Bare-tailed woolly opossums, Caluromys philander, are found in the rainforests of South America. The northern end of their range is delimited by the Venezuelan Andes and extends east along the South American coast line to north-central Brazil. It then continues south in an east-heading arc that rejoins the Atlantic Costal-forest around 15-degrees south latitude. Their range follows the coast to about 28-degrees south latitude, which is their apparent southern limit. Bare-tailed woolly opossums are found in the interior rainforest to about 55-degrees west longitude including parts of the Bolivian lowland rainforest. They range up to 1,800 m in elevation in primary and secondary growth forests and are also found on the island of Trinidad.

Biogeographic Regions: neotropical (Native )

Bare-tailed woolly opossums are medium-sized new-world arboreal opossums. Their weight ranges from 140 g to 390 g, with females being smaller than males. The average caloric intake for a 300 g individual is approximately 300 kJ/day. The body length, head to base of tail, is 160 mm to 279 mm and is always less than the length of the tail. The tail ranges from 250 mm to 405 mm in length. Outside ear length is 30 mm to 40 mm and hind foot length is 33 mm to 40 mm. The dental formula is I 5/4, C 1/1, P 3/3, M 4/4. The species has a distinctive post orbital process that can help distinguish it from other Neotropical marsupials.

The fur is generally soft and thick, with individuals in the lowlands having shorter coats than those in the uplands. The pelt has also been referred to as woolly, but all members of the genus Caluromys have a “woolly” pelt. The back is a reddish-brown with gray gradating in along the flanks. The belly is a yellowish-orange to gray color. The head is gray with three distinct dark-brown strips; one runs down the bridge of the muzzle from crown to nose and the other two extend from dark-brown eye-rings to the nose. The tail is furred for the first tenth to quarter of its length with a sharp demarcation between the furred and bare portions. The furless portion of the tail is cream to dark-gray or dark-brown in color, and is usually mottled with brown or white spots. Like many other Didelphidae the tail is also prehensile and helps with climbing, balancing, and grasping.

The eye-shine of bare-tailed woolly opossums is yellow and makes the eyes appear small. Females have a vestigial pouch, termed a marsupium, which is only present when they are carrying young. They also have seven mammae concealed by the marsupium.

Range mass: 140 to 390 g.

Average mass: 250 g.

Range length: 410 to 684 mm.

Sexual Dimorphism: male larger

• Terrestrial

Bare-tailed woolly opossums are highly arboreal. In studies of habitat use and partitioning they were rarely, if ever, found on the ground and seldom found in the understory. They are found in both primary- and secondary-growth evergreen tropical rainforests. They are known from damage to orchards and banana plantations. The preferred habitat of C. philander is not clear, and varies dependent upon season, geographic locality, food availability, and reproductive status. These animals show a preference for denser canopy within their habitat, likely for concealment from predators. They nest in tree hollows lined with leaves or in leaf-nests in the canopy.

Range elevation: 1,800 (high) m.

Habitat Regions: tropical ; terrestrial

Terrestrial Biomes: rainforest

Other Habitat Features: agricultural

C. philander is omnivorous; the diet is composed of approximately 25 percent arthropods and 75 percent fruit, nectar, and tree gum. Because of the seasonal availability of food, the diet varies greatly throughout the year. During the wet-season, fruits and arthropods are much more abundant, whereas during drier periods, flowers and gums are much more common. Because of this, bare-tailed woolly opossums have a long colon and well developed caecum to help with the processing of fibrous material. They eat ripe fruit, and are able to determine ripeness by non-visual queues as they feed on brightly-colored as well as cryptically-colored fruit.

Beetles and butterflies are the primary arthropods they prey upon, but other insects are taken. Two tree-species make up their primary diet; these are Eperua falcate, for nectar, and Symphonia globulifera, for fruit and nectar. Sixty-four percent of the fruit intake for bare-tailed woolly opossums in French Guiana came from five tree-species: Symphonia globulifera, Tapirira guianensis, Dacryodes nitren, Licania robusta and Humiriastrum subcrenatum. Eighty-three percent of the nectar diet came from three tree-species: Eperua falcate, Symphonia globulifera, and Norantea guianensis.

Animal Foods: mammals; insects

Plant Foods: fruit; nectar; sap or other plant fluids

Primary Diet: omnivore

The role of bare-tailed woolly opossums in tropical forests is not specifically known. They likely play host to many parasites. They also likely aid some small-seeded fruit-bearing tree-species in the dispersal of seeds and in the pollination of other species. They certainly are important for forest-floor species, as they knock down fruit from the overstory. One final role is that of a tasty protein morsel for many species of arboreal predators.

Ecosystem Impact: disperses seeds; pollinates

Species Used as Host:

• Unknown

Mutualist Species:

• Unknown

Commensal/Parasitic Species:

• Unknown

Given the moderately small size of bare-tailed woolly opossums, they are a prey item for many species. Arboreal nocturnal snakes and cats, such as Leopardus wiedii, are suggested as predators. Additionally, raptors, such as Morphnus guianensis, and the Strigidae are implicated.

Known Predators:

• margay cats (Leopardus wiedii)
• crested eagles (Morphnus guianensis)
• owls (Strigiformes)

Bare-tailed woolly opossums are generally quiet animals; they move as silently as possible through the tree branches. Most of their communication occurs during intraspecific encounters. In these cases they hiss in a manner similar to other opossums unless it is an encounter between a courting male and receptive female. They are also known to make clicking sounds and in the suckling young this is believed to strengthen the bond between mother and young. When taken by a predator, bare-tailed woolly opossums are known to give a distress scream.

Given the feeding habits of bare-tailed woolly opossums, it is likely that they have a developed sense of smell to help them find ripe fruit and flowers. The eyes and ears are also large and likely help them navigate the night-time forest and capture insects. These attributes make it likely that the animals also use some sorts of visual communication (such as body postures) and chemical communication (such as pheromones hypothesized to be important in inducing ovulation). Tactile communication is undoubtedly important during mating, as well as between a mother and her young.

Communication Channels: visual ; tactile ; acoustic ; chemical

Other Communication Modes: pheromones

Perception Channels: visual ; acoustic ; vibrations

Little is known about the lifespan of bare-tailed woolly opossums. Captive animals have lived for up to five years and animals of a minimum age of 31 to 41 months were captured in a mark-recapture study.

Range lifespan

Status: wild: 3.4 (high) years.

Range lifespan

Status: captivity: 5 (high) years.

Average lifespan

Status: captivity: 6.3 years.

The mating system of C. philander is little understood. Individuals are solitary except when males are courting females. Courtship may simply occur through chance meetings as the territories of many individual overlap.

Bare-tailed woolly opossums have up to 3 litters per year, but this is dependent upon resource availability. In one study, the breeding season was defined as beginning in September when there was an increase in the number of pregnant females concurrent with an increase in resource availability.

The average number of young varies greatly throughout the year dependent upon resource availability, habitat type, local conditions, as well as female age and mass. A female can have up to 7 young at once, but the average is 4.17 in the wild. There does not appear to be any additional cost to the female for large litters. It seems that the costs are borne by the young who are weaned at a smaller size in large litters than in small litters, indicating that regardless of litter size, female investment in any given litter is approximately constant.

Bare-tailed woolly opossums have a relatively short gestation period followed by an extended period of parental care. The gestation lasts only 24 days, and the young are born weighing less than 200 mg, with a length of 10 mm. This short time in utero is made up for by an extended period (up to 120 days) of pouch time. This period has two sub-periods, day 1 to 92, when the young are attached to the teat, and day 93 to weaning, when the young make short external excursions. The time in the pouch is followed by another 30 to 45 days in the mother’s nest. After this period the young leave the protection of the mother. The importance of leaving the maternal nest is demonstrated by the behavior of young in captivity. When young have not been removed after this period, they have been observed to cannibalize their mother.

Females reach sexual maturity around 270 days of age. The age of sexual maturity for males is not known. Little is known about the estrous cycle, but direct contact with males seems to induce fertility. This is hypothesized to result from pheromonal or behavioral cues from the male.

Breeding interval: In theory, a female could produce a new litter every 200 days.

Breeding season: The breeding of this species is aseasonal, but peaks matching resource availability

Range number of offspring: 1 to 7.

Average number of offspring: 4.17.

Average gestation period: 24 days.

Range weaning age: 103 to 120 days.

Range time to independence: 150 to 165 days.

Average age at sexual or reproductive maturity (female): 270 days.

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); induced ovulation ; fertilization ; viviparous

Average birth mass: 0.2 g.

Average gestation period: 24 days.

Average number of offspring: 4.5.

Average age at sexual or reproductive maturity (female)

Sex: female: 304 days.

In bare-tailed woolly opossums, care for the young is the singular responsibility of the female. After the short gestation period, the young are born quite undeveloped and altricial, requiring as much as 120 days in the marsupium to complete their development. Over the 144 to 159 days of care the mother protects and feeds them without any other assistance. Little is known about post dependence interactions.

Parental Investment: no parental involvement; altricial ; female parental care ; pre-fertilization (Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)

Bare-tailed woolly opossums are not listed as a species of conservation concern. They are small and able to adapt to various types of neotropical forests, are not involved in trade, or considered a pest to humans. However, as deforestation continues in neotropical regions, it is likely that this species will face growing pressure.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

There is some evidence that bare-tailed woolly opossums have done damage in banana plantations, but given their size and population density, this is very limited in scope.

Negative Impacts: crop pest

The only obvious economic benefit from bare-tailed woolly opossums has been in research. They have been used to study primitive gait patterns and for a limited amount of evolutionary investigation.

Positive Impacts: research and education