One of North America’s oldest white-handed gibbons humanely euthanized at Toronto Zoo

Lenny the white-handed gibbon is seen in this undated photograph posted on social media by the Toronto Zoo.

The Toronto Zoo is mourning the loss of a 46-year-old white-handed gibbon, who was humanely euthanized over the weekend after a large mass was discovered in his abdomen.

According to officials, the gibbon, whose name is Lenny, started to show less interest in his food on Friday, sparking concern among his keepers.

“While these subtle changes may seem insignificant for other animals, his keepers and veterinary staff knew that those signs, combined with a recent decline in his weight, could be a reflection of a serious issue,” the zoo said in a post on social media.

It was later discovered that Lenny had a large mass in his abdomen and an enlargement of his stomach and intestines.

“His weight loss suggested a chronic progressive process and given the high likelihood of a tumour, we made the very difficult decision to humanely euthanize Lenny that afternoon,” the zoo said.

The zoo said that it appears as though the mass was within the intestinal wall and was slowly growing, causing little issue until it became large enough to cause a blockage.

White-handed gibbons are considered seniors at age 35, so Lenny, at age 46, was one of the oldest of his kind in an accredited zoo in North America. He spent many of his days with Holly, who is 49 years old, “duetting in the early mornings.”

“Many know Holly for always carrying around a stuffed animal, but Lenny would also do this too, especially when he was settling down for the night,” the zoo said.

“Holly was given the chance to say goodbye to Lenny after he passed. Since Saturday, Holly has been calling more than usual, but she has been eating, training, and participating in her normal care routine.”

Keepers will be monitoring Holly and giving her extra attention as she adjusts to life without Lenny.

White-handed gibbons are small apes that are native to southeast Asia. They are listed as endangered in the wild.