By Karen Gerde
Geographic Range
Silky shrew opossums, Caenolestes fuliginosus, live in the Andes, at altitudes ranging from 1,500 to 4,000 m. Their range is distributed throughout western Venezuela, north and west Columbia, and Ecuador. ("Shrew opossum (Caenolestes fuliginosus)", 2004; "Shrew opossum", 2004; Lunde and Pacheco, 2003)
Biogeographic Regions:
neotropical 
(native ).
Habitat
(4920 to 13120 ft)
This species lives in the alpine forests and meadows of the Andes. These are cool, wet, heavy vegetation areas, where they can build tunnels in surface vegetation for travel. ("Shrew opossum (Caenolestes fuliginosus)", 2004)
These animals are found in the following types of habitat:
tropical ; terrestrial .
Terrestrial Biomes:
mountains .
Physical Description
(0.58 to 1.44 oz)
(3.66 to 5.47 in)
Caenolestes fuliginosus is sexually dimorphic. The mass of females ranges from 16.5 to 22.4 g, and the mass of males ranges from 25 to 40.8 g. The head and body length is between 90 and 135 mm; including the tail, their length ranges from 93 to 139 mm. Pelage contains hairs with different textures, which creates an uneven appearance. The fur is soft and thick, with dark brown to almost black dorsally, and noticeably lighter fur on the ventrum. The non-prehensile tail is the same color as the dorsal pelage and is almost naked. The head is elongated (similar to that of a rat), with small eyes, and ears extending above the fur line. Upper and lower lip flaps are present. Feet each have five digits. On the forefeet, the two outer digits have blunt claws, and the inner three digits have sharp curved nails. Digits on the hind feet display curved claws except for the inner digit. The inner digit on both hind feet is small with a small nail. ("Shrew opossum (Caenolestes fuliginosus)", 2004; "Shrew opossum", 2004; Patterson and Gallardo, 1987)
Some key physical features:
endothermic ; homoiothermic; bilateral symmetry .
Sexual dimorphism: male larger.
Reproduction
Breeding is predicted to occur once yearly.
Breeding is likely to take place in early July, although males may be capable of breeding year round.
Not much is known about the mating system of silky shrew opossums other than the fact that these animals reproduce sexually. Females are predicted to be reproductively active only in the summer, because all female Rhyncholestes (another genus of shrew opossum in the family Caenolestidae) captured in the spring had unperforated vaginae and showed no signs of pregnancy or lactation. The extreme sexual dimorphism suggests that these animals may be polygynous. (Patterson and Gallardo, 1987)
Females are reproductively active only in the summer. August has been the only time of year when suckling young have been captured. However, male shrew opossums are capable of breeding all year long, based on the position of their testes. Because silky shrew opossums have two pairs of mammae, it is predicted that they could have between 1 and 6 offspring in a litter, based on the pattern of lactating female teat development. However, no actual observations of litters have been reported. ("Shrew opossum (Caenolestes fuliginosus)", 2004; Patterson and Gallardo, 1987)
Key reproductive features:
iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous .
Observations of maternal behavior have not been made directly. It is predicted that females utilize a form of nesting during the reproductive season based on the fact that few or no females have been trapped anytime soon after giving birth, and no attached offspring have been found. The marsupium in this species is confined to juveniles. Offspring in marsupials are always altricial, because the lack of placentation does not allow complete development of the young prior to birth.
In the genus Rhynolestes, also in the family Caenolestidae, there have been suspected "family groups" captured. In four consecutive nights one adult male, one adult female, and two juveniles were captured in the same trap in the same location that had not been washed between captures. If this in fact was a family group, it could suggest both male and female parental care. (Patterson and Gallardo, 1987)
Parental investment:
altricial ; pre-fertilization (provisioning, protecting: female); pre-hatching/birth (provisioning: female, protecting: female); pre-weaning/fledging (provisioning: female, protecting: female); pre-independence (provisioning: female, protecting: female).
Lifespan/Longevity
Information does not exist on the lifespan of C. fuliginosus, partly because of the inaccessible and rugged habitat in which they live. Given their small size, it is not likely that they live many years. ("Shrew opossum", 2004)
Behavior
Little is known about the behavior of silky shrew opossums. They run and live along tunnels in the surface vegetation that they create. These animals have low recapture frequencies, therefore it is predicted that the can become “trap-shy", making it difficult to determine an individual’s territory size. The majority of the captures made in the Caenolestidae family occur overnight, therefore leading researchers to suggest they are primarily nocturnal. ("Shrew opossum (Caenolestes fuliginosus)", 2004; Patterson and Gallardo, 1987)
Home Range
Home range size is not known for these animals.
Communication and Perception
These animals have poor sight, but well-developed senses of smell and hearing, as well as sensitive and long vibrissae. They most likely use their well-developed senses to locate their prey in the evening and at night. However, because of their sensitive hearing, they most likely communicate with each other through sound, and identify each other through their unique sense of smell. ("Shrew opossum (Caenolestes fuliginosus)", 2004; "Shrew opossum", 2004)
Perception channels:
visual ; infrared/heat ; tactile ; acoustic ; vibrations ; chemical .
Food Habits
Silky shrew opossums are mainly insectivorous, and can use their incisors to probe in search of insects. However, they are also known to hunt and kill other small vertebrates and earthworms for food. Even small seeds have been found in the digestive tracts. They hunt in the early evening and at night; they are mostly nocturnal. They use their long vibrissae (whiskers) and well-developed sense of hearing to locate their prey. ("Shrew opossum (Caenolestes fuliginosus)", 2004; "Shrew opossum", 2004; Patterson and Gallardo, 1987)
Primary Diet:
carnivore (insectivore ).
Animal Foods:
mammals; insects; terrestrial worms.
Plant Foods:
seeds, grains, and nuts.
Predation
Any larger animal living in the Andes that has access to C. fuliginosus terrain could be a possible predator. To protect themselves, silky shrew opossums are cryptically colored, and their keen sense of hearing and smell allow them a chance to quickly run for safety. ("Shrew opossum (Caenolestes fuliginosus)", 2004; "Shrew opossum", 2004)
Anti-predator adaptations::
cryptic .
Ecosystem Roles
The full effects these animals have on their ecosystems are still mostly unknown. However, they do impact the animals they prey on (insects and worms), as well as the animals that prey on them, but the extent of this impact is still not fully understood. ("Shrew opossum (Caenolestes fuliginosus)", 2004; "Shrew opossum", 2004)
- Ticks/mites
Economic Importance for Humans: Negative
No substantially negative impacts to humans have been discovered from this animal. ("Shrew opossum (Caenolestes fuliginosus)", 2004)
Economic Importance for Humans: Positive
These animals have little effect on humans, and live in a completely different habitat. However, in human’s search for cures, some research has started to take place in this family, Caenolestidae. The breast cancer BRCA1 protein is being studied in many marsupials, including C. fuliginosus. (Ramirez et al., 2004)
Ways that people benefit from these animals:
research and education.
Conservation Status
IUCN Red List: [link]:
Lower Risk - Least Concern.
US Federal List: [link]:
No special status.
CITES: [link]:
No special status.
The conservation status of this species is unknown, mainly because of the inaccessible and rugged habitat it lives in, the fact that not many specimens have been captured, and that little is known about its life span and environmental interactions. It was once considered rare, but more recent studies have started suggesting otherwise. ("Shrew opossum", 2004)
Other Comments
With more information on and more observations of C. fuliginosus, information such as their life span, reproductive behaviors, and their positive and negative impacts on humans can be determined. This information can also help make decisions determining their conservation status, as well as future research possibilities.
Contributors
Karen Gerde (author), University of Alaska, Fairbanks. Link Olson (editor, instructor), University of Alaska, Fairbanks.
Nancy Shefferly (editor), Animal Diversity Web Staff.
