Point Arena Mountain Beaver: Leave it to This Beaver to Become Endangered

The Point Arena Mountain Beaver: Leave it to This Beaver to be Endangered

By: Katelyn Matroni

(Google Images, 2015)

Official Status: Federally listed under the Endangered Species Act as endangered and is considered a

mammalian species of special of concern by the State of California.

Date Listed: December 12, 1991

Recovery Plan: Published in 1998

Aplodontia rufa nigra (Google Images, 2012)

Description and Ecology

The Point Arena Mountain Beaver (Aplodontia rufa nigra) are considered the most primitive living

rodents. These beavers are one of seven subspecies of mountain beavers. They are stout, compact,

and cylindrical and have a broad and laterally compressed skull. They average about one foot in

length and two to four pounds in weight. Compared to other beavers, they have a unique blackish

coloration. There is a 1:1 ration of males to females and these beavers are thought to have a very low

reproductive output. The females breed in their second year and then produce a single litter each year

of two to three offspring. They have a small breeding season from December 15 to June 30 with

dispersal occurring from April 15 through September 30. The beavers are semi-fossorial and spend

most of their time in underground burrow systems. When they do surface above ground it is to forage

on vegetation. Studies show that the most important factors for their habitat use are cool thermal

regime, adequate soil drainage and softness, an abundant food supply, and a high cover of woody

plants. Mountain beavers are herbivorous and never eat meat. They are able to eat many plants that

are toxic to other animals like stinging nettle. (USFWS, 2011)

Beaver Burrow (USGS, 2015)

Map Of Area (Google Images, 2000)

Geographic Range and Population

The Mountain Beavers were discovered by Lewis and Clark and have been known to occur in many

areas around the Pacific Northwest. The Point Arena subspecies is only found in a 24 square mile

area in western Mendocino County, CA. Their range include five miles inland from the Pacific Ocean

extending from a point 2 miles north of Bridgeport Landing south to a  point 5 miles south of the

town Point Arena. The total population size for the mountain beavers is unknown. It is unclear how

many separate sub-populations exist but there are probably around 26 different ones. The amount of

occupied and unoccupied but suitable range is unknown. Within Manchester State Park, there are 481

acres of suitable habitat, 57 of those are considered occupied. (USFWS, 2011)

Threats

The primary reason the Point Arena Mountain Beaver became listed was there extreme decline in
numbers quickly. Their main threats are habitat loss and fragmentation, primarily due to construction
of recreational facilities, urban development, conversion to agricultural use, and construction of
transportation and utility corridors. Livestock can also alter vegetation and crush these beavers’
burrows. Additional threats are rodent control, domestic pets, invasive plants, and vegetation fires.
Timber harvest can disturb or kill the beavers as well. They are highly susceptible to disturbance
from loud noises and ground vibration during breeding seasons as they have highly developed tactile
senses.(USFWS, 2011)

Human Holding Beaver (Google Images, 2015)

Recovery Plan

The ultimate goal of this plan is to delist the Point Arena mountain beaver and criteria for down
listing to “threatened” are also established. The overall actions needed and implemented by the plan
are to:

1.       Protect known populations

2.       Protect suitable habitat, buffers, and corridors

3.       Develop management plans and guidelines

4.       Gather biological and ecological data necessary for conservation of the subspecies

5.       Determine feasibility of, and need for, relocation

6.       Monitor existing populations and survey for new ones

7.       Establish an outreach program

Each action has a series of steps and tasks associated with it to delist this species. The overall
estimated cost of recovery is $1,047,000 or higher, the costs for several tasks needed for recovery
have not been determined. (USFWS, 1998)

References

"Point Arena Mountain Beaver Species Profile." U.S Fish and Wildlife. Arcata Fish and Wildlife

Service, 11 Apr. 2011. Web. 04 June 2015.

<http://www.fws.gov/arcata/es/mammals/mtnBeaver/mtnbeaver.html>.

U.S. Fish and Wildlife Service. 1998. Point Arena Mountain Beaver (Aplodontia ru/a nigra

(Rafinesque)) Recovery Plan. Region 1, Portland, OR. 71 pp.