Aplodontia rufa
mountain beaver

Mountain beavers are found in North America. The two main ranges of mountain beavers are from Merritt, British Columbia to Rio Dell, California and from Mt. Shasta, California to western Nevada. There are also sparse populations of this species on the Californian coast (Carraway, 1993).

The habitat of mountain beavers ranges from forested areas at sea level to timberline peaks. They enjoy areas that contain second growth tree species, shrubs, and prefer to be near water. They are most abundant in high mountain peaks with decidous forest and are least common in coniferous forests. Mountain beavers must live in places with deep soils in order to construct their burrow system. (Carraway, 1993).

Mountain beavers are dark brown except for a white spot below each ear. They have strong incisors. Their head is flat and wide and their nose is slightly arched. The body is thick, heavy, and covered with coarse, dull fur. Underneath the fur is a sparse covering of guard hair, which is dark red of grayish brown in color. They have short limbs and their total length is 300 - 470 mm (Carraway, 1993).

Beginning in November or December, there is an increase in the size of the testes, prostate and bulbourethal glands of males. As females reach estrous, their nipples increase in size, their vulva swell, and vaginal smears reveal predominately ephithelial cells. Females that are only a year old ovulate as well but no breeding occurs, demonstrating that ovulation is spontaneous instead of being triggered by copulation. The onset of the estrous cycle is around February or March.

Gestation usually lasts six to eight weeks and litters of two to three young are common. The weight of the young beavers is 25.5g. At birth, the beavers are pink, helpless, blind, and do not have a considerable covering fur. Within six to eight weeks the beavers are able to function (Carraway, 1993).

Mountain beavers are not very social animals. Rarely do they go farther than a few meters from their burrows. Their home ranges overlap and each beaver defends its nest site. The sight and the hearing of the mountain beaver are very poor but their senses of smell and touch are well developed. Mountain beavers vocalize in the form of whistles and booming sounds. They also squeal while fighting and make a grinding noise with their teeth (Carraway, 1993).

The burrow system of mountain beavers is centered around the nest sites. Almost all the entrances are connected to the underground nest chambers. The nest chambers are carpeted with dried leaves. The opening to the tunnels are covered with tent like stick structure or have vegetation covering the opening (Carraway, 1993).

Mountain beavers are herbivorous animals; their diet includes forbs, grasses, and even ferns such as sword fern and bracken fern. The composition of the diet of mountain beavers differs depending on the sex and age of the individual and the season. While they are eating, they squat and emit hard and soft fecal pellets which they catch in their mouths. The hard pellets are put into a pit next to the vegetation while the soft pellets are reingested (Carraway, 1993).

Foraging by the mountain beavers on seedlings in areas undergoing reforestation can lead to environmental and economic damage. They also cause garden damage and raid the crops of farmers. To prevent further damage by the mountain beavers, people take various types of action. One is to reduce the food consumed by mountain beavers by using herbicides and burning. Another method is to control the population directly by traps or through using toxic baits. Plastic mesh has also been put around trees that the mountain beavers destroy. These prevention measures add to a considerable amount of money (Carraway, 1993).

The IUCN lists the subspecies A.r. nigra and A.r. phaea of the mountain beaver as indeterminate (Wilson, 1993).