ROYAL OAK, Mich. (AP/WIVB) — Officials say a male polar bear killed a 20-year-old female polar bear at the Detroit Zoo when he attempted to mate.

The zoo says 16-year-old Nuka killed Anana on Monday after being apart for several months. Scott Carter, the zoo’s life sciences officer, says the death was “completely unexpected.”

The zoo says Nuka has lived at the zoo since 2011 and bred with other female bears without harmful behavior.

Anana arrived at the zoo in suburban Detroit in January 2020 and was introduced to Nuka a few months later.

The zoo says the mating program “is vital to sustaining this endangered species.”

Anana previously lived at the Buffalo Zoo for many years, and gave birth to Luna, a popular polar bear who still calls Buffalo home.

The Buffalo Zoo released a statement on Anana’s death:

“We are incredibly sad to hear of Anana’s passing. She was a beloved member of the Buffalo Zoo family for many years and the mother to our own Luna. She will be greatly missed. Our hearts also go out to our colleagues at the Detroit Zoo, who are dealing with this tragic situation.”

The Buffalo Zoo