Nuka was attempting to breed her. It was the first killing of an animal by another animal since 1988. So what went wrong? That's what experts are trying to figure out as it was a complete shock to everyone.

Nuka has been at the Detroit Zoo since 2011 and has lived and bred with several other female bears without incident. As a matter of fact, the recent birth of twin cubs, fathered by Nuka is proof of that.

Anana had only been at the Detroit Zoo a little over a year and was introduced to Nuka back in March.

According to a press release from the Detroit Zoo, after being apart for several months, Nuka and Anana were re-introduced last week as part of the Association of Zoos & Aquariums (AZA) Polar Bear Species Survival Plan, a cooperative population management and conservation program that helps ensure the sustainability of healthy captive animal populations.

Detroit Zoological Society Chief Life Sciences Officer Scott Carter:

This was completely unexpected and the Detroit Zoo staff is devastated by the loss of Anana in this sudden and tragic event.

I'm not sure what happens after a deadly attack like this. Does Nuka continue living there? I would like to think so since it was an isolated case and it's only in their nature to behave like this.

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