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Douglas Squirrel

Tamiasciurus douglasii

Associations 3

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

Associations 4

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)

Behaviour 5

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 ; tactile ; acoustic ; chemical

Conservation status 6

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

Cyclicity 7

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

Description 8

"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."

Links:
Mammal Species of the World
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Distribution 9

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 )

Distribution 10

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.

Ecology 11

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

Ecology 11

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

Economic uses 12

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

Habitat 13

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

Habitat and ecology 14

Habitat and Ecology

It inhabits coniferous forests, in upper pine belt and in fir, spruce, hemlock forests. It 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 trees in summer; roosts in tree holes in winter.

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

Predators include bobcats, martens, coyotes, and large owls. In spring it feeds on new shoots of conifers, inner bark and developing needles; in summer, some green vegetation, fruits and berries. In autumn it eats seeds from conifer cones. May also eat tree sap, fungi, and nuts. Stores cones in a log or burrow. Active throughout the year but usually remains in nest during severe weather. Daily activity begins at dawn and ends at sunset.

Systems
  • Terrestrial

Life expectancy 15

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

Management 16

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).

Migration 17

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.

Morphology 18

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

Other Physical Features: endothermic ; bilateral symmetry

National distribution 19

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

Population 20

Population

This species is considered to be common. Populations fluctuate with variations in food supply. Densities range from 0.2 - 0.5 per hectare.

Population Trend
Stable

Range description 21

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.

Reproduction 22

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); sexual ; 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)

Size in north america 23

Sexual Dimorphism: None

Length:
Range: 270-348 mm

Weight:
Range: 141-312 g

Taxonomy 24

Comments: Tamiasciurus douglasii formerly included T. mearnsi, which was regarded as a distinct species by Lindsay (1981) and Hoffmann et al. (in Wilson and Reeder 1993) and Thorington and Hoffman (in Wilson and Reeder 2005). MtDNA and allozyme data cast doubt on the validity of T. mearnsi as a distinct species; at most, it probably should be regarded as a subspecies of T. douglasii, which itself is doubtfully distinct from T. hudsonicus (Arbogast et al. 2001).

Based on patterns of genetic variation and morphology, Arbogast et al. (2001) suggested that Tamiasciurus should be regarded as comprising one species with three subspecies (hudsonicus, douglasii [including mearnsi], and mogollonensis); mogollonensis represents a southwestern clade that occurs in Arizona, New Mexico, and adjacent parts of southern Colorado and southeastern Utah. Alternatively, Arbogast et al. (2001) suggested that these three taxa might be recognized as separate phylogenetic species. Pending further support for this rearrangement, the North American mammal checklist by Baker et al. (2003) did not accept Arbogast et al.'s (2001) proposed reorganization of Tamiasciurus as a single species. Thorington and Hoffmann (in Wilson and Reeder 2005) also recognized douglasii, hudsonicus, and mearnsi as distinct species.

Earlier, Hall (1981) had suggested that T. douglasii and T. hudsonicus might be conspecific, but Lindsay (1982) concluded that apparent hybrids probably were examples of character convergence.

Threats 25

Major Threats

There are no major threats to this species throughout its range. It may be locally threatened by deforestation and habitat fragmentation.

Trophic strategy 26

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 )

Uses 27

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

Uses 28

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

Sources and Credits

  1. (c) Kim Cabrera, some rights reserved (CC BY-NC-ND), uploaded by Kim Cabrera
  2. (c) C.V. Vick, some rights reserved (CC BY-NC-ND), http://www.flickr.com/photos/45153605@N00/1353192473
  3. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31426151
  4. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31426150
  5. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31426148
  6. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31426154
  7. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28916140
  8. (c) Smithsonian Institution, some rights reserved (CC BY), http://eol.org/data_objects/16147009
  9. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31426143
  10. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28916130
  11. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28916136
  12. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28916133
  13. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31426144
  14. (c) International Union for Conservation of Nature and Natural Resources, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31281130
  15. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31426147
  16. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28916134
  17. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28916137
  18. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31426145
  19. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28916131
  20. (c) International Union for Conservation of Nature and Natural Resources, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31281129
  21. (c) International Union for Conservation of Nature and Natural Resources, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31281128
  22. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31426146
  23. (c) Smithsonian Institution, some rights reserved (CC BY), http://eol.org/data_objects/6625806
  24. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28916125
  25. (c) International Union for Conservation of Nature and Natural Resources, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31281131
  26. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31426149
  27. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31426152
  28. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31426153

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