Avahi occidentalis

Geographic Range

Western woolly lemurs are found only in a restricted region in Madagascar. They are found north and east of the Betsiboka river from the Ankarafantsika Reserve to the Bay of Narinda. In addition, enclaves can be found further north on the island, in the Manongarivo Special Reserve.

• Biogeographic Regions
• ethiopian ethiopian
  • native native

• Other Geographic Terms
• island endemic island endemic

Habitat

Western woolly lemurs are found in both tropical dry deciduous and secondary forests, occasionally reaching high population densities. They are typically observed in the forest canopy.

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest

Physical Description

Western woolly lemur head-body length ranges from 25 to 29 centimeters, with the tail significantly longer at 31 to 37 centimeters. Total length ranges from 56 to 65 centimeters. This makes western woolly lemurs the smallest species of Indriidae . The dorsal fur is dense and tightly curled, hence the common name "woolly lemurs." Body coloration is light or medium grey, with some individuals exhibiting brown or olive flecks. The fur lightens in color as it approaches the rear of the animal. The tail is normally the same shade of grey as the body, but some animals have been noted to have red tails. Fur on the face, throat, and cheeks is white, distinguishing the species from Avahi laniger , which has brown fur in these areas.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Reproduction

Western woolly lemurs are monogamous. Breeding pairs live together with their offspring year-round.

• Mating System
• monogamous monogamous

Like all other indriids , western woolly lemurs give birth to one offspring at a time. Breeding is seasonal, occurring from April to May, with birthing following 4 to 5 months later in August and September after a gestation period of 120 to 150 days.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous viviparous

Mothers initially carry infants on the ventral side, or belly, then later switch infants to their dorsal side. Young woolly lemurs stay with their parents for up to two years following birth.

• Parental Investment
• altricial altricial
• female parental care female parental care
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• extended period of juvenile learning

Lifespan/Longevity

Not much is known about the western woolly lemur's lifespan. Captured individuals have never survived for longer than a few days; the cause is hypothesized to be its highly selective folivorous diet.

Behavior

Western woolly lemurs live in family groups of 2 to 5 individuals; 3 is the most common number seen. Groups consist of a monogamous breeding pair with their young of up to two years. Family groups range around home territories of 1 to 2 hectares. Territory defense is rather lackluster, especially compared to closely related woolly lemurs in the eastern rain forests, Avahi laniger - western woolly lemurs tolerate much greater overlap between groups.

The western woolly lemurs, along with the other members of the genus Avahi , are the only nocturnal indriids . They are active at night and inactive during the day, although even at night, western woolly lemurs spend much of their time resting. Feeding is most common in the two hours after dusk and the two hours before dawn. Their seeming indolence is thought to be because their folivorous diet is not as energy-rich as other sources of food.

Like all indriids , western woolly lemurs are vertical clingers and leapers. Leaps have a mean length of 1.51 meters. Travel occurs most often during the first and last hour of the night. Family groups can cover large distances when traveling.

• Key Behaviors
• arboreal arboreal
• saltatorial saltatorial
• nocturnal nocturnal
• motile motile
• sedentary sedentary
• social social

Home Range

Not much is known about the home range of A. occidentalis . Territories are generally 1 to 2 hectares and are not strictly defended, in contrast to Avahi laniger .

Communication and Perception

Both sexes have scent glands on the neck that are used in olfactory communication. In addition to scent markings, the western woolly lemur uses several calls to communicate with its own group and with others. These include infant calls, which are plaintive, whistle-like noises used by the infant to attract its mother's attention. It also includes distant communication calls: a series of modulated, prolonged, high-pitched whistles. This call is used to help communicate territory borders and the receiver will reply with the same call. An alarm call varies with level of disturbance. In response to mild disturbance, it begins as a faint grunting sound, followed by a snorting sound. When highly disturbed, individuals use a loud, trembling call that sounds like "Ava Hy", hence the genus name. A cohesion call is a sudden, high-pitched call sounded when an individual is separated from another by 50 meters after an alarm.

• Communication Channels
• acoustic acoustic
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Western woolly lemurs are highly selective folivores, only parts of the leaf blade are fed upon, never the midrib or the petiole. Targeted leaves are usually immature, although mature leaves will also be consumed. After studying leaves eaten by individuals, it was found that none contained a significant amount of alkaloids. At the same time, the species of plants consumed generally exhibit protein and sugar rich leaves. Individuals are very selective about their leaves; more than 20 species of plant have been reported as food sources, many of which are not commonly found in the forests of western Madagascar. Feeding, along with most other activities, occurs in the canopy, at heights ranging from 2 to 9 meters. Interestingly, when sharing habitat with Lepilemur species , which are also folivorous, A. occidentalis generally prevents Lepilemur from accessing better-quality food sources.

• Primary Diet
• herbivore herbivore
  • folivore folivore

• Plant Foods
• leaves

Predation

The closely related A. laniger is a favored food of Malagasy raptors. It is reasonable to assume that the same raptors also prey on A. occidentalis . Their pelage acts as camouflage, blending into the trees it clings from.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Western woolly lemurs are most likely preyed upon by the raptors that co-occur with them. Where they co-occur with Lepilemur species, they restrict access to quality food resources for these Lepilemur species.

Little is known about lemur endoparasites, and, indeed, lemur parasites in general: the last great period of effort in naming and describing lemur parasites began around 1950 and petered out around the 1960's. Since then, studies have tended to focus more on the impact of parasites on their host species than the parasites themselves; A. occidentalis is no exception. Note: of the species listed, only Dipetalonema petteri has been found in A. occidentalis ; the remainder were described in the closely related A. laniger and, due to the at-times questionable relationship between the two species, it is possible that they infect A. occidentalis as well.

An interesting note about the worm Dipetalonema petteri : although it was found in multiple necropsies of many lemur species, no males have ever been noted - only female worms have been recovered. The reasons behind this remain unknown.

Economic Importance for Humans: Positive

Individually, western woolly lemurs have negligible positive impacts for humans, but the fascinating highly endemic Malagasy fauna, including other lemur species, are a major ecotourist attraction.

• Positive Impacts
• ecotourism ecotourism

Economic Importance for Humans: Negative

Western woolly lemurs have no negative impact on humans.

Conservation Status

The IUCN lists A. occidentalis as endangered. Factors include its small range, fragmented populations, and recent declines in habitat and population. The most significant threat to the species is habitat destruction - mostly yearly burning of forest in order to generate new grazing land for cattle. It is also hunted to some degree.

Other Comments

Western woolly lemurs have variously been listed as the same species as the woolly lemur, Avahi laniger , considered a subspecies of A. laniger , or its own separate species. Most recently, it has been named a separate species, with the name Avahi occidentalis .

Additional Links

Encyclopedia of Life

Contributors

Andrew Yu (author), Yale University, Eric Sargis (editor), Yale University, Rachel Racicot (editor), Yale University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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Thalmann, U., T. Geissmann. 2000. Distribution and Geographic Variation in the Western Woolly Lemur (Avahi occidentalis) with Description of a New Species (A. unicolor). International Journal of Primatology , 21(6): 915-941.

Thalmann, U. 2001. Food Resource Characteristics in Two Nocturnal Lemurs with Different Social Behavior: Avahi occidentalis and Lepilemur edwardsi. International Journal of Primatology , 22(2): 287-324.

Warren, R. 1997. Habitat Use and Support Preference of Two Free-Ranging Saltatory Lemurs (Lepilemur edwardsi and Avahi occidentalis). Journal of Zoology , 241(2): 325-341.

2007. "Western Woolly Lemur" (On-line). The Primata. Accessed August 16, 2012 at http://www.theprimata.com/avahi_occidentalis.html .