News Backgrounder: Duke Primate Center Successfully Fosters Mysterious Aye-Ayes

July 08, 1998

DURHAM, N.C. -- The goggle-eyed, bat-eared little ball of wiry fur was nicknamed "Starvin' Marvin," because he had been rejected by his mother, who had become ill immediately after birth last February.

But the Duke University Primate Center veterinarian and animal technicians resolved that Marvin wouldn't starve for long. They set out to save the little creature, known as an aye-aye, by hand-raising it -- the first time such a full-scale attempt had been made on an infant member of this endangered species.

Their dedicated efforts exemplify the center's hard-won success over the last decade in managing and breeding a creature that easily wins the contest for the strangest primate on earth. The nocturnal aye-aye resembles a cross between a bat, a beaver and a raccoon. It has been compared to a gremlin, a gargoyle, and even the fabled Jabberwocky with its "slithy toves."

So queer is the aye-aye that when it was discovered in the 18th century, zoologists first classified it as a squirrel or even a kangaroo. When they finally realized it was a primate, they gave it a scientific name, Daubentonia madagascarensis, that made it the sole member of its genus.

The aye-aye's eerie appearance -- which led the Duke primatologists to bestow spooky names such as Nosferatu, Poe and Morticia on the animals -- also works against its survival in its homeland of Madagascar. Superstitious Malagasy believe that if an aye-aye points its finger at them, they're doomed to die, so they kill the animals on sight when they encounter them during the day.

True to its patchwork appearance, the aye-aye is a bundle of behavioral contradictions. Its powerful jaws can gnaw through a concrete block wall, yet it is so naturally gentle that when technicians have had the startling experience of an aye-aye inserting its long finger deep into their ear to probe for tasty insects, they have felt only a delicate tickle.

The aye-aye shows an extraordinary skill at detecting insects hidden beneath tree bark by tapping its way along a trunk, big ears cupped over the wood, using its keen hearing to distinguish tiny subsurface hollows. It then gnaws into the wood and uses its long finger to fish out the morsel. Yet despite such cleverness, when presented with food in a bowl, an aye-aye may not even realize that the food is to be eaten.

And despite the aye-aye's distinctive homeliness, the animals inspire a warm affection in their keepers and in Primate Center visitors.

The battle to save Marvin -- who hasn't received an official name since his survival remained uncertain -- began with a round-the-clock feeding schedule. Every two hours, Primate Center veterinarian Cathy Williams and staff members took turns feeding the infant a concentrated version of a human infant formula through a nipple-tipped syringe.

Williams also has launched a first-ever effort to analyze aye-aye milk, to better mimic it. Her project has presented the daunting prospect of milking the center's lactating aye-ayes -- potentially hazardous even with the amiable aye-aye, given their beaver-like teeth and jaws. However, the milking was accomplished, with one technician grasping the mother's hind legs, another the front, and a doggie chew-toy to distract the aye-aye. Williams is having the milk analyzed by the National Zoo in Washington, D.C.

Marvin's problem, said Williams, was that even with the frequent feedings, he just wasn't gaining weight as fast as another baby aye-aye, Kali, who stayed with its mother, Endora.

"I have a feeling that aye-aye milk is much richer than what we fed him," said Williams. "The milk composition of nocturnal lemurs, in which the infant stays in a nest and the mother comes and goes, is much higher in fat and protein. The babies have to get all their nutrition during the brief time the mother is in the nest."

The climax in the effort to save Marvin came in May, when Williams decided to try an experiment in inducing the mother to resume lactating. While Marvin's mother, Morticia, was somewhat cooperative in accepting Marvin when presented with him, she was not producing milk, and despite occasional attempts by Marvin to nurse, would not accommodate the infant.

"We found that a common drug used in humans to induce lactation had also been given to an orangutan at the Pittsburgh Zoo to induce lactation, so we decided to try it on Morticia," said Williams. "After experimenting with the dosages, Morticia began to lactate and to nurse."

Now, says Williams, Marvin is with his mother full-time and has even developed enough to begin eating solids, although he is still receiving some hand-feeding.

The birth of Marvin and two other aye-ayes this spring brings the total captive Primate Center population to 12, said director Ken Glander. The center is now confident enough of their knowledge of the animals that a breeding pair -- Merlin and Caliban -- has been loaned to the San Francisco Zoo, and another pair will head for the Bronx Zoo sometime during the next year. The center also has an unofficial ambassador aye-aye, Mephistopheles, whose adaptability and calm nature has allowed the center to loan him to zoos around the country.

"Since we've been successful in breeding aye-ayes, it now is important to send them to other facilities so that we distribute the risk of something happening to the captive population," said Glander.

When aye-ayes were first brought to the Primate Center in 1986, success was by no means assured, he said.

"We basically knew nothing about successfully housing and breeding these animals in captivity," he said. "Even though they'd been kept in captivity for a hundred years, since they hadn't reproduced, we weren't even sure how they would react to one another when paired in cages." However, once the animals' dietary needs were established, they proved to be among the easiest lemurs to maintain, Glander said.

Not that there haven't been challenges. For one thing, the curious, constantly active animals have proven far more destructive to their concrete block wall enclosures. Tapping away at the hollow cinderblocks, the creatures apparently believe they may harbor insects, and gnaw holes in the walls that must be covered with stainless steel sheeting. Also, since the animals are foragers, they prefer to work for their board.

"Their natural foraging technique is to dig things out to eat, so they're basically uninterested in food if it's just presented to them in a bowl," said Williams.

Thus, the technicians put the basic aye-aye diet, a gruel of monkey chow flavored with vanilla, into a hollow bamboo tube or other container so that the aye-aye has to fish it out to eat. As an occasional treat, the technicians also fetch from Duke Forest a rotten log that the animals can tear apart looking for grubs.

"These feeding methods are not directly a medical problem, but it's something you have to do to ensure the overall well-being of the animal," said Williams.

The Primate Center has developed its aye-aye diet and feeding techniques as a result of some difficult lessons learned from the young aye-aye Goblin, born in 1994.

"He was being fed a chow with all the vitamins he would need, but he wasn't eating enough because of the presentation," said Williams. "So, he developed a bone disease that would be the same as rickets in humans."

After consulting a zoo nutritionist, the Primate Center staff determined that the aye-aye diet was still low in some vitamins and minerals. For one thing, the animals weren't being challenged to forage, which would have increased their feeding.

Another major dietary problem was that, like children, the animals weren't eating enough of what was good for them. They greatly preferred fruit, even though the fruits provided too much carbohydrate and not enough protein and key vitamins and minerals.

"Once we reformulated the diet, all the aye-ayes are doing much better, with a better coat, better reproduction and better weight gain," said Williams.

Like many of the Primate Center lemurs, however, the aye-ayes still present a major challenge in understanding their physiology, said Williams.

This need for more physiological data was dramatized with the death of Goblin last year. Goblin began to grow weak and, despite attempts at treatment, died of heart failure.

"We didn't have the time to save him," said Williams. "But even if we could have done a cardiac workup on him, we would have had no data to compare it to," said Williams. Thus, she and her colleagues are now seeking to develop a thorough base of knowledge on the animals, including EKG and ultrasound studies of their heart and chest x-rays.

"We need even the most basic information on aye-ayes, as well as our other species," she said. "We need to know what normal values are, so that we can understand when they're having problems." To aid this treatment and studies of the center's animals, Williams is seeking donation of a medical X-ray unit and an ultrasound unit for the Primate Center.

"Now, we have to transport them to an animal hospital in a van, but in an emergency situation like Goblin's we just can't do that," she said.

Emphasizes center director Glander, "The aye-aye is still an extremely mysterious animal, with many unknowns. Even though we've been successful with them, we're still learning." As an example, he cites the remarkably strange breeding requirements of the aye-aye.

"We learned, to our surprise, that we have to house females near each other in order to trigger the reproductive cycle," he said. "We've had cases where two females were isolated, each with a mate, and neither of them cycled for years. Yet within a month of being housed in olfactory communication with other females, they both cycled and got pregnant." Glander speculates that females in the wild might use the scent of another female as a territorial or reassurance signal, but the phenomenon still remains mysterious.

To understand perhaps the biggest mystery -- how aye-ayes use their tapping to locate food -- Duke psychology professor Carl Erickson has spent the last seven years experimentally challenging the animals to perform feats of detection.

In his studies, he constructs puzzles consisting of mazes of insect-sized tunnels cut into the depths of pieces of lumber, then observes how the animals use their finger-tapping sonar to detect mealworms placed in the tunnels.

"Essentially, I've tried to understand what cues the aye-aye uses in finding prey beneath the wood surface," said Erickson. His first studies attempted to discover whether the animals' tapping was meant to disturb prey into tell-tale movement, or whether the animals were actually detecting subsurface hollows. He discovered that the animals were fascinated by the tunnels whether filled with mealworms or not, and whether they were hollow, stuffed with acoustical plastic foam, or even re-plugged with the same wood.

In an ultimate test, Erickson and then-undergraduate Luke Dollar decided they would make detecting the subsurface features as hard as possible for the aye-aye. First, they extracted plugs from wood blocks. Then, with two of the plugs, they applied non-toxic school glue and let it dry before reinserting the plugs. With two other plugs, they inserted the plugs coated with fresh glue.

"We found that the aye-ayes immediately went for the plugs that weren't fixed in place, even though they were so tight that you couldn't see them. We realized they didn't even need a cavity to detect, just a crack."

Now that he has established the limits of the aye-ayes detecting ability, Erickson is attempting to understand their foraging strategy. In his latest experiments, he has created subsurface mazes, and then refilled them with packed sawdust, just as a boring insect would leave behind as it ate through the wood. He next opened hollows in the sawdust at various places along the track, adding mealworms to some and nothing to others.

"I thought that the animals might tend to look for the ends of tracks, where the insect would most likely be," he said. "But I found that aye-ayes were just as good finding grubs midway along the track as at the end. And contrary to my earlier studies, it did seem that the actual presence or absence of prey made a difference."

Erickson also is exploring how infants acquire the tapping strategy. He has constructed large cavity-filled wood blocks with up to 50 cavities, so that mothers and infants can work together.

His studies will significantly aid the aye-aye's future survival, because understanding how the primates forage naturally is a key to preserving that ability. Such foraging will be literally a life or death skill if captive-born aye-ayes are ever to be returned to the wild.

"We now have enough of these young animals reaching maturity so that we can compare wild caught with captive born," said Erickson. "That's really important, because we want to make sure that we're giving them all they need to be real aye-ayes. If we ever think about re-introduction of these animals, we want to make sure they have all the skills that they need."

The Duke Primate Center, located in a section of Duke Forest, is home to 16 endangered lemur species, as well as six other "prosimian" (pre-monkey) species such as lorises and bushbabies. The center is supported by the National Science Foundation, Duke University and private donations.

For more information, see the center's web site at

Duke University

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