Aye-Aye, Daubentonia madagascariensis
AYE-AYE
Daubentonia madagascariensis
Geographic Distribution and Habitat
The elusive and sorely misunderstood aye-aye, the oldest type of living lemur, is endemic to Madagascar, the fourth largest island in the world. Situated off the coast of East Africa, Madagascar is home to an abundance of unique animals and plants that cannot be found anywhere else on the planet.
It is within this richly biodiverse environment that the solitary, nocturnal aye-aye thrives. He is equally comfortable in the island’s eastern rainforests and drier southern areas as he is in the north of the island, where windy and warm winters and hot and humid summers prevail. He has been known to make his home in both deciduous forests and seaside disturbed secondary forests, as well as in mangrove swamps, dry scrub forests, and, to his own peril, in areas where the risk of human conflict is high, such as cultivated sugar cane, clove, and coconut plantations.
Although populations of aye-aye occur in low densities and isolated pockets, the aye-aye is now thought to be more wide-ranging than previously suspected; up until the mid-1900s, the aye-aye was believed to be extinct. Researchers now believe the aye-aye has one of the largest distribution ranges, albeit fragmented, of all non-human primates across Madagascar’s 227,000 square miles (587 sq km). In fact, the only area of Madagascar the aye-aye has not been found in is the southwest, where the spiny forest lacks suitable food and trees for nesting.
Human-assisted aye-aye breeding colonies also exist, most notably on the island of Nosy Mangabe, found on the east coast of Madagascar, and at the Duke University Primate Center in Durham, North Carolina.
Size, Weight, and Lifespan
Weighing in at about five pounds (2.5 kg), the aye-aye is the largest of all nocturnal primates. His head and body measure about 17 inches (43.2 cm), but he has an impressive bushy tail that measures longer than his body at roughly 24 inches (61 cm). As with most lemur families, aye-ayes do not exhibit significant sexual dimorphism, which is distinct differences in size or appearance between the sexes of an animal in addition to differences in the reproductive organs.
In the wild, aye-ayes are thought to live 20 years, and as long as 24 years in captivity.
Appearance
Perhaps more than any other primate, and especially within the context of the generally cute lemur superfamily, aye-ayes suffer from a set of ghoulish physical features that have led some to view them as harbingers of death. With sharp teeth, pointy claws, and yellow-orange eyes, the aye-aye was even once misclassified as a rodent.
Primatologists now know better. The harmless aye-aye’s extraordinary features inspire curiosity and wonder at the elegance of her unique morphological adaptations. She has a nocturn’s large eyes, and oversized, movable leathery ears thought to aid in percussive foraging for insects and larvae inside hollowed branches. Her large, sturdy hands come equipped with curved claws and long fingers that excel at grasping branches while foraging. Likewise, her feet have curved claws on all digits except her opposable big toes, which are used to dangle from branches.
Most distinctive is her elongated, bony middle finger. While folklore says she uses this finger to pierce the heart of humans, the truth is far more interesting. The middle finger is an all-purpose tool she can use to scoop pulp from fruits (coconuts and ramy nuts are favored) and insects from branches, consume liquids, and self-groom. Equally impressive is how she uses her middle finger to tap along branches, presumably listening for the cavities where insects might be found, similar to how a woodpecker forages. Some researchers, however, suggest that the tapping behavior may not rely on auditory clues, but rather on touch.
Duke University scientists learned that an aye-aye, like humans, apes, and some monkeys, can move her middle finger independently, suggesting high levels of motor cortex development—something that is not commonly seen in lemurs and other prosimians.
Another unique adaptation seen in the aye-aye and not in other primates is the gift of ever-growing incisors, assuring she always has strong, sharp teeth to gnaw through wood, nuts, and hard-shelled fruits. She also has a third eyelid, known as a nictitating membrane, that helps protect the eye from debris when she is gnawing through branches.
With a pale face and a short muzzle, the aye-aye’s coat is a slate grey-brown with white flecks of long guard hairs. In some mammals, long, coarse hairs protect the softer layer of fur below. The bushy tail also features long hair—measuring over nine inches (22.9 cm), the longest of any prosimian.
Diet
The omnivorous aye-aye relies on a diet that is rich in fats and proteins. In addition to staple insects, grubs, and larvae, he favors bananas, ramy nuts, and coconut. To some degree, he’s not a very picky eater; depending on food availability and his locality, he will also happily consume seeds, nectar, lychees, mangoes, and bamboo.
Behavior and Lifestyle
Although not thought to be strictly solitary, aye-ayes spend a great deal of their time alone, loitering as high as 60 feet (18 m) up in the tree canopy, either foraging at night or curled into ball-like nests during the day. For these reasons, sightings of the aye-ayes are rare, with their presence often being detected by tree hole marks and empty nests.
Normally, one would not think it’d be hard to mistake a primate for a rodent, but not so in the case of the aye-aye. So unusual is the aye-aye’s appearance that the species was once classified as a rodent. Now, due to its specialized traits and distinctiveness from other lemurs, the aye-aye is categorized as its own family, genus, and species.
Today, the aye-aye is the only living member in the family Daubentoniidae. Researchers have found fossils of a larger, related species, Daubentonia robusta, in the dry southwestern spiny forests of Madagascar, the only area on the island where aye-ayes currently do not exist.
An aye-aye nest is an elaborate oval construction of leaves, twigs, and branches with a single-entry hole. It is there where the solitary aye-aye spends the majority of his day sleeping alone, although some male pairings have been seen in a single nest. He does not always return to the same nest day after day, and several aye-ayes may share the same nest on different days.
At just before sunset, he emerges and begins his nightly routine: quadrupedally walking (on all fours) and rapidly climbing up and down tree trunks and through the canopy in search of food, avoiding descending to the forest floor whenever possible. Notably, the aye-aye’s strong arms and sturdy opposable big toe allow him to climb headfirst down tree trunks. While many other lemurs and closely related lorises use a vertical “clinging and leaping” style of locomotion, the aye-aye does not.
Unlike other African primates, the aye-aye possesses functional claws, including a toilet claw that he uses to groom himself during the night. While awake, he will spend intermittent periods resting, sometimes using his claws to rest vertically or cling upside down on branches.
Despite his reputation for being a loner, the aye-aye is not entirely anti-social: researchers have documented pairs of aye-ayes foraging together, as well as establishing nests near to one another.
Males have home ranges that spread out across as many as 500 acres (200 ha), overlapping with other males. Females, on the other hand, have much smaller ranges—less than 125 acres (30 ha)—that overlap with at least one male but rarely overlap with other females. Individuals will mark their home range by rubbing parts of their neck, cheeks, and rump regions, where scent glands exist, onto branches.
The aye-aye’s nocturnal work continues well through the night, and sometimes he may not return to a nest until several hours after sunrise.
Aye-ayes are relatively quiet, occasionally communicating with brief cries. A scream can indicate aggression or protest, while a small, descending whimper suggests competition over food resources. Researchers have noted that other sounds, such as a “tiss” sound and a “hai” sound, are used in the presence of humans or when fleeing.
While aye-ayes may be solitary in most aspects of their lives, this is not true during courtship and parenting, when high levels of interaction do occur.
Mating season is not restricted to one season. Females begin breeding at three or four years of age, giving birth to one infant every two to three years thereafter. A mother will become dominant over males while parenting, presumably giving her better access to food while rearing offspring. The infant will stay within a nest for as long as two months before finally emerging, but it will be another seven months before the infant aye-aye is able to navigate the canopy as well as an adult. Among lemurs, this represents a relatively slow rate of development and demands high levels of parental investment.
As partial frugivores (fruit-eaters), aye-ayes may help regenerate forests by dispersing seeds throughout the forest. They are also considered to play an important role as predators of wood-boring beetle larvae.
The aye-aye was once considered one of the most endangered mammals in the world, but new research on the aye-aye in Madagascar has confirmed that the species is far more widely distributed than first believed. However, the primate remains listed as Endangered on the International Union for Conservation of Nature’s (IUCN, 2012) Red List. In its 2016-2018 and 2018-2020 Primates in Peril Reports, the conservation advocacy group Global Wildlife Conservation listed the aye-aye on its list of the world’s 25 most endangered primate species.
The IUCN reports that the aye-aye has seen its numbers decline by more than 50% over three decades, and predicts a similar rate of decline over the next 10-24 years. The biggest threat to the aye-aye is the widespread deforestation that continues to put all of Madagascar’s primates at risk.
The aye-aye’s strange and menacing appearance has not helped the species garner protection among locals, who see her as an ill omen and a harbinger of bad luck. It is not uncommon for an aye-aye to be killed by humans, either because of superstition or because she is seen as a crop pest.
Aye-ayes may also be hunted by fossas (Cryptoprocta ferox), a large carnivore found in Madagascar.
The Convention on International Trade in Endangered Species (CITES) of Wild Fauna and Floral includes the aye-aye on Appendix I, its listing of most endangered wildlife
A number of breeding and conservation programs have been established to help protect the aye-aye, including at the Duke Lemur Center in Durham, North Carolina. At least 16 areas across Madagascar and on the nearby island of Nosy Mangabe have been designated for the protection of aye-ayes. As of 2010, there were roughly 23 captive aye-ayes in the United States, with another 27 captive aye-ayes around the globe.
The aye-aye’s elusiveness and fragmented populations make it difficult for conservationists to estimate populations in the wild, and the IUCN notes that there is an urgent need for a systematic census to be conducted on aye-ayes in Madagascar so that a comprehensive conservation action plan can be developed.
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Written by Christine Regan Davi, February 2018