Ozzie, the world's oldest male gorilla, is dead at 61. Zoo Atlanta, where Ozzie lived, said he was found dead by his care team on Tuesday after his appetite had decreased last week. His cause of death is still unknown.

Ozzie was the zoo's oldest gorilla and the third-oldest gorilla in the world, after two female gorillas – Helen, who turned 64 at the Louisville Zoo earlier this year, and Zoo Berlin's Fatou, whose 65th birthday is in April.

Ozzie was a western lowland gorilla, which are critically endangered, according to Zoo Atlanta.

Gorillas are considered geriatric at about age 40, according to the zoo, which says Ozzie's longevity "is a testament to the care, expertise and significant innovations of the Zoo's Gorilla Care Team, which has become renowned for the care of geriatric gorillas."

While receiving care last week, Ozzie started showing symptoms including facial swelling, weakness and inability to eat or drink. The University of Georgia Zoo and Exotic Animal Pathology Service in the College of Veterinary Medicine will perform a necropsy to determine the cause of death.

Ozzie came to Zoo Atlanta in the 1980s and before he died, he was the only surviving member of the original generation of gorillas brought to the zoo's Ford African Rain Forest in 1988.

He is survived by his children, Kuchi, Kekla, Stadi and Charlie, granddaughter Lulu, and great-grandchildren Andi and Floyd, who all live at Zoo Atlanta. He also has several relatives living at other zoos in the U.S. and Canada. 

Poaching, illegal hunting for the bushmeat trade, habitat loss and emerging diseases have reduced western lowland gorilla populations by 60% over a 25-year period, according to the International Union for the Conservation of Nature. Some areas have declined as much as 90%, Zoo Atlanta says.

The loss of Ozzie is "devastating," Raymond B. King, president and CEO of Zoo Atlanta said. "Ozzie's life's contributions are indelible, in the generations of individuals he leaves behind in the gorilla population and in the world's body of knowledge in the care of his species. Our thoughts are with his care team, who have lost a part of their lives and a part of their hearts."