World's oldest blue-eyed black lemurs celebrate birthday

March 16 (UPI) -- The world's oldest blue-eyed black lemurs, Stewart and Bardot, are celebrating their birthdays, the Philadelphia Zoo announced.

Stewart turned 32 this past week, making him the oldest male blue-eyed black lemur, and Bardot turned 30, making her the oldest female blue-eyed black lemur.

"Blue-eyed black lemurs and spider monkeys are the only two primates other than humans that have true blue eyes. We're so thankful to have such an incredible animal care team and vet staff to keep this couple healthy and happy in their golden years," the Philadelphia Zoo said on Twitter.

Blue-eyed black lemurs are sexually dimorphic, which gives males and females different colors. Stewart has black fur while Bardot has tan fur.

The species is critically endangered and are considered to be one of the most threatened primates on the planet.