Tamiasciurus douglasii

"Douglas's Squirrels are small, energetic, and very active during the day all year long. They spend many hours collecting and storing green pine cones to eat during the harsh winters. Each squirrel builds several nests, including an underground nest for winter use. They usually breed from March to June, and sometimes again in late summer or early fall, and other than that, are solitary. Females have eight teats, and litters of eight have been recorded, but litters of 4-6 are more usual."

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This species occurs on the Pacific Coast and Sierra Nevada and Cascade ranges of North American, from southwestern British Columbia in Canada, through the Cascade Range of western and central Washington and Oregon, southward along the coast of northern California to San Francisco, and southward through the Sierra Nevadas to south-central California in the United States.

Douglas squirrels are found along the Pacific coast of North America. Their range is limited to northern California, west and central Oregon, western Washington and southwestern British Columbia, Canada.

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Southwestern British Columbia south through coast ranges, Cascades, and Sierra Nevada to southern California. Related species (T. MEARNSI) occurs in Sierra San Pedro Martir, northern Baja California, Mexico.

There are no characteristic differences between the physical appearances of female and male Douglas squirrels. The adult body length ranges from 270 to 355 mm. The tail ranges from 100 to 160 mm. The hind feet range from 44-60 mm. Weight range is 141-312 g.

Douglas squirrels have distinct summer and winter coats. Their summer pelage ranges from reddish-brown to grayish-brown on the backside. Many of these hairs are orange or black at the ends. The underside ranges from light to dark orange, sometimes with white areas. It is this orange coloring on the chest and belly that sets Tamiasciurus douglasii apart from its nearest relative, the red squirrel. Douglas squirrels have a broad, bushy tail, the dorsal side of which is similarly colored to the back, with a black tip. The tail's underside is reddish-brown in the center, fading out to black, and then to light orange or white at the edges. Douglas squirrels have a black stripe that runs along their sides. This stripe is lacking in juveniles and faded or absent in winter. The winter pelage is more gray overall; thus, the orange of the underside becomes less visible. In the most northern part of its range, Tamiasciurus douglasii may also have ear tufts in winter.

Range mass: 141 to 312 g.

Range length: 270 to 355 mm.

Sexual Dimorphism: sexes alike

Length: 36 cm

Weight: 300 grams

Sexual Dimorphism: None

Length:
Range: 270-348 mm

Weight:
Range: 141-312 g

Habitat and Ecology

Systems

• Terrestrial

Douglas squirrels mainly inhabit conifer forests; on occasion, they are found in other forests where conifer trees are present. Their elevation ranges from sea level to 3300 meters.

Douglas squirrels make their homes in nests. In summer, they usually build their nest of twigs, mosses, lichens and shredded bark. Sometimes they will occupy empty bird nests. The nests can be found in the forks of trees or further out on the limbs. In winter, they often build their nest in tree crevices, in holes from deserted woodpecker nests, or underground, under their food cache.

Range elevation: 0 to 3300 m.

Habitat Regions: temperate

Terrestrial Biomes: forest

Comments: Coniferous forests, in upper pine belt and in fir, spruce, hemlock forests. Occurs from the Transition to the Hudsonian life zone. In Washington, populations generally were higher in old-growth than in younger forest (Buchanan et al. 1990). Makes nest of vegetation in tree in summer; roosts in tree holes in winter.

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Douglas squirrels feed on a wide array of foods. They are mainly granivorous; pine seeds make up large portion of their diet. Depending on the season, they also eat fungi, cambium of conifers, twigs, sap, leaves, buds, acorns and other nuts, mushrooms, fruits, and berries. From time to time, they also eat arthropods, birds eggs, and nestlings. In fall, Douglas squirrels cut green cones from the tops of trees and cache them in a damp place, so the seeds remain fresh to eat throughout the winter. They will also cut mushrooms and store them in the forks of trees to dry and eat during winter. Douglas squirrels often store more food than they will eat during the winter, which can be useful if food sources are poor in the spring. They are protective of their caches and will burrow through the snow to get to them.

Animal Foods: birds; eggs; terrestrial non-insect arthropods

Plant Foods: leaves; wood, bark, or stems; seeds, grains, and nuts; fruit; sap or other plant fluids

Other Foods: fungus

Foraging Behavior: stores or caches food

Primary Diet: herbivore (Granivore )

Comments: In spring feeds on new shoots of conifers, inner bark and developing needles; in summer, some green vegetation, fruits and berries. In fall eats seeds from conifer cones. May also eat tree sap, fungi, and nuts. Stores cones in log, burrow, etc

In eating the fruiting bodies of fungi, Douglas squirrels may help to distribute the fungi's spores through their feces. These spores may then develop mycorrhizal relationships with conifer roots. They probably also help disperse conifer seeds in carrying cones to their caches. They also use plants from their environment to build their nests.

Ecosystem Impact: disperses seeds; creates habitat

Species Used as Host:

• none known

Mutualist Species:

• none known

Commensal/Parasitic Species:

• none known

Predators of Tamiasciurus douglasii include bobcats, martens, coyotes, larger owls, long-tailed weasels, domestic cats, foxes, and goshawks. Douglas squirrels are alert and fast, helping to evade predators. Typically, they will not eat on the ground, since this inhibits awareness of their surroundings.

Known Predators:

• long-tailed weasels (Mustela frenata)
• American martens (Martes americana)
• coyotes (Canis latrans)
• bobcats (Lynx rufus)
• domestic cats (Felis silvestris)
• northern goshawks (Accipiter gentilis)
• foxes (Canidae)
• owls (Strigiformes)

Populations fluctuate with variations in food supply. Predators include bobcats, martens, coyotes, and large owls.

Douglas squirrels are very vocal and have a wide variety of calls. Maser describes them as “ranging from a low ‘chir’ or ‘burr’ to an explosive ‘bauf, bauf bauf.’” (Maser et.al., 1981) The squirrels communicate with each other when disputing over territory, during courtship, and when warning of danger. They presumably also use chemical signals (i.e. scent), like other squirrels, to communicate with each other.

Douglas squirrels have whiskers above and below their eyes, as well as on their noses, and chins. These allow tactile perception of their environment. Additionally, Douglas squirrels have very good vision and hearing, and a good sense of smell.

Communication Channels: acoustic ; chemical

Perception Channels: visual ; acoustic

Comments: Active throughout the year but usually remains in nest during severe weather. Daily activity begins at dawn and ends at sunset.

No information could be found on the lifespan of Tamiasciurus douglasii.

Like other squirrels, the courtship of Tamiasciurus douglasii consists of a mating chase in which the males and females call to and chase each other. This ultimately leads to coupling off and mating. Each Douglas squirrel has one mate per mating season.

Mating System: monogamous

Male Douglas squirrel testes become mature in spring. Reproduction occurs from January until mid-August with the greatest portion between March and May. Most females have only one litter per year, although occasionally a second litter is born in August or September. The gestation period ranges from 36 to 40 days. Females have eight mammae, and the litter size ranges from 1 to 8, with 4 to 6 on average.

Breeding interval: The majority of Douglas squirrels breed once a year.

Breeding season: Reproduction can occur from January through August, although it usually occurs from March to June.

Range number of offspring: 1 to 8.

Average number of offspring: 4-6.

Range gestation period: 36 to 40 days.

Range weaning age: 6 to 9 weeks.

Range time to independence: 4 to 7 months.

Range age at sexual or reproductive maturity (female): 8 to 9 months.

Range age at sexual or reproductive maturity (male): 8 to 9 months.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

Douglas squirrels are born blind and without hair, weighing between 13 and 18 g. Fur covers the body by 18 days, and the eyes open at around 26 to 36 days. The young stay in their mother’s nest until they are one-half to two-thirds the size of an adult, usually around mid-July to early August. Siblings and the mother remain in close contact when they first leave the nest. Weaning starts at 6 weeks and is finished by 9 weeks. After this, the young become more independent, but families remain together until December. A juvenile Douglas squirrel will reach adult body size after around 8 to 9 months. Most will reproduce the following summer.

Parental Investment: altricial ; pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)

Most males reproductively active March-May. Females produce 1, perhaps 2, litters/year. Litter of 2-8, usually 4-6, young is born in May-June. Young first venture to ground in August. Families stay together much of first year.

Year Assessed

Assessor/s

Reviewer/s

Justification

History

• 1996
  Lower Risk/least concern
  (Baillie and Groombridge 1996)

There are no known major threats to Douglas squirrel populations.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N4 - Apparently Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Population

Population Trend

Major Threats

Conservation Actions

Management Requirements: Silvicultural strategies designed to provide increased levels of cone production over time may be effective means of improving habitat quality of young forests (Buchanan et al. 1990).

Douglas squirrels can cause damage to homes. They also sometimes gather nuts from filbert orchards before they are ready.

Negative Impacts: crop pest; household pest

People often steal Douglas squirrels's green cone caches and sell the cones, which contain fresh seeds, to tree nurseries.

Comments: Sciurid mycophagy may play important role in forest ecology (Maser and Maser 1988).