Lincoln Park Zoo Euthanizes Oldest Male Chimp in North American Zoo System

Those at the Lincoln Park Zoo said they were saddened Monday by the loss of Keo, who was the oldest living male Chimpanzee in any North American Zoo.

Animal care staff made what officials described as "the difficult decision" to euthanize Keo on Sept. 30, they said. The geriatric male chimpanzee was suffering from advanced cardiac disease, which compromised his quality of life.  

Keo was 55 years old and the very first chimpanzee to live at the Lincoln Park Zoo, officials said. He arrived in Chicago in 1959 when he was just 1 year old. He has since sired 11 offspring. 

“Keo was an incredibly special individual," curator of primates Maureen Leahy said. "He was truly a member of our family and will be missed dearly. His long, rich life is a testament to the wonderful care he received here as well as the veterinary advancements that have been made in the past five decades.”

The median life expectancy for male chimpanzees living in zoos is 31.7 years, officials said. The longevity record is 61 years.

For the final years of his life, Keo lived predominantly behind the scenes at Regenstein Center for African Apes with two female chimpanzees, Vicky, and her daughter, Kibali.

“Keo was always full of personality, even as his health began to decline,” said Steve Ross, director of the Lester E. Fisher Center for the Study and Conservation of Apes. “I can speak for everyone who knew Keo when I say his loss is felt keenly, and working with him was a privilege that we will all treasure forever.”

Those at the Lincoln Park Zoo work to conserve chimpanzees through research conservation efforts in Goualougo Triangle, Republic of Congo and Gombe National Park, Tanzania. 

Project ChimpCARE, headquartered at Lincoln Park Zoo, is aimed at addressing chimpanzee welfare and conservation concerns across the U.S. 

The zoo also supports the Chimpanzee Species Survival Plan which helps ensure that the chimpanzee population in zoos throughout the country remains healthy. 

"Keo was a beloved individual and ambassador for his wild brethren," zoo officials said, in a statement. "The Lincoln Park Zoo family is saddened at his passing. A memorial page has been set up in his honor, and Keo fans and friends of the zoo are welcome to leave comments, share memories, or express condolences to animal care staff who are especially affected by this loss." 

Visit the memorial page here.