BUFFALO, N.Y. (WIVB) — The Buffalo Zoo is saying goodbye to a longtime resident.

Kayin, a 7-year-old western lowland gorilla, has moved from the Buffalo Zoo to his new home at the St. Louis Zoo in Missouri.

The move came per a recommendation by the Association of Zoos and Aquariums (AZA). According to the zoo, western lowland gorilla populations have declined by more than 60 percent in the past 25 years. This has been due to habitat loss, poaching, illegal hunting and emerging diseases, the zoo said, citing the International Union for Conservation of Nature (IUCN).

While at the Buffalo Zoo, Kayin lived in a family troop with his parents, aunt and half-sister.

“At 7 years old, Kayin is reaching the age when free-living male gorillas will typically leave their family group in the wild in search of a new bachelor group or mating partner,” the Buffalo Zoo said.

At the St. Louis Zoo, Kayin will live among three adult male gorillas, also known as “silverbacks.”

“Bachelor groups are groups of silverbacks and young adult male gorillas that live and travel together and are a type of social group commonly found in the wild.”