Silverback gorilla Ndume picks up a toy at The Gorilla Foundation's preserve in California's Santa Cruz mountains. Photo: Ron Evans/Cincinnati Zoo and Botanical Garden via AP.

A federal judge in San Francisco has sided with the Cincinnati Zoo in its dispute with a Bay Area nonprofit over the fate of longtime companion of Koko, the western lowland gorilla who famously learned sign language.

In a decision issued Friday, U.S. District Judge Richard Seeborg ordered The Gorilla Foundation, the Redwood City nonprofit that cared for Koko until her death in June 2018, to begin working with the zoo to arrange the transfer of Ndume, Koko's male companion.

The zoo loaned Ndume to the foundation nearly a quarter century ago in hopes that he and Koko would mate, but they never did. Seeborg ruled Friday that the foundation had entered into a valid agreement with the zoo prior to Koko's death to let an organization that oversees the well-being of captive gorillas in North America decide where Ndume should live in the case that he outlived Koko.

That organization has determined that Ndume should return to the zoo where he can interact with other gorillas. After Koko's death, he was the sole remaining gorilla housed at the foundation.

The foundation's lawyers at Casselman Law Group and Cotchett, Pitre & McCarthy had argued that Ndume's age, 27 years of experience living under the foundation's care, and a dormant stomach infection would make any move a serious risk to the gorilla's health. But Seeborg concluded that the foundation was aware of those risks when it signed an updated agreement with the zoo in 2015.

Related story: Gorilla Foundation Moves to Sideline PETA in Fight Over Koko's Companion

“TGF's position is fatally undermined by the fact it made the agreement only three years ago, with full knowledge of the facts it now insists might give rise to unreasonable costs,” Seeborg wrote.

The judge, however, directed the zoo to entertain “in good faith” any suggestions the foundation has regarding Ndume's transfer and care.

“TGF, in turn, is to exercise the utmost good faith in presenting any suggestions or requests, and is directed to bear in mind that the question of whether Ndume will be transferred to the Zoo is no longer subject to negotiation,” the judge wrote.

Seeborg urged the parties to reach a consensus on the transfer noting that Ndume is “no ordinary chattel.”

“While the law recognizes that gorillas in captivity may be owned, neither the 2015 Agreement nor this order treats Ndume merely as property to be dealt according to the desires of the Zoo,” the judge wrote. He asked the parties to file a joint statement if they were at an impasse on any issues within 30 days of his Feb. 1 order.

Reached by email Monday, the foundation's lead lawyer, David Casselman of the Casselman Law Group, said his client is reviewing the situation and had no comment.

Counsel at Covington & Burling and Taft Stettinius & Hollister represent the zoo.

In a written statement, a spokesperson said that zoo was pleased that the judge was enforcing its agreement with the foundation as it is written.

“We look forward to working with The Gorilla Foundation to transfer Ndume to Cincinnati safely as soon as possible, so that he can once again live with other gorillas,” the spokesperson said.

Delcianna Winders, vice president and deputy general counsel of PETA, which filed an amicus brief backing the zoo in the case, issued a statement calling the ruling “a new life for Ndume the gorilla and … an official court declaration that an intelligent, sensitive gorilla is 'not ordinary chattel.' ”

“ We look to The Gorilla Foundation to follow the court's order and cooperate with the Cincinnati Zoo without delay so that Ndume can finally be supported by expert care and have the essential companionship of his fellow gorillas,” Winders said.