Endangered Monkey at Philadelphia Zoo, Toi, Euthanized After Declining Health

Red-Shanked Douc langur
Nhon, a douc langur, eats as her newborn clings to her during an afternoon feeding session at the Singapore Zoo, on September 4, 2006. The last red-shanked douc langur living in a zoo in North America was euthanized Wednesday. Tim Chong/Reuters

A rare monkey, the last of its kind in a North American zoo, was euthanized at the Philadelphia Zoo on Wednesday after a decline in its health.

The 21-year-old monkey, Toi, was experiencing decreasing mobility and a change in normal behavior, WCAU reported. Toi was a red-shanked douc langur, a species that is considered critically endangered, according to the World Wide Fund for Nature.

The monkey, found in the rainforests of Vietnam, is distinguished by its red-and-maroon-colored legs. The species also has gray, black and white coloring, and powder-blue eyelids. Their numbers have fallen, experts say, because of hunting and because of the loss of habitat through deforestation.

"Douc langurs are hunted for food, for use in traditional medicine and for sale as pets," the World Wildlife Fund (WWF) said. "Laws aimed at protecting them are not always effectively enforced."

Toi was actually born in the San Diego Zoo in 1997, WCAU reported. The monkey was moved in 2009 to Philadelphia, where she lived the rest of her life.

Toi was a favorite among visitors to the zoo, and on social media. While the decision to say goodbye was a difficult one, zoo officials said it was the right one, The Philadelphia Inquirer reported.

The zoo's remaining primates include the white-faced saki, the western lowland gorilla and the common squirrel monkey, among others.