Aye-aye

The aye-aye's third finger is long, narrow and unusually mobile. As the animal walks along a branch, it taps the wood rapidly and angles its large ears toward the surface. Differences in the returning sound reveal cavities and tunnels made by wood-boring insects. Researchers call this percussive foraging rather than true echolocation: the aye-aye creates the sound by tapping a solid object and interprets the vibration and echo, instead of emitting calls into open air as a bat does.

Once a likely tunnel is found, the aye-aye uses its incisors to cut through bark and wood. The flexible finger then enters the opening, swivels through the tunnel and hooks out a larva. The same digit can scoop pulp from fruit or the contents of an egg. Its joint is capable of movement in several directions, making the finger more like a precision probe than a conventional primate digit.

The teeth are equally unusual. The front incisors grow continuously and sharpen through use, allowing the animal to gnaw hard wood and seed cases. Aye-ayes lack the toothcomb shared by most other lemurs. Their feeding-specialized hands also make ordinary gripping more difficult, but a small structure discovered near the wrist partly solves that problem. This pseudothumb contains bone and cartilage, has its own muscles and bears a fingerprint-like pad. It acts as an extra point of contact while the animal grips a branch.

Aye-ayes are endemic to Madagascar, where they have a wider ecological range than their rarity once suggested. They occur in humid rainforest along the east, dry deciduous forest in the west and northwest, mangroves, secondary growth and some plantations. Camera surveys and direct sightings have documented them in more parts of the island than older accounts recognized, but a broad range does not mean the population is secure.

Trees remain essential. Aye-ayes forage mainly in the canopy and build spherical sleeping nests from leaves, twigs and vines. A nest sits high in a tree fork and has a side entrance. One animal may maintain several nests, and different individuals sometimes use the same structure on different days. During the night aye-ayes also descend to the ground, especially when moving between separated trees.

Forest fragmentation changes that movement. An aye-aye can use secondary vegetation, but isolated patches expose it to people and reduce safe routes between feeding and sleeping sites. Plantations may offer coconuts, mangoes or lychees, yet feeding there can cause the animal to be treated as a crop pest.

The aye-aye is an omnivore, although insect larvae, nuts and seeds are especially important. Wood-boring beetle larvae provide fat and protein. Ramy seeds from Canarium trees are another favored food, and the animal also takes fruit, nectar, fungi and cultivated crops.

Different foods call for different uses of the same toolkit. On wood, the middle finger taps and probes. On a hard nut, the incisors open a small access hole and the finger removes the kernel. With soft fruit, the finger scoops pulp from the skin. Large ears help detect subtle changes beneath bark, while a strong sense of smell may guide the animal toward fruit and plant exudates.

This foraging style takes time to learn. Young aye-ayes follow their mothers for an extended period and practice manipulating food long after they begin eating solids. The slow development is one reason a female cannot produce young frequently.

Aye-ayes forage mostly alone. Female home ranges are commonly reported at roughly 30 to 50 hectares, while males may range across 100 to 200 hectares and overlap several females. Overlap does not create a stable troop like that of a ring-tailed lemur. Adults usually meet briefly, although two or three animals may tolerate one another at a rich feeding site.

Activity begins around dusk and can continue through most of the night. An animal alternates between traveling, tapping, feeding and grooming, sometimes hanging upside down to reach a branch. By day it curls inside a leaf nest.

Scent marks help identify occupied space. Aye-ayes also use several calls, including contact sounds, alarm or protest calls and aggressive screams. Their large ears are not only for locating food; they remain important in communication and in detecting danger in the dark.

Breeding can occur throughout the year. A female may mate with more than one male during an estrous period, and gestation lasts about 172 days. She usually gives birth to one infant and may not reproduce again for two or three years.

The infant remains in a nest at first, then begins exploring nearby branches. Solid food may enter the diet at around five months, but nursing and food begging can continue well beyond that point. Young animals need months of practice before their movement and extractive foraging resemble those of adults. Sexual maturity is reached at roughly two to three years.

That slow schedule limits population recovery. Species that produce one dependent infant at long intervals cannot quickly replace adults lost to forest clearing or killing.

The IUCN lists the aye-aye as Endangered and considers the population to be decreasing. Forest conversion for agriculture, timber extraction and development removes and fragments habitat across Madagascar. Even where trees remain, deliberate killing can be a serious local threat.

Some Malagasy communities associate the aye-aye with harmful omens, though beliefs vary greatly from place to place and should not be treated as a single national tradition. In agricultural areas the animal may also be killed after feeding on coconuts, lychees or other crops. These pressures operate alongside a slow reproductive rate and an uncertain wild population size.

Protected areas hold aye-ayes in several regions, and conservation breeding has produced a small managed population outside Madagascar. The fossa, Madagascar's largest native carnivore, can prey on aye-ayes, but human activity is the dominant conservation problem. Protecting connected forest and reducing retaliatory killing matter more than simply proving the animal occurs at additional sites.

The aye-aye is a strepsirrhine primate and a relative of other lemurs, but its lineage separated early. It is the only living species in Daubentonia and Daubentoniidae. A larger relative, Daubentonia robusta, survived into the recent past before disappearing after people reached Madagascar.

Early European naturalists struggled to classify the living species because its incisors and gnawing behavior looked rodent-like. Anatomy and later genetic evidence placed it firmly among primates. The resemblance to a rodent is an example of convergent adaptation: similar feeding demands produced similar tools in animals with very different ancestry.

• Duke Lemur Center: Aye-aye
• IUCN Red List: Amazing Species — Aye-aye
• Animal Diversity Web: Daubentonia madagascariensis
• American Journal of Physical Anthropology: The aye-aye's pseudothumb
• Duke Lemur Center: Island of Evolution