Posted by: Gigi Allianic Leo, a 40-year-old male gorilla, passed away suddenly on March 29, 2018 after a brief illness. Photo by Dennis Dow/Woodland Park Zoo. Leonel, a male gorilla fondly called Leo, passed away last night at age 40 after a brief illness. The upper middle-age gorilla had been under a 24-hour care this week. He died in his off-view sleeping den. On Monday, the 360-pound gorilla had no interest in food or drink, and did not want to leave his den to go outdoors. The zoo’s animal health team did a visual assessment and a 24-hour treatment plan that included medications, hydration, hand feeding and observation. Plans to anesthetize him yesterday for a diagnostic exam were canceled because Leo had shown significant signs of improvement. “Leo drank and ate a lot and urinated, a positive sign of hydration. Also, his activity levels increased and we even observed play behavior, so we believed he was on the mend,” said Nancy Hawkes, PhD, Woodland Park Zoo’s director of