The Uncommon Aye-Aye: An Interview with Eleanor Sterling

The dozens of diverse lemur species on Madagascar are a motley crew. Still, none look and act quite like the aye-aye. In fact, this lemur is considered one of the world's strangest animals altogether. Just ask Eleanor Sterling: she's a conservation biologist, the director of the Museum's Center for Biodiversity and Conservation, and one of the world's few experts on the aye-aye.

An aye-aye amid greenery.
An aye-aye on Nosy Mangabe, a small island and nature preserve in Antongil Bay, Madagascar. Being nocturnal canopy-dwellers, aye-ayes are notoriously difficult to photograph in the wild. Note the animal's special elongated middle digit. Peter Ersts for AMNH

What makes the aye-aye so strange?

First off, it’s got continuously growing front teeth like a rodent. It has a really thin middle finger that is mostly tendon and bone. A protective film also covers its eye when it is gnawing wood and bits are flying everywhere. These features are not found in any other lemur nor any other primate, even. Most animals have behavioral characteristics that allow them to adapt well to their environment, but very few animals have such extreme morphological changes in body form and shape.

How do those adaptations help it survive?

Its features make it exquisitely well suited to acquire food, including insect larvae. Larvae live inside chambers in tree trunks and branches. The aye-aye taps along a branch with its funny finger and listens carefully with its large ears. It echolocates where larvae might be, opens up the chamber with its teeth, then sticks a finger in and pulls one out.

I’ve seen aye-ayes eat really big, chunky larvae just like a child eating an ice cream cone. First it bites the little head off and spits out the mouth parts—those are hard to digest. The insect’s insides then drip down the aye-aye’s fingers, so the animal runs it tongue around its hand to lick the juicy parts up fast.

Sounds tasty.

Well, larvae are high in both fat and protein, so they’re good for both quick and long-term energy. And if you can gain access to hard-to-acquire, “structurally defended” food sources like larvae with your specialized adaptations, you don’t have a lot of competition from other animals.

An aye-aye in captivity in a room with a white brick wall. Its pale face focused on the camera, it is clinging to a vertical stick.
An aye-aye in captivity at the Duke University Primate Center in North Carolina. Duke University Primate Center/ David Haring

So does that mean the aye-aye is smarter than other lemurs?

Not necessarily. The finger is certainly very advanced in its manipulative abilities. It has incredible flexibility—aye-ayes can move it 360 degrees around the joint with the hand. Interestingly, the aye-aye has an enormous brain for its body size compared to that of other lemur species. The mechanics of its manipulative operations and the sophisticated echolocating ears might explain the size of the brain.

Why else does the aye-aye look like it does?

It has dark fur and big bright eyes because it lives in a dark rain forest. It is well specialized for nocturnal living. The eyes are designed to pick up any available light, even on a night with very little moonlight, and reflect it to discern the smallest changes in the environment. Aye-ayes also have very acute senses of smell and hearing.

How did you become so well acquainted with these animals?

I lived on a little island off the coast of Madagascar called Nosy Mangabe for about two years studying aye-ayes for my doctoral thesis. I conducted the first long-term study of the animal, following single aye-ayes through the night to figure out exactly what they do, whom they meet, and how they interact with each other. Only a few researchers have studied aye-ayes in the wild since, as field conditions are very difficult. You have to put a radio telemetry collar on the animal to track it—a very expensive, difficult, and time-consuming project—then follow the aye-aye for the life of that collar, which can be months. It’s only after following individuals through the seasons that you get a sense for how they live their lives.

A woman, Eleanor Sterling, with a brown lemur in a tree in the Seychelles islands where several species of lemurs have been introduced.
Eleanor Sterling with a brown lemur on the Seychelles islands north of Madagascar, where several species of lemurs have been introduced. Kevin Frey

What was it like following aye-ayes so intensely for two years?

It was one of the most amazing experiences of my life. There were no roads—just barely paths—and I lived in a tent surrounded by the sea. I would wake up in the afternoon and start work at 5 p.m. to find where a radio-collared aye-aye was sleeping in a nest. I’d wait for it to wake up, then two other people would keep the aye-aye in the crossbeam of their flashlights while I would watch it with binoculars. We’d follow it all night over rugged mountainous terrain, and I was trailing headphone wires and antennae that constantly got caught in the thick vegetation we were wading through. Aye-ayes can move easily in the canopy, but I would have to go down and up and down on the ground, leaping over dark canyons and doing other Herculean things to keep up. If I lost the animal, I had to go back to the tent and start again the next night. It was interesting to get to know an animal as well as we did, to get a sense for not just how it lives but how we can do a better job of conserving it.

What is the conservation status of aye-ayes on Madagascar? 

We know there was another kind of aye-aye once. It was bigger than the existing species and lived when humans first arrived on the island about 2,000 years ago. The paleontological evidence for it includes teeth with holes bored in them, so humans may have used the teeth in some kind of jewelry. That aye-aye is now extinct. We don’t know why or how just yet.

As for the smaller aye-aye that now remains, people were unclear about the animal’s status for a long time. Some of the French explorers in the early 1900’s noted that it was quite rarely encountered on Madagascar. In fact, in 1935 they declared it extinct, because they hadn’t seen it in a while. Then a group of scientists from Paris visited Madagascar in the 1950’s and found a couple of aye-aye populations. They captured nine aye-ayes and put them onto the island of Nosy Mangabe as a protected reserve.

Are aye-ayes really that rare?

We know that the chances of people running into an aye-aye are much lower than for diurnal lemurs, which come out during the day. Aye-ayes tend to wander about alone and don’t congregate often. So you have to be at the right time and place to run into one.

Today, we can tell definitively that an aye-aye has been in an area by the particular marks they make on nuts they crack open. The good news is that aye-ayes are fairly widely distributed around Madagascar. But we still don’t know the population size in any one of those places. There’s a lot more work on the aye-aye that needs to be done.

Related Links

Three eccentric circles, red with white outlines, against a gray background.

   AMNH: Eleanor Sterling's home page

Three eccentric circles, red with white outlines, against a gray background.

   AMNH Ology: Eleanor Sterling

Three eccentric circles, red with white outlines, against a gray background.

   Duke University Primate Center: Aye-aye fact sheet