The chimpanzee was often found in the center of any grooming session and enjoyed relaxing in the sunshine in a nest she built herself, Zoo personnel said.

ST. LOUIS -- Saint Louis Zoo lost a kind soul on Thursday when they humanely euthanized a 55-year-old chimpanzee who's been a staple at the zoo for the past 17 years.

Rosebud, known by her friends as "Rosie," was euthanized due to progressive arthritis that stopped responding to pain medication, zoo personnel said in a Facebook post. She reportedly had other medical concerns often seen in geriatric animals, but care received from the zoo's primate and animal health team allowed her to live a long life.

The average life expectancy for a chimpanzee in captivity is 39.2 years, according to the Kyoto University Wildlife Research Center.

"Over the last four years, Rosie was able to see her granddaughter Raven's birth and development and she played a huge role in helping Utamu as a first-time mother," the zoo's post said. "She was often found in the center of any chimpanzee grooming session and enjoyed playing with the other chimpanzees. Her favorite activity was relaxing in the sunshine in a big nest she built herself."

The zoo's Jungle of the Apes care team said Rosie was "simply the best," and that she'd often greet them by making "raspberry" vocalizations when they were delivering bananas, her favorite food.

"Rosie will be greatly missed by her chimpanzee family, caretakers and all who knew her," the post said.

The Saint Louis Zoo has a specific institute focused on the conservation of Congo apes, as only an estimated 150,000 exist in the wild today. The WildCare Institute Center for the Conservation of Congo Apes works to develop conservation policies geared toward the long-term survival of chimpanzees and gorillas within the Congo Basin.