Animal Diversity Web

Geographic Range

Chibchanomys orcesi is a highly endemic species, occurring only in Las Cajas Plateau in southern Ecuador. It has been captured in three locations in this region, which include the surrounding areas of Lake Luspa, Lake Llaviucu, and Lake Torreadora. The range size of this species is not known but it has only been found in Cajas National Park, which is about 285.44 km2 or 28,544 ha. (Barnett, 1997; Jenkins and Barnett, 1997; "Parque Nacional Cajas", 2015)

• Biogeographic Regions
• neotropical
  • native

Habitat

Chibchanomys orcesi lives in a páramo ecosystem, categorized by its high-altitude moorland vegetation. It occurs near rapidly flowing streams surrounded by grassy vegetation and shrubs and has been found at elevations between 3,100 to 4,000 m. Chibchanomys orcesi has been most frequently captured near clear, shallow streams, no greater than 40 cm deep, that were on average 1 m wide. The bottom consisted of coarse gravel, stones, and bedrock, interspersed with large boulders and a lack of aquatic vegetation. Of the five captured specimens from Barnett’s research, three were found within close proximity to waterfalls. (Barnett, 1997; Barnett, 1999)

• Habitat Regions
• tropical
• terrestrial
• freshwater

• Terrestrial Biomes
• savanna or grassland
• mountains

• Aquatic Biomes
• rivers and streams

• Other Habitat Features
• riparian

• Range elevation

  3,100 to 4,000 m

  to ft

Physical Description

Chibchanomys orcesi weighs anywhere from 35 to 41 g, the head and body combined measures about 103 to 107 mm in length, and the tail is slightly longer than the length of the head and body together at 108 to 122 mm. This species has soft, dense, and woolly pelage that is dark brownish grey on its dorsal side and light grey on its venter. The tail is greyish brown with abundant hairs that turn cream as it progresses to the tip, forming a tuft past the end of the tail. Their muzzle is light grey in adults and turns cream as individuals age. Chibchanomys orcesi have light brown noses, small ears hidden by their pelage, small eyes, a pronounced head, and long vibrissae that are silvery grey in color. They have three interdigital pads and two carpal pads on their manus; and stiff hairs on the edge of their metatarsal and digits on the hind legs. The claw of their fifth digit extends past the first interphalangeal junction of the fourth digit, while the claw of the first digit extends to the midpoint of the second digit. There is no information on sexual dimorphism of Las Cajas water mouse, however sexes in its subfamily look alike (Jenkins and Barnett, 1997; Poor, 2005)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• Sexual Dimorphism
• sexes alike

• Range mass

  35 to 41 g

  1.23 to 1.44 oz

Reproduction

There is no information available on the mating systems of Chibchanomys orcesi or its ichthyomyine relatives. However, members in its subfamily Sigmodontinae tend to have a promiscuous mating system. (Poor, 2005)

• Mating System
• polygynandrous (promiscuous)

There is no information available on the general reproductive behavior of Chibchanomys orcesi. Data on reproduction for its ichthyomyine relatives is sporatic and does not identify seasonal trends. However, these relatives have been recorded to have litter sizes of one to two offspring. (Voss, 1988)

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

There is no information available on the parental care of Chibchanomys orcesi or its ichthyomyine relatives. However, females in this species subfamily, Sigmodontinae, generally care for their young alone. They are viviparous, birthing altricial offspring in nests built out of plant material. The young then stay with their mother until weaned, which can take 5 to 30 days. (Poor, 2005)

It can be tentatively assumed that Chibchanomys orcesi may birth and raise their young in tunnel systems instead of nests, as mentioned in the Behavior section.

• Parental Investment
• altricial
• female parental care
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • protecting
    • female

Lifespan/Longevity

There is no information available on the lifespan/longevity of Chibchanomys orcesi. However, members in its subfamily Sigmodontinae do not live very long. The majority of Sigmodontines do not live past one year in the wild but some species have survived to five years in captivity. (Poor, 2005)

Behavior

In the wild, Chibchanomys orcesi is a solitary, semi-aquatic species, and little is known about its behavior. However, one individual was held captive for four months before release, providing time for observation. Through this, it was determined that Chibchanomys orcesi is nocturnal but was sometimes seen emerging for short periods in the daytime. It also created tunnels in addition to the artificial burrow provided, shedding light that this species may be semi-fossorial. (Barnett, 1997)

Phylogenetic relatives of Chibchanomys orcesi in the Genus Ichthyomys, have been recorded using small emergent objects to rest, feed and groom. It may be tentatively assumed that Chibchanomys orcesi employs these behaviors as well. (Barnett, 1997)

• Key Behaviors
• terricolous
• fossorial
• nocturnal
• motile
• sedentary
• solitary

Communication and Perception

The eyes of Chibchanomys orcesi are small and reduced. Instead, it has highly developed and stiff vibrissae that form a broad, arc-like array. Their trigeminal nerve is also enlarged in comparison to other rodents. The high development of their vibrissae and trigeminal nerve likely replaces vision in this species, allowing them to rely on tactile cues to navigate and perceive their environment. (Barnett, 1997; Jenkins and Barnett, 1997)

There is no information available on how this species communicates with others. However, members in its subfamily Sigmodontinae communicate through a variety of squeaking noises in addition to being able to detect and produce ultrasounds. Males also scent-mark their territories with urine and feces. (Poor, 2005)

• Communication Channels
• tactile
• acoustic

• Other Communication Modes
• scent marks

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

Food Habits

Chibchanomys orcesi preys primarily on aquatic invertebrates. Analysis of one individuals stomach content revealed larvae of Ephemeroptera and Trichoptera as well as fish scales and bones. When its preferred prey is scarce, Chibchanomys orcesi supplements its diet with small fish caught in streams. (Barnett, 1997; Barnett, 1999)

They use their highly developed vibrissae and forepaws to locate and capture their food, eating and manipulating it with their forepaws. The food handling behavior of Chibchanomys orcesi is similar to that of its relative Ichthyomys pittieri described by Voss et al. (1982). Observations of individuals has revealed they hunt for fish underwater and then take them to a separate location, like the tunnels mentioned above, to consume the fish. (Barnett, 1997; Barnett, 1999)

• Primary Diet
• carnivore
  • piscivore
  • insectivore

• Animal Foods
• fish
• insects

Predation

There is no information available on the predation of Chibchanomys orcesi. However, general predators of its subfamily Sigmodontinae include hawks, owls, snakes and carnivorous mammals. It should be noted that semiaquatic species of Sigmodontinae, like Chibchanomys orcesi, may avoid predation by diving into water. They may also avoid predation through use of their burrows and tunnels. (Poor, 2005)

Ecosystem Roles

There is little information on the ecosystem roles of Chibchanomys orcesi. However, they likely provide food for other animals mentioned in the Predation section. In addition, as an insectivore, Chibchanomys orcesi may control insect and aquatic invertebrate populations within their range. Through their tunnel digging, this species could also function as an ecosystem engineer.

Chibchanomys orcesi may be considered as an indicator species to determine ecosystem health in its geographic range. Its specific requirements for food and habitat, as well as its high endemism, could help ecologists in their conservation of páramo ecosystems. Changes in water quality may impact the aquatic invertebrates that Chibchanomys orcesi depends on, so declines in their population could be a good indication of aquatic and riparian health. However, its elusivity and low population density likely reduces its chances of being a viable indicator species. (Doskocil, 2020)

• Ecosystem Impact
• soil aeration

Economic Importance for Humans: Positive

There are no known positive effects of Chibchanomys orcesi on humans.

Economic Importance for Humans: Negative

There are no known adverse effects of Chibchanomys orcesi on humans.

Conservation Status

According to the IUCN database, the conservation status of Chibchanomys orcesi is data deficient. (Anderson, et al., 2019)

• IUCN Red List

  Data Deficient

Contributors

Gabrielle Krohn (author), University of Washington, Laura Prugh (editor), University of Washington, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Ministerio del Ambiente. 2015. "Parque Nacional Cajas" (On-line). Accessed June 26, 2021 at http://areasprotegidas.ambiente.gob.ec/en/areas-protegidas/cajas-national-park.

Anderson, R., M. Gómez-Laverde, M. Weksler. 2019. "Las Cajas Ichthyomine" (On-line). The IUCN Red List of Threatened Species. Accessed April 13, 2021 at https://www.iucnredlist.org/species/136775/22387119#bibliography.

Barnett, A. 1999. Small mammals of the Cajas Plateau, southern Ecuador: Ecology and natural history. Bulletin of the Florida Museum of Natural History, 42(4): 161-217. Accessed April 13, 2021 at https://www.floridamuseum.ufl.edu/wp-content/uploads/sites/35/2017/03/Vol-42-No-4.pdf.

Barnett, A. 1997. The ecology and natural history of a fishing mouse Chichanomys spec. nov. (Ichthyomyini: Muridae) from the Andes of southern Ecuador. International Journal of Mammalian Biology, 62: 43-52. Accessed April 13, 2021 at https://www.semanticscholar.org/paper/The-ecology-and-natural-history-of-a-fishing-mouse-Barnett/208fdb6ddd1e8c93c1f885efb53ba180d0e65ceb.

Doskocil, L. 2020. ""If Watersheds Spoke: A condition analysis of the Rio Tomebamba watershed in southern Ecuador using GIS analysis"" (On-line). Independent Study Project (ISP) Collection. Accessed April 13, 2021 at https://digitalcollections.sit.edu/isp_collection/3323/.

Jenkins, P., A. Barnett. 1997. A new species of water mouse, of the genus Chibchanomys (Rodentia, Muridae, Sigmodontinae) from Ecuador. Bulletin of The Natural History Museum, 63: 123-128. Accessed April 13, 2021 at http://www.rebeccashapley.com/akodon/reprint_pdfs/97Chibchanomys_orcesiNewSpeciesDescription.pdf.

Poor, A. 2005. "Sigmodontinae" (On-line). Animal Diversity Web. Accessed May 08, 2021 at https://animaldiversity.org/accounts/Sigmodontinae/.

Voss, R. 1988. Systematics and Ecology of Ichtyomyine rodents (Muroidea): Patterns of Morphological Evolution in a small Adaptive Radiation. Bulletin of The American Museum of Natural History, 188(2): 262-482. Accessed May 08, 2021 at https://digitallibrary.amnh.org/handle/2246/927.