San Joaquin Valley Riparian Woodrat

Neotoma fuscipes ssp. riparia

Description

The San Joaquin Valley riparian woodrat is a medium-sized rodent, approximately 17.4 in (443 mm) long, including its 8.5 in (217 mm) furred tail, and 7.05-14.11 oz (200-400 g) in weight depending on the season.

This woodrat can be distinguished from other subspecies of Neotoma fuscipes by its larger stature, lighter weight, more grayish coloring, white hind feet, and a more distinctly bicolored tail. Skull measurements and characteristics are also distinctive.

Behavior

Riparian woodrats are mostly active at night. They feed on leaves, fruits, terminal shots of twigs, flowers, nuts, and fungi.

Studies on related subspecies show that the woodrats live in loosely cooperative societies with a matrilineal social structure. Males are territorial and aggressive, and mate with more than one female in a breeding season. Females stay near their birth site throughout their lives.

Young are born in all months of the year in stick nest houses, or lodges, on the ground approximately 2-3 ft (0.6-0.9 m) high and 4-6 ft (1.2-1.8 m) in diameter, which can last 20-30 years if not destroyed by flooding. Occasionally the woodrat will build nests in tree cavities or artificial wood duck nest boxes.

Some studies show that populations fluctuate widely in response to habitat alteration such as fire, flood, drought, browsing, and trampling.

Habitat

Primary habitat for the riparian woodrats are deciduous valley oaks where there are few live oaks. Most occur in dense shrub cover intermixed with few open areas. The highest densities are found in willow thickets with an oak overstory.

Studies of the N. fuscipes also show that these woodrats often cross ecotone boundaries as long as there is adequate habitat.

Distribution

Historically, the riparian woodrat could be found as far away as 6 mi (10 km) from the one remaining current population. In 1938, specimens had been collected 2 mi (3 km) northeast of Vernalis, west of Modesto in Stanislaus County, California. In the 1970s, a population was reported near Vernalis, but current status is unknown.

The single riparian woodrat population is found on 253 acres (102 hectares) of riparian forest on the Stanislaus River in Caswell Memorial State Park, in San Joaquin County. Estimates have shown the population to be as large as 637 individuals in 1992, but numbers have since dropped. From April 1997 to March 1998 15 riparian woodrats were live-trapped at the State Park.

Threats

There has been a nearly 90% reduction of historical riparian communities throughout the riparian forests along major streams flowing onto the floor of the northern San Joaquin Valley due to urban, commercial, and agricultural development, wood cutting, reclamation and flood control activities, groundwater pumping, river channelization, dam construction, and water diversions.

Due to habitat limitations, as well as small population size, the riparian woodrat is at risk of being further harmed by naturally occurring events.

The increase of habitat conversion to agriculture combined with construction of dams has altered the timing, frequency, duration, and intensity of flooding. Although woodrats can easily climb trees, and avoid drowning, their nests, which are essential to survival, can be destroyed.

Wildfires are of great concern as well because of habitat degradation and loss of individuals who cannot escape the fire.

In addition, disease, predation, potential competition with the exotic black rat, rodenticide, and loss of genetic variability from inbreeding all affect the viability of the riparian woodrat.

Conservation and Recovery

No specific conservation measures have been put in place to protect the riparian woodrat, but the habitat of the woodrat does receive protection via a management plan to protect riparian brush rabbits. Some studies of woodrats and small mammals have been supported by the California Department of Parks and Recreation.

San Joaquin County is developing a multispecies habitat conservation plan which considers habitat for the riparian woodrat. Some of the measures suggested under the plan may benefit or minimize negative impacts to the woodrat.

A fire management plan has also been initiated for the Park to protect habitat, but fires from outside sources still pose a threat.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
(503) 231-6121
http://pacific.fws.gov/

Sacramento Fish and Wildlife Office
U. S. Fish and Wildlife Service
2800 Cottage Way, Room W-2605
Sacramento, California 95825-1846
Telephone: (916) 414-6600
Fax: (916) 460-4619

References

Sakai, H.F and B.R. Noon. "Dusky-Footed Woodrat Abundance in Different-Aged Forests in Northwestern California." Journal of Wildlife Management 57 (2): 373-82.

United States Department of the Interior. 23 February 2000. "Endangered and Threatened Wildlife and Plants: Final Rule to List the Riparian Brush Rabbit and the Riparian, or San Joaquin Valley, Woodrat as Endangered." Federal Register 65 (36):8881-8890.