Alan Mothner
FILE - In this Nov. 24, 1997, file photo, researcher Lyn Miles signs to Chantek the orangutan at Zoo Atlanta in Atlanta. The zoo says Chantek died at the age of 39 on Aug. 7, 2017. (AP Photo/Alan Mothner, File)

ATLANTA (AP) — An orangutan who communicated with researchers using sign-language has died at an Atlanta zoo. Chantek was 39.

On its website, Zoo Atlanta says Chantek died Monday. The cause of death isn't known, but the zoo says veterinarians had been treating him for progressive heart disease.

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Chantek came to the zoo in 1997 at the age of 19. He was born at Atlanta's Yerkes Language Research Center and spent nine years living with researchers at the University of Tennessee-Chattanooga. Researchers raised him like a human child and taught him at least 150 words in American Sign Language. He was taught other human skills such as using a bathroom and cleaning his room.

Zoo Atlanta says Chantek was given a "naturalistic" living environment with other orangutans once he arrived there.

A post-mortem exam of the ape is scheduled to be performed.