When lemurs grow old, their movements become slower and stiffer. They wobble on branches they could once easily grasp. Sometimes their tooth comb, a group of teeth used for grooming, falls out, making it more difficult for them to keep their coat fluffy on their own. So the best companion for a geriatric lemur is another geriatric lemur, one who doesn’t want to tumble but is content to sit together and help with care. “Young people can be too boisterous,” said Dr. Grebe.
To her credit, Cheyenne never settles for just any geriatric lemur. Some time ago, the caretakers tried to introduce Martine, a female lemur, to Chloris and Cheyenne. Chloris didn’t mind – a cordiality perhaps helped by her cataract. “She doesn’t care what anything looks like,” said Mrs. Keith. But Cheyenne showed her teeth, stared at the new lemur, and eventually chased her away. Ms. Keith said that Cheyenne could be bossy, but that Martine was notoriously unruly: “She wasn’t putting out the right vibes for Cheyenne.”
Still, Cheyenne and Chloris are open to elderly loners joining their D Wing residence. Until a few months ago, the lemurs lived with Pedro, a very old mongoose lemur who loved kiwis, until he died.
Wild lemur populations are often sympatric, meaning they live in the same geographic area. But according to Dr. Tecot, scientists have rarely observed that different species interact with each other. A 2006 study found that Madagascar’s crowned lemurs and Sanford lemurs formed a polyspecific association, communicating and coordinating their activities over time. Mating between lemurs of different species seems even rarer, if at all. Dr. Tecot, who co-directs the Ranomafana Red-Bellied Lemur Project in Madagascar, has never seen any combinations of mixed species in the wild.
In captivity, these pairs can provide insight into how lemurs can form interspecies companions, according to Ipek Kulahci, a postdoctoral researcher at the University of Notre Dame.
Cheyenne and Chloris, who both turn 33 in April, have run out of energy to play. But they still enjoy the sun in their outdoor enclosures and stay warm in their sleeping baskets, which are padded with fleece blankets to cushion their old bones.
In recent years, Chloris has had more forgetful episodes where she seems oblivious to where she is – calling her keepers “ senior moments, ” said Ms. Keith. But when Chloris returns to clarity, she sees in her good eyes that she’s still with Cheyenne.