AnimaliaHighest rank in taxonomy. Groups all life into domains: Animalia, Plantae, Fungi, etc.IUCN LCInternational Union for Conservation of Nature — the world authority on species extinction risk, using standardized criteria. — Least Concern — widespread and abundant; not at immediate risk of extinction.In ProgressCurrent stage of this record in the editorial review workflow. Recent Sighting
Rheomys thomasi
Thomas's Water Mouse
Thomas, 1906
Detailed Texts Multi-lang
A rare, small semi-aquatic rodent characterized by a sleek, waterproof coat and specialized morphological traits for life in high-altitude mountain streams.
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Anonymous Curator
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Under Review
Other Names (Global)Regional and multilingual names used for this species across different countries and languages.
Ratón acuático de ThomasThomas's water mouse
TaxonomyBiological classification ranks placing this species within the tree of life, from Kingdom down to Genus.
PhylumRank below Kingdom. Groups organisms sharing a fundamental body plan (e.g., Chordata = vertebrates and some invertebrates).Chordata
ClassRank below Phylum. Subdivides by structural traits (e.g., Mammalia, Aves, Reptilia, Insecta).Mammalia
OrderRank below Class. Groups related families sharing common ancestry (e.g., Carnivora, Primates).Rodentia
FamilyRank below Order. Groups closely related genera (e.g., Felidae = cats, Canidae = dogs).Cricetidae
GenusRank just above Species. The first word in the two-part binomial scientific name.Rheomys
Taxonomic AuthorityThe scientist who first formally described and published this species, followed by the year of publication.Thomas, 1906
Record Completeness
93%Coming soon
Ecology & StatusHow this species lives: habitat preferences, diet, behavior, population status, and role in its ecosystem.
OriginWhether the species is native (evolved here), endemic (found only here), or introduced by human activity.
Native
Population TrendDirection of change in population size over time: increasing, stable, decreasing, or unknown.
Unknown
Breeding SeasonTime of year when this species typically reproduces or flowers.
Year Round
Trophic RolePosition in the food chain: producer, herbivore, carnivore, omnivore, decomposer, or parasite.
Carnivore
Recent SightingsWhether this species has been observed in the wild in Costa Rica within recent years.
Yes
Habitat SummaryOverview of the specific ecosystems and environments where this species is found in Costa Rica. Multi-lang
Restricted to cold, clear, high-altitude streams and surrounding riparian vegetation in the mountainous regions of southern Mexico and Guatemala.BehaviourDaily activity patterns, movement, territory use, foraging style, and seasonal behavioral changes. Multi-lang
Crepuscular and nocturnal. They are solitary and maintain territories along small mountain streams.Social ActivitySocial structure: whether the species is solitary, paired, or colonial; hierarchy and communication. Multi-lang
Generally solitary behavior.Feeding GuildWhat the species eats, how it forages or hunts, and its role as a consumer in the food web. Multi-lang
Aquatic predator.Trophic Chain DetailsSpecific interactions in local food webs: prey species, predators, competitors, and scavengers. Multi-lang
Carnivorous; hunts aquatic insects, small fish, and crustaceans by diving and scouring the stream bed.Reproductive BehaviourMating strategies, courtship displays, nesting or spawning behavior, and parental care. Multi-lang
Little is known, but it is believed they nest in protected crevices near the water line.Physical Measures
Length (cm)
8.0 - 12.0 cm
Weight (Grams)
25 g - 45 g
Offspring per cycleTypical number of young (live births, eggs, or seeds) produced by one adult in a single reproductive event or breeding season.1 - 3
Sexual DimorphismObservable physical differences between males and females of the same species (e.g., size, coloration, features).No
Lifespan
Sexual MaturityAge at which the individual becomes capable of reproducing for the first time.
3 - 5 Months
Gestation / IncubationDuration from fertilization to birth (mammals) or to hatching (egg-laying species).
25 - 30
Lifespan EstimatedExpected duration of life from birth to natural death under wild conditions.
Males1 - 2 Years
Females1 - 2 Years
Evolutionary AdaptationsInherited traits and behaviors that improve the species' survival and reproduction in its specific environment. Multi-lang
Possesses a dense, hydrophobic underfur that traps air for insulation while submerged, essential for survival in near-freezing water.
Main ThreatsDocumented pressures reducing the population: habitat loss, hunting, disease, climate change, and invasive species. Multi-lang
Highly susceptible to anthropogenic disturbances of stream health, including sedimentation and chemical pollution from agriculture.
Interesting FactsSurprising or notable facts that highlight what makes this species unique or ecologically important. Multi-lang
Due to their highly specialized niche, they act as sensitive bioindicators of stream water quality and ecosystem health in high-altitude regions.