Aye-ayes

(Daubentoniidae)

Class Mammalia

Order Primates

Family Daubentoniidae

Thumbnail description
Medium-sized nocturnal and arboreal primates

Size
6 lb (2.7 kg); body and tail length average 16 in (40 cm) and 22 in (55 cm), respectively; body size of the extinct aye-aye is estimated at three times that of D. madagascariensis

Number of genera, species
1 genera; 1 extant species; 1 extinct species

Habitat
Rainforest, dry deciduous forest, and some cultivated areas

Conservation status
Endangered

Distribution
Madagascar

Evolution and systematics

The aye-aye (Daubentonia madagascariensis) is the only primate with a monotypic family, genus, and species. Because of their highly specialized characteristics, aye-ayes were initially difficult to classify and were lumped with several diverse groups until being firmly identified as prosimian in the mid-1800s. Recent genetic research shows that the aye-aye is not more closely related to one lemur family than another.

The taxonomy for this species is Daubentonia madagascariensis, (Gmelin, 1788), northwestern Madagascar.

Physical characteristics

Aye-ayes are the largest nocturnal primate. Their pelage consisted of two layers: the short, soft underlayer is light in color and thick on the back; the outer guard hairs are coarse, dark brown to black at the roots, and gray-white at the tips similar to a didelphid North American possum (Didelphis virginiana). Some aye-aye guard hairs have measured 7 in (18 cm). Fur above the eyes and on the throat is often light yellow or beige. Eyes are amber and are not frontally oriented. The body mass of males and females is not significantly different, with an average of 6 lb (2.7 kg). Body length averages at 16 in (40 cm), tail length at 22 in (55 cm). The tail is very bushy, more like a fox, than a primate. The ears are bare, flexible, and very large: 4 in (10 cm) length by 2.8 in (7 cm) width, probably the largest for the body size of any primate. The evergrowing incisors have enamel on the buccal side only, with a long dental gap before the molars, like a rodent, not a primate. The molars are flat and wear down quickly. Legs and arms are about the same length and aye-ayes walk on all fours. The third and fourth fingers of aye-ayes are elongated and the last knuckle on the middle digit has a ball and socket joint, allowing rotation. The female mammary glands are located iguanally, between her legs, not under her arms as seen in other primates. Aye-ayes have a nictitating membrane, a character shared with reptiles and birds but few other mammals. The male aye-aye has a penis bone that is 1.2 in (3 cm). Aye-ayes have the largest brain to body weight ratio of any prosimian. The isolated incisors and the arrangement of hand bones for percussive foraging suggest the robust extinct aye-aye (D. robusta) had a similar locomotion and lifestyle to the living smaller species.

Distribution

On Madagascar in forested regions from north (Marojejy National Park, Sambava) to south (Andohahela National Park, Tolagnaro, and throughout the humid rain forest in the east from the coast (Mananara Nord National Park, Manombo Reserve) to the mountains (Andrigitra National Park, Ranomafana National Park). In the west aye-ayes have been sighted in isolated localities, namely Tsiombikibo Forest, Tsingy of Bemaraha National Park and Kirindy Forest. The extinct species was found only in the southwest and south central region of Madagascar.

Habitat

The smaller living species is found in Madagascar in low and mid-altitude rainforest, dry deciduous forests, and some cultivated areas, particularly coconut and lychee plantations. The extinct aye-aye foraged in gallery and deciduous dry forests in the southwest and south-central region of Madagascar.

Behavior

Aye-ayes forage primarily alone. However, when a female is in estrus, she is followed by up to six males. Foraging associations are occasionally observed in the wild between two adult males, adult and young males, and adult males and females. Male home ranges (300–530 acres; 120–215 ha) overlap greatly with one another, while female home ranges (77–100 acres; 31–41 ha) do not overlap with other female

ranges. The average nightly path length of radio-collared females is 4,270 ft (1,300 m) with a maximum of 6,000 ft (1,830 m). The average nightly path length of males is 7,380 ft (2,250 m) with a maximum of 14,400 ft (4,390 m). These are the longest path lengths recorded for any nocturnal primate, and is especially remarkable considering the steep and wet terrain. Locomotion is by four-legged walking, climbing, and jumping; aye-ayes spend 25% of time walking on the ground. The mean height during travel is 23 ft (7 m) and the mean height during feeding is 43 ft (13 m). Aye-ayes are one of the top three terrestrial lemurs (ring-tailed lemurs, greater bamboo lemurs, and aye-ayes all spend a quarter to a third of their time on the ground). Aye-ayes sleep solitarily during the day in round nests about 72 ft (22 m) high in large trees with many vines; the round nests have one entrance and are constructed of branches with many fresh leaves. None of these nests is occupied by more than one individual on the same day, although nests may be serially occupied by other individuals. For example, one male serially shared nests with four other study animals, both males and females. Aye-ayes give up to 15 different vocalizations, including a contact "eep" call, an aggressive "aack" spacing call to other aye-ayes, "plea" calls

given by females in estrus, a "fishing reel" call given when animals are feeding, a "sneeze alarm" call, a "hai-hai" alarm call (a pulsed snit cry when individuals are fighting over food), and a begging "bird call" given by young aye-ayes wanting to feed with older animals. Females scentmark frequently using both urine and anogenital rubbing for 10 days before and the three days of estrus.

Feeding ecology and diet

Aye-ayes use their specialized anterior teeth and middle finger to harvest three main food sources—insect larvae from dead trees, inside nutmeat of seeds from the giant Canarium tree (Burseraceae family) and cankerous fungus growing on Intsia (Fabaceae family) trees. The fourth component of the diet is nectar from Traveller's palm (Ravenala madagascariensis) flowers. Ants were occasionally eaten. Using their evergrowing incisors to open the hard exterior of the seed, aye-ayes then scrape the interior out of the Canarium or coconut with their middle finger. Canarium seeds are 60% fat. Using the large ears to listen to dead wood, the aye-aye tap

to determine the location of the larvae, then gnaw open the beetle canals, emerge and rotate their long, thin, mobile fingertip to snag the beetle inside the log and pull it out. The insect larva were from cerambicid, scarab, and other beetle larvae that consume dead wood. These large larvae could weigh 0.2 oz (5 g) and are high in protein (44–70%) and fat (33–44%).

Reproductive biology

Aye-ayes are a polygynous group that sleep and forage solitarily, and in contrast to all other lemurs, mating can occur in different months of the year (October, February, December, May). Ten days prior to full estrus, as determined by genital swelling, females increase scent-marking frequency and often visit nests occupied by males, a behavior not seen outside the mating season. During the three days of estrus, females call repeatedly, starting well before dusk. Up to six males surround the calling female, with the males engaging in agonistic chases and biting. Eventually one male will copulate with the female, maintaining hold of the female for about

an hour. The pair are suspended by their back feet from a branch during the long copulation. After copulating, females travel quickly 1,640–1,970 ft (500–600 m) and call again. Females mate with more than one male on the first day. The gestation is 4–5 months. The infant remains in a nest with the mother for the first weeks, and lactation continues for two years. Age at first birth is 36–48 months, with an interbirth interval of 24–36 months. Only one offspring is born at one time.

Conservation status

Endangered. Hunting and loss of habitat due to logging and crop cultivation are main concerns.

Significance to humans

Because of their odd appearance, aye-ayes fall victim to superstitious fear in the north of Madagascar and are often killed on sight—one belief is that upon seeing an aye-aye, a member of the observer's family will die unless the animal is killed. Subfossil incisor teeth of D. robusta had symmetrical holes, perhaps for hanging as necklaces or amulets. Aye-ayes carry no economic importance except as crop raiders in coconut plantations.

Resources

Books

Garbutt, N. Mammals of Madagascar. Sussex, UK: Pica Press and Yale University Press, 1999.

Mittermeier, R. A., I. Tattersall, W. R. Konstant, D. Meyers, and R. B. Mast. Lemurs of Madagascar. Washington, DC: Conservation International, 1994.

Rowe, N. Pictorial Guide to the Primates. East Hampton, NY: Pogonias Press, 1996.

Simons, E. L. "Lemurs: Old and New." In Natural Change and Human Impact in Madagascar, edited by S. M. Goodman and B. D. Patterson. Washington, DC: Smithsonian Institution Press, 1997.

Sterling, E. J. "Patterns of Range Use and Social Organization in Aye-ayes (Daubentonia madagascariensis) on Nosy Mangabe." In Lemur Social Systems and their Ecological Basis, edited by P.M. Kappeler and J. U. Ganzhorn. New York: Plenum Press, 1993.

Periodicals

Erickson, C. J. "Percussive foraging in the aye-aye (Daubentonia madagascariensis)." Animal Behavior 41 (1991): 793–801.

Feistner, A. T. C., and E. J. Sterling, eds. "The aye-aye: Madagascar's most puzzling primate." Folia Primatologica 62 (1994).

Ganzhorn, J. U. "The aye-aye found in the eastern rain forest of Madagascar." Folia Primatologica 46 (1986): 125–126.

Iwano, T., and C. Iwakawa. "Feeding behaviour of the aye-aye (Daubentonia madagascariensis) on nuts of ramy (Canarium madagascariensis)." Folia Primatologica 50 (1988): 136–142.

Simons, E. L. "The discovery of the western aye-aye." Lemur News 1, no. 6 (1992).

Sterling, E. J. "Timing of reproduction in aye-ayes (Daubentonia madagascariensis) in Madagascar." American Journal of Primatology 27 (1992): 59–60.

Yoder A. D., M. Cartmill, M. Ruvolo, K. Smith, and R. Vagalys. "Ancient single origin for Malagasy primates." Proceedings of the National Academy Sciences 93 (1996): 5122–5126.

Organizations

Duke University Primate Center. Lemur Lane, Durham, NC 27705. Phone: (919) 489-3364. Web site: <http://www.duke.edu/web/primate>

Patricia Wright, PhD