JoJo (Brookfield Zoo/CZS)

The Chicago Zoological Society on Aug. 1 announced the sudden death of JoJo, the 42-year-old silverback western lowland gorilla who had sired three offspring at Brookfield Zoo during his 10 years there.

JoJo’s death was announced in a post on Brookfield Zoo’s Facebook page. According to the post, the gorilla “went into cardiac arrest during an emergency veterinary procedure prompted by an acute illness” on July 31.

There was no additional information provided on the acute illness or the procedure undertaken to treat it. Zoo spokespeople reportedly were not available to address JoJo’s death.

When he arrived at Brookfield Zoo in June 2012, JoJo was a popular attraction at the Tropic World exhibit along with the zoo’s three female gorillas, Binti Jua; Koola, who is Binti Jua’s daughter; and Kamba, who is Koola’s daughter.

JoJo was 32 at the time and replaced 44-year-old Ramar as silverback. Ramar entered “semi-retirement” upon JoJo’s arrival and was euthanized in 2018 at the age of 50 after suffering an intestinal blockage.

JoJo came to Brookfield Zoo as part of the Association of Zoos and Aquariums’ Gorilla Species Survival Plan. Western lowland gorillas are considered critically endangered due to the loss of habitat, poaching and illegal pet trade.

He previously was at Lincoln Park Zoo in Chicago, where he sired a female in 2004, and at the Louisville Zoo, where he sired an offspring in 2003.

Keepers thought highly of JoJo. In the post announcing JoJo’s death, Brookfield Zoo stated, “JoJo was very smart and learned new behaviors quickly during husbandry training sessions. He was known for keeping order in the gorilla group by quickly breaking up squabbles and often showed his gentler and patient side when interacting with his offspring.”

Considered “an excellent genetic match” for the three female gorillas at Brookfield Zoo in 2012, JoJo would sire three offspring with two of them.

In 2013, a female gorilla, Nora, was born to Koola. Two years later, in 2015, JoJo sired a male, Zachary, with Kamba. In 2018, Koola bore JoJo’s third offspring, Ali.

At 42 years old, JoJo was considered a geriatric animal, according to Brookfield Zoo’s Facebook post.

“A median life expectancy for male gorillas in managed care is 32 years,” the post stated. “The loss of JoJo is great, but his legacy will live on in the overall zoo population for this critically endangered species.”

With the death of JoJo, Brookfield Zoo has six gorillas – Binti Jua, 34; Koola, 27; Kamba, 17; Nora, 8; Zachary, 6; and Ali, 4 — in its collection. However, his death leaves the collection without a silverback, though that may be temporary.

“Our Animal Programs staff is working with the Association of Zoos and Aquariums’ Species Survival Plan about bringing a silverback to the zoo,” said Sondra Katzen, director of public relations for the Chicago Zoological Society, in an email.