Aye-aye
Daubentonia madagascariensis

TAXONOMY

Suborder: Strepsirrhini
Infraorder: Chiromyiformes
Family: Daubentoniidae
Genus: Daubentonia
Species: D. madagascariensis

Other names: Aye-Aye; Fingerdyr eller aye-aye (Danish); Vingerdieren (Dutch); Aiai (Finnish); Fingertier (German); ahay, aiay, bekapaky, hay-hay, karakapaky (Malagasy); fingerdjur (Swedish)

Due to its specialized traits and distinctiveness from other primates, the aye-aye is included in its own family, genus and species. There has been much dispute as to where exactly to place the aye-aye taxonomically due to its odd conglomeration of traits.

MORPHOLOGY

The aye-aye is a distinctive and unique species and the largest nocturnal primate (Mittermeier et al. 1994; Simons 1995; Sterling 1995). It is dark in color with two layers of hair: longer, coarse black hair with white tips and shorter and softer off-white hair. The face of the aye-aye is pale in color with dark ring&s around the eyes and black ears (Mittermeier et al. 1994). In captivity, the average weight of an aye-aye male is 2.688 kg (5.926 lb) and females weigh 2.516 kg (5.547 lb) (Glander 1994). The aye-aye's body, excluding its tail, is approximately 319.5 mm for the males and 305 mm for the females. If the bushy tail is included, the aye-aye's body length more than doubles as its tail is longer than its body (Feistner & Sterling 1995). In addition, the aye-aye's tail has the longest hairs of any prosimian at over 9 in (22.5 cm) (Simons & Meyers 2001). There is little to no sexual dimorphism in the aye-aye (Feistner & Sterling 1995).

Photo: Tomas Junek

Perhaps the most marked trait of the aye-aye is a thin and elongated middle finger on each of its hands. This third digit is independent in movement from the other digits and is extremely versatile (Erickson 1994; Soligo 2005). The third digit's complete independence in movement serves two main purposes, tapping to find insects within cavities in wood and probing to find and remove larvae from those cavities (Milliken et al. 1991). This method of locating and extracting insect larval prey is called percussive foraging (Erickson 1994). Other uses of the elongated third digit include drinking liquids by quickly moving the digit back and forth between the aye-aye's mouth and the liquid, as well as grooming (Iwano 1991; Erickson 1994; Simons 1995). Movement of the third finger from the food source to the mouth can be very rapid and has been measured at 3.3 strokes per second (Iwano & Iwakawa 1988). The hand of the aye-aye is quite large for its body size. This aids in foraging, as only one hand is available to grip a perch while the other taps for prey. Large hands allow the aye-aye to grip with greater force and decrease its chance of falling (Soligo 2005).

Other unique morphological features of the aye-aye are its inguinal (located near the groin) mammary glands and nipples and its persistent oogenesis in which the female produces ova throughout her lifetime (Petter-Rousseaux & Bourlière 1965; Sterling 1993a). Also, the aye-aye possesses the largest brain among the prosimians (Erickson 1995). A final feature very rarely found in primates is the presence of a nictitating membrane (third eyelid), which moistens the eye when it becomes dry (Sterling 1993a; Sterling & Feistner 2000). This membrane may also protect the eye from wood debris when the aye-aye is gnawing on wood to extract larvae (Sterling 1993a).

The ears of the aye-aye are extremely large and moveable, presumably to assist in locating larvae in wood cavities through percussive foraging (Simons 1995). Percussive foraging may in fact rely on touch and not on auditory clues at all (Erickson 1994). The aye-aye possesses large, ever-growing incisors, which it uses to gnaw wood and to access the subsurface larvae it locates through tapping. This feature of ever-growing teeth is unique among primates (Simons 1995). It also uses its rodent-like teeth to gnaw at nuts and hard-shelled fruits (Sterling et al. 1994, Sterling 1994b).

The aye-aye moves quadrupedally, both walking and climbing. Climbing can be very rapid and agile leaping is also observed (Ancrenaz et al. 1994; Curtis & Feistner 1994). Descent down a tree trunk can be either headfirst or tailfirst (Ancrenaz et al. 1994). Aye-ayes possess a toilet-claw used in grooming and functional claws on other digits except the big toe (hallux). They are the only Old World primate to possess such functional claws (Sterling 1993a; Soligo & Müller 1999). The only other primates that have true claws are the Callitrichidae. The aye-aye claws appear to have redeveloped after having been lost by ancestral species (Soligo & Müller 1999). Aye-ayes have been known to survive in captivity for 24 years (Hakeem et al. 1996).

RANGE

The aye-aye is found exclusively in Madagascar. Situated to the southeast of Africa and separated from the continent by the 800 km-wide (497 mi) Mozambique Channel, the island of Madagascar is in the Indian Ocean and is the fourth largest island in the world (Swindler 2002). the aye-aye was believed to be extinct as recently as the mid-1900's, it now appears that the species has one of the largest distributions among non-human primates in Madagascar albeit at very low population densities (Sterling 1994a). Thus, the aye-aye range may not represent a continuous population distribution. They are found in the eastern rain forests of Madagascar from as far south as the Andohahela Reserve near the south coast to the northern end of the island at Ankarana Special Reserve (O'Connor et al. 1986; Hawkins et al. 1990). The west coast of Madagascar, long thought to be devoid of the aye-aye, is home to the species as far south as the Bemaraha Nature Reserve (Harcourt & Thornback 1990). The only area of Madagascar where the aye-aye is not found is the southwest of the island (Sterling 2003a).

Several artificial aye-aye populations have been established for conservation purposes and since 1986 a number of aye-ayes have been exported from Madagascar in an effort to establish captive breeding colonies. These efforts met with success in 1992 when the first captive-bred aye-aye was born to a colony at the Duke University Primate Center (Carroll & Haring 1994). Currently, there are over three dozen aye-ayes in captivity (http://www.isis.org). In 1966, aye-ayes were introduced on the island of Nosy Mangabe, located in the Bay of Antongil on the east coat of Madagascar. At that time, the island was designated a Special Reserve by the government of Madagascar and still serves as an important site of conservation (Constable et al. 1985).

HABITAT

Aye-ayes adapt well to different types of habitat, including those affected by people. Aye-ayes are typically found in Madagascar's eastern rainforest, deciduous forest, secondary littoral forest near the sea, degraded secondary forest and cultivated areas such as plantations (including those for the production of sugar cane, coconuts and cloves) (Pollock et al. 1985; Ganzhorn & Rabesoa 1986; Iwano & Iwakawa 1988; Harcourt & Thornback 1990; Ancrenaz et al. 1994; Andriamasimanana 1994). The aye-aye may also live in mangrove swamps and dry scrub forest (Tattersall 1982). Aye-ayes build their nests high in the crowns of trees and thus require habitats containing trees suitable for this purpose (Ancrenaz et al. 1994). Sightings of aye-ayes have also occurred at surprising distances from the nearest forest with one individual being sighted in savanna around 3 km (1.86 mi) from any type of forest (Hawkins et al. 1990). Because the aye-aye's distribution is spread all along the east coast of the island up to the northern areas and on the west coast, there are many differing temperatures and rainfall amounts within the aye-aye range. In the north of Madagascar, the aye-aye inhabits areas with windy, dry and warm winters and hot and humid summers. In the south of the island, the climate is less tropical and drier than in the eastern rainforests where it is rainy year-round (Donque cited in Jury 2003). There is no record of the aye-aye living in the spiny desert areas of the southwest of Madagascar (Sterling 2003). Aye-ayes can also live in a variety of altitudes, ranging from near sea level to as high as 1875 m (6151.57 ft) above sea level (Goodman & Ganzhorn 2004).

Aye-ayes have been studied in several locations, most significantly the island of Nosy Mangabe, located on the east coast of Madagascar in the Helodrano Antongila. Near Nosy Mangabe, records indicate that the average rainfall is 3326 mm (130.9 in) per year and temperatures range from 24.0 C (75.2 F) in July to 30.5 C (86.9 F) in January (Pollock et al. 1985). This introduced island population has been the site of studies by several researchers including Eleanor Sterling and Taizo Iwano. Other research has been conducted in the Mananara-Nord Biosphere Reserve just south of the Helodrano Antongila by Mina Andriamasimanana. In addition to these studies, several other field observations have taken place in addition to a number of captive studies.

ECOLOGY

Photo: David Haring

Aye-ayes eat a number of different types of food but it appears that primarily, they eat seeds, nectar, fungus, and insect larvae (Sterling et al. 1994). They are best described as omnivores whose food choice varies with habitat type and food availability. At Nosy Mangabe, 90% of the diet was composed of just four items, fruits, nectar, insect larvae, and growths (cankers) on the barks of trees (Sterling et al. 1994). When cultivated areas are near to or comprise the aye-aye habitat, however, other foods may enter the diet. At the Mananara-Nord Biosphere reserve on the mainland south of Nosy Mangabe, the main component of the aye-aye diet was the nectar of the traveller's tree (Ravenala madagascariensis). In the same reserve closer to a coconut plantation, however, the aye-aye staple was the coconut although this population still ate larvae as well (Ancrenaz et al. 1994). In a different study, also at Mananara-Nord, a male aye-aye ate, in order of preference, coconuts, larvae, and cankers on trees (Andriamasimanana 1994). Aye-ayes have also been observed eating ramy nuts (Canarium madagascariensis), a hard-shelled product of the ramy tree similar in form to a walnut, in addition to litchi and mango fruit (Petter & Petter 1967; Iwano & Iwakawa 1988).

The diet of the aye-aye also appears to change with the seasons as the availability of food changes. On Nosy Mangabe in the cold, wet season (mid-May to mid-August), reliance on cankers increases. This is in contrast to the rest of the year, during which aye-ayes rely more on seeds. Throughout the year, the aye-aye's reliance on insect larvae remained relatively constant (Sterling et al. 1994).

The aye-aye is nocturnal and sleeps in an arboreal nest during the day. Emergence from the nest for a start of activity may start as early as 30 minutes before sunset and the aye-aye may not return to a nest until after the sun rises in the morning (Ancrenaz et al. 1994). A male's nocturnal activity typically starts earlier than a female's and over the course of the nighttime activity, more than 50% of the aye-aye's time is spent moving. Other major activities undertaken by the aye-aye during its activity period are feeding, grooming and resting (Ancrenaz et al. 1994; Andriamasimanana 1994). Several times a night an aye-aye may self-groom in bouts lasting up to 30 minutes. This grooming may be performed with the aye-aye's hands, feet, and third digit, and the entire body is inspected. The longer the grooming session, the higher in the canopy the aye-aye will perch, ostensibly for safety (Ancrenaz et al. 1994). Nighttime activity is also punctuated by periods of rest in which the aye-aye remains sedentary but fully aware of its surroundings and is not asleep. These rest periods may last as long as two hours (Ancrenaz et al. 1994).

Photo: Tomas Junek

Aye-aye nests are typically oval-shaped and placed quite high in the crowns of, forks of and tangles in trees (Petter 1977; Ancrenaz et al. 1994). In one study, the height of such nests in trees was found to average 17.6 m (57.74 ft) (Sterling 1993a). There is an approximately 15 cm-wide (5.9 in) opening at one end of the nest (Petter 1977). Each aye-aye utilizes several nests and one aye-aye individual was observed using seven different nests in a four-week period. Sometimes nests are grouped close to one another and larger trees may contain several aye-aye nests (Ancrenaz et al. 1994). Different aye-ayes may use the same nest on different nights, and nests may be abandoned and then repaired and reused (Petter 1977; Andriamasimanana 1994; Mittermeier et al. 2006). In one study, a specific nest was observed to have been used by four individuals at different times (Sterling 1995). Typically, the species is observed to sleep one individual per nest per night; however, a pair of males has been observed sharing a nest in a single night (Sterling unpubl. data cited in Sterling 1993b).

The aye-aye home range has been measured on an island to vary from 1.26 km² (.49 mi²) to 2.15 km² (.83 mi²) for males and .317 km² (.12 mi²) to .395 km² (.15 mi²) for females (Sterling 1993b). Unrestrained by geography, the home ranges of aye-ayes may be significantly larger (Sterling pers. commun. cited in Andriamasimanana 1994). Either way, it does appear that the home range of the female is smaller than the male's. Nightly range length can range average from 1551.8 m (5091.21 ft) to 2256 m (7401.57 ft) for males and 1227.2 m (4026.25 ft) to 1528 m (5013.12 ft) for females. The home ranges of males may overlap those of other males and females. Home ranges of females have not been observed to overlap those of other females (Sterling 1993a; 1993b; 1995).

The only potential non-human predator for the aye-aye is the fossa (Cryptoprocta ferox), a large mammalian predator adapted for both arboreal and terrestrial movement (Petter 1977). Some human populations of Madagascar see aye-ayes as harbingers of bad luck and kill them on sight (Petter 1977). This belief makes humans the primary predator of the aye-aye.

SPECIAL NOTES

An extinct robust form of the aye-aye (Daubentonia robusta) once existed in the dry southwest of Madagascar, the only area where the extant form currently does not exist. This extinct form likely weighed between three and five times what Daubentonia madagascariensis weighs with a predicted average weight of around 13.5 kg (29.76 lbs) (Simons 1994). Some evidence exists as to the coexistence of this form with humans as several drilled incisors attributed to Daubentonia robusta have been found ostensibly for use as pendants of some sort. It remains unclear however as to whether or not human action contributed to the extinction of this species (MacPhee & Raholimavo 1988).

Content last modified: July 27, 2007

Written by Kurt Gron. Reviewed by Eleanor Sterling.

Cite this page as:
Gron KJ. 2007 July 27. Primate Factsheets: Aye-aye (Daubentonia madagascariensis) Taxonomy, Morphology, & Ecology . <http://pin.primate.wisc.edu/factsheets/entry/aye-aye/taxon>. Accessed 2015 January 30.