Yesterday, the Nashville Zoo celebrated the 40th birthday of Muffy, a white-cheeked Gibbon. “She still climbs trees up to the top with [the male gibbon], and they do their duets several times a day, so she is still pretty active. She does have some problems just like an older person, like arthritis. That slows her down a little bit, but we’re really glad she’s able to move pretty well,” said zoo employee Emily Johnson. Muffy celebrated her birthday with a treat of ice filled with fruit,