Zoo staff made the difficult choice to euthanize one of the zoo’s two female mountain lions, Sierra, earlier in the week. Officials said 17-year-old Sierra was suffering from advanced kidney failure.

The Phoenix Zoo lost one of its longtime residents this week. Sierra, a mountain lion, was humanely euthanized due to advanced renal failure. Sierra and her sister, Mystic, came to the zoo as cubs ...

Phoenix Zoo's mountain lion, Sierra, dies After 17 long years at the Phoenix Zoo, Sierra the mountain lion was humanely euthanized after experiencing renal failure, the zoo said on Feb. 27.