As lemurs get older, their movements become slower and more rigid. They wobble on branches that they once could easily grasp. Sometimes their tooth comb, a group of teeth used for grooming, falls out, making it difficult for them to keep their fluffy fur on their own. A geriatric lemur’s best companion, then, is another geriatric lemur, someone who doesn’t want to fall but is content to just sit together and help with the grooming. “Young people can be too rowdy,” said Dr Grebe.
To her credit, Cheyenne never settles for just any geriatric lemur. Some time ago, the keepers attempted to introduce Martine, a female ring-necked lemur, to Chloris and Cheyenne. Chloris didn’t care – a cordiality maybe helped by her cataracts. “She doesn’t care what anything looks like,” Ms. Keith said. But Cheyenne bared her teeth, looked at the new lemur, and eventually chased her away. Ms Keith said that Cheyenne could be bossy, but Martine was notoriously broken: “She wasn’t broadcasting the good vibes for Cheyenne.”
Nonetheless, Cheyenne and Chloris are open to elderly singles joining their enclosure in the D-wing. Until a few months ago, lemurs lived with Pedro, a very old mongoose lemur who loved kiwis, until his death.
Populations of wild lemurs are often sympatric, meaning they live in the same geographic area. But scientists have only rarely observed different species interacting with each other, according to Dr Tecot. A 2006 study found that crowned lemurs and Sanford lemurs in Madagascar formed a polyspecific association, communicating and coordinating their activities over time. Pairing between lemurs of different species seems even rarer, if at all. Dr Tecot, who co-leads the Ranomafana Red-Bellied Lemur project in Madagascar, has never seen any mixed species pairing in the wild.
In captivity, these pairings may offer insight into how lemurs can form interspecific mates, according to Ipek Kulahci, a postdoctoral researcher at the University of Notre Dame.
Cheyenne and Chloris, who will both turn 33 in April, no longer have the energy to play. But they still enjoy the sun in their outdoor enclosure and stay warm in their sleeping baskets, which are stuffed with fleece blankets to cushion their old bones.
In recent years, Chloris has had more forgetful episodes in which she doesn’t seem to know where she is – her caretakers call them ‘senior moments,’ Ms Keith said. But when Chloris returns to lucidity, in her good eye, she sees that she is still with Cheyenne.