Point Arena Mountain Beaver

Introducing Point Arena Mountain Beaver (PAMB)

Aplodontia rufa nigra

Presented by BioConsultant

122 Calistoga Road #360 Santa Rosa, CA 95409 707-539-4488

kfitts@bioconsultant.net www.bioconsultant.net

Taxonomy

PAMB is one of seven recognized subspecies of Aplodontia.

Aplodontia Range

The seven subspecies range from southern British Columbia to Point Reyes, California and the Cascade and Sierra Nevada Ranges.

Reasons for Subspecies Status

Genetic isolation

Unique black coloring

Certain anatomical features

PAMB Distribution

PAMB is known only from 62 square kilometers (15,320 acres) in coastal Mendocino County.

The USFWS considers the potential range to be located south of a point two miles north of Bridgeport landing, north of a point five miles south of the town of Point Arena, and to a distance of five miles inland from the Pacific Ocean.

In 1988, 26 separate known populations had been documented, with an estimated 200-500 animals total. To date more PAMB locations have been discovered.

Description

Mountain beaver are semi-fossorial rodents and well adapted for their burrowing lifestyle. They are stout, compact, and shaped like a football. The front legs are muscular and well adapted for digging with long curved claws.

An average adult Aplodontia weights between 2-4 lbs and measures approximately 12 inches.

PAMB are the smallest of the California subspecies and are distinguished by their unique black coloring.

Life History

Reproduction:

Aplodontia have an unusually low reproductive rate for rodents; females usually do not bear young until their second year, have a single litter, with an average of 2-3 young (Scheffer 1929).

Pfeiffer (1958) performed reproductive studies on several subspecies of mountain beaver and found that there is a sharply defined and extremely limited breeding season of approximately 5-7 weeks.

All the females of a given population ovulate spontaneously together at about the same time each year.

Breeding Season:

The USFWS PAMB restriction period:

Breeding Season- Dec. 15 through June 30

Dispersal Season - April 15 through Sept. 30

Some evidence suggest that the subspecies along the temperate northern California coast may have an earlier breeding season than those in the Pacific Northwest.

Aplodontia in the Pacific Northwest breed in February / March with parturition in late March and early April.

Pfeiffer estimated a PAMB parturition date of February 20, this indicates a breeding season from December to early January.

BioConsultant sighted a PAMB Juvenile: On April 30, 2002 est. birth date: March 2 est. breeding date: January 31

Life Span

5-6 years

Predators of Aplodontia

Bobcat

Great horned owl

Mountain lion

Coyote

Golden eagle

Mink

Fisher

Domestic dogs

Short-tailed weasel

Red-tailed hawk

Human activity is by far the mountain beaver's greatest threat.

Water and Dietary Requirements

Aplodontia have primitive simple kidney structure

Unable to concentrate urine effectively

Require large quantities of water daily- a diet heavy with succulent plants (Nungesser and Pfeiffer 1965).

Ecology

Distribution Pattern:

Aplodontia exhibit a contagious/clumpy distribution pattern

A population consists of groups of individuals, each with their own burrow system.

Aplodontia will readily move into vacated systems

Burrow System:

A typical burrow system includes chambers for nests, latrines, food storage and feeding, and perhaps earth ball storage areas. The complexity and numbers of chambers and burrows depends upon the age of the system. Old systems are recognized by well worn, hard packed burrow floors and smooth burrow walls. A sub-adult system may contain only two or three chambers, for a nest, fecal deposition, and food storage/feeding.

Home Range Size:

Aplodontia are considered solitary animals and defend their individuals nest sites and adjacent burrows, but tolerate sharing the outer burrows where home ranges overlap.

They will avoid contact except for the short breeding period, even though their home ranges overlap significantly.

Martin (1971) reported the average home range size varied from 0.08 to 0.5ac with an average of 0.3ac.

Lovejoy (1979) reported the average home range size of 0.79ac for males and 0.42ac for females.

New research at the Olympia Field Station in Washington reported a substantially larger average home range size of 10.27ac and 2.89ac on a second site of different habitat.

Plant Community Types Associated With PAMB

PAMB are found in many plant community types and areas of transition.

1. Northern coastal scrub

2. Coastal bluff scrub

3. Northern riparian scrub

4. North coast riparian

5. Coastal prairie

6. Northern dune scrub

7. Fresh water seep

8. Alder/herbaceous ground cover

9. Conifers/sword fern

10. Roadside habitat

Areas not considered as potential habitat are those containing only annual grasses, or those comprised of conifers or hardwoods with little or no ground cover.