User:Trish le/Mountain beaver

Mountain Beaver

Mountain beavers are found in the Cascade Mountains of British Columbia and southward to include the rest of the Cascade Range in the United States, the Olympic Mountains and Coast Ranges of Washington and Oregon, plus the Klamath Mountains, and the Sierra Nevada mountain range, Point Arena and Pt. Reyes of California and extreme western Nevada. They range from sea level to the tree line. They can be found in both deciduous and coniferous forests, but throughout most of the range they appear to prefer the former. These animals are physiologically limited to moist microenvironments, with most subspecies occurring only in regions with minimal snowfall and cool winters. They do not appear to be able to conserve body heat or warmth as efficiently as other rodents, nor do they hibernate. Due to their poor thermoregulation skills, they have not migrated outside of North America to avoid heat stress.

The breeding season is between January and March, with two or three young born annually from February to April. The ovulation period lasts a few weeks while gestation occurs for a month. The young are born hairless, pink, and blind. They are weaned at 6-8 weeks and leave the burrow soon after. Lifespans are 5 to 10 years – fairly long for rodents. They are not social, though home ranges can overlap.

Characteristics

Mountain beavers are gray or brown, but their fur can range from slightly more reddish to more blackish depending on subspecies, with a light patch under each ear. The animals have distinctively short tails. Adults weigh about 500–900 g (18–32 oz), with a few specimens topping 1,000 g (35 oz). Total length is about 30–50 cm (12–20 in), with a tail length of 1–4 cm (0.39–1.57 in). Their superficial similarity with true beavers reflects only their relatively large size (for rodents), strong odor, preference for living in extremely watery / moist habitats, and propensity to consume tree seedlings as food – mountain beavers do not fell adult trees (though such trees may be killed by "girdling"), build dams, live in lodges, or communicate by tail slappings. They are predominantly nocturnal in above ground activities. They are known to climb trees a few meters to acquire food in the form of branches and leaves, but otherwise their diet consists mostly of ferns, especially species which are toxic to other animals.

The skull is protrogomorphous; it has no specialized attachments for the masseter muscles as seen in other rodents. It is flattened and lacks a postorbital process. The baculum is thin and distinctly forked. The penis is about 4.5 cm (1.8 in) in length. The male does not have a true scrotum, but the testes move into a position called semiscrotal during the breeding season.

Mountain beavers have an unusual projection on each molar and premolar tooth, which is unique among mammals and allows for easy identification of teeth. This projection points toward the cheek on the upper tooth row, but points toward the tongue on the lower. The cheek teeth lack the complex folds of other rodents and instead consist of single basins. They are hypsodont and ever-growing. Two upper and one lower premolars are present, along with all the molars, giving a dental formula of 1.0.2.31.0.1.3

Mountain beavers cannot produce concentrated urine. They are thought to be physiologically restricted to the temperate rain forest regions of the North American Pacific coast and moist microenvironments inland due to their inability to obtain sufficient water in more arid environments. It is thought that Aplodontia prefer vegetation high in water content due to their poor ability to concentrate urine which makes it necessary to consume large amounts of water daily.

Diet

They exhibit coprophagy and eat soft fecal pellets to obtain maximum nutrients; hard fecal pellets are transferred to fecal chambers located within the burrow system. Food includes fleshy herbs and young shoots of more woody plants. Ferns probably make up the bulk of their diets. They appear to be strictly herbivorous. Their consumption of seedling trees has led some to consider them as pests.

Ecology

Known predators include bobcats, coyotes, cougars, golden eagles, and owls. Among the parasites of the mountain beaver is the largest flea known, Hystrichopsylla schefferi. Females of this flea can be 8 mm (0.31 in) long.

Mountain Beavers are considered pests in areas of the PNW because of the extensive damage they cause to forest trees due to basal-grinding (removal of bark), branch cutting, or clipping small sapling and seedlings. This damage often poses a problem for forest management and reforestation as smaller seedlings are buried or uprooted. Most often the damage comes from feeding damage resulting in, deformities, growth suppression, and mortality.

Damage control measures taken to protect forest trees by controlling the Mountain Beaver population via trapping, placing toxic baits, and placing physical barriers (eg. plastic mesh tubes) around the base of an individual tree.