Tamiasciurus douglas (Bachman, 1839)
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publication ID |
https://doi.org/ 10.5281/zenodo.6840226 |
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DOI |
https://doi.org/10.5281/zenodo.6818748 |
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persistent identifier |
https://treatment.plazi.org/id/064D0660-FFD2-ED10-FAF1-F6E7FC63FD82 |
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treatment provided by |
Diego |
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scientific name |
Tamiasciurus douglas |
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Douglas’s Squirrel
French: Ecureuil de Douglas / German: Douglas-Rothérnchen / Spanish: Ardilla de Douglas
Other common names: Chickaree; Mearn’s Squirrel (mearnsi)
Taxonomy. Sciurus douglasii Bachman, 1839 ,
“Shores of Columbia River.”
Restrict- ed by]. A. Allen in 1898 to mouth of Columbia River, Clatsop County, Oregon, USA.
Three subspecies are recognized.
Subspecies and Distribution.
T.d.douglasi:Bachman,1839—PacificcoastofWashingtonandOregon(WUSA).
T.d.mearnsiTownsend,1897—SierradeSanPedroMartir,BajaCalifornia(NWMexico).
T. d. mollipilosus Audubon & Bachman, 1841 — inland in British Columbia (SW Canada) and Washington, Oregon, and California (W USA).
Descriptive notes. Head—body mean 181 mm (males) and 185 mm (females), tail mean 119 mm (males) and 145 mm (females); weight mean 206-9 g (males) and 199-3 g (females). Douglas’s Squirrels have an olivaceous gray to gray-brown dorsum, often with rust or chestnut medial band that extends length of body. In summer, lateral black stripe separates dorsal and ventral color from under parts, but it less apparent in winter. Snout and chin are often more pale or buff; distinct eye rings are white to buff. Ear tufts of black tipped hairs can be visible, particularly in winter. Venter is white to pale buff to yellowish or red-orange. Tail is similar in color to dorsum butis frosted
with buffor white-tipped hairs; ventral side displays faint black longitudinal banding near tips of hairs. Subspecies mollipilosus has whitish, not yellowish, frosting on tail. Chromosome numberis 2n = 46.
Habitat. Pure and mixed stands of conifers, especially pine (Pinus), fir (Pseudotsuga, Abies), spruce (Picea), and hemlock (7suga), all Pinaceae, and forests with deciduous component, especially in riparian corridors. Douglas’s Squirrels are considered old growth dependent, but densities do not vary considerably with forest age. Thinning to below 50% of existing forest cover can have negative impact. Douglas’s Squirrel persists in areas of suburban housing and urban parks with sufficient mature tree cover.
Food and Feeding. Douglas’s Squirrel is primarily herbivorous and feeds heavily on tree seeds, buds, cambium, and fruits but also eats significant amounts of mushrooms and other epigeous and hypogeous fungi when available throughout the year. Individuals will opportunistically eat insects, avian nestlings, and eggs and scavenge carcasses and bones. Tree seeds are often cached by scatterhoarding in many locations and larderhoards known as middens. Seeds are readily eaten from mid-summer ripening until caches are depleted in winter. With depletion of seed stores, Douglas’s Squirrels feed extensively on buds and cambium of conifer branch tips. Fungi, especially hypogeous truffles, are used heavily in summer and are often cached in tree branches and cavities.
Breeding. Douglas’s Squirrel nests in leaf and twig nests constructed in the canopy, cavities in live or dead trees, and rarely burrows or logs on the ground; young are born within these nests. Breeding season begins in March and peaks in spring but can continue for several months into early summer with second peak common when food is abundant and climate is mild. Female Douglas’s Squirrels are in estrus for a single day during the breeding season when several males converge on a female's territory and chase her during the entire day. A female mates with one or more males. Douglas’s Squirrel ovulates spontaneously, resulting in immediate conception. Litters have 4-8 young. Gestation is ¢.33 days. Individuals reach sexual maturity at 10-12 months and rarely reproduce in the first year. Juveniles appear to disperse from natal areas.
Activity patterns. Douglas’s Squirrels are diurnal. They do not hibernate and are active throughout the year. Activity is unimodal around midday in winter and shifts to bimodal from spring to autumn. Inactive squirrels sleep in leaf and twig dreys in the canopy, tree cavities or logs, and occasionally burrows.
Movements, Home range and Social organization. Douglas’s Squirrels are asocial and typically defend exclusive territories, established around a single larderhoard of food resources at the center of the territory. Territory size is inversely related to cone crops but is generally less than 1 ha. The “Mearn’s Squirrel” (7. d. mearnsi) is not territorial and does not focusits activities around a larderhoard. Home ranges of Douglas’s Squirrels are larger for males (mean 17-1 ha) than females (mean 5 ha), especially during the breeding season; home range overlap is extensive. Individuals travel averages of 307-614 m from their nocturnal nest, with juvenile and adult males moving greater distances than females. Most interactions between individuals are agonistic because individuals aggressively defend territorial boundaries with vocalizations and chases. Densities are 0-03-0-9 ind/ha in different forest types. Minimal sex differences in space use have been reported. Alarm calls can be high-pitched whines that follow a series of chatters or chucks. A loud territorial call known as the rattle reverberates through the forest, especially in autumn when food resources are stockpiled.
Status and Conservation. Classified as Least Concern on The IUCN Red List. Population trend of Douglas’s Squirrel is stable. Lack of information on ecology, naturalhistory, or threats likely impedes conservation and management efforts; it might be vulnerable to thinning and deforestation. The “Mearns’s Squirrel”is classified as Endangered on The IUCN Red List (as 1. mearnsi). It is threatened in Mexico. Population trend is decreasing. Distribution of Mearns’s Squirrelis severely restricted (c.40,000 ha) across three sites. Eastern Gray Squirrels (Sciurus carolinensis) were released into this area more than 70 years ago but do not appear to have spread through the habitat of Mearns’s Squirrels. Entire distribution of Mearns’s Squirrel is within a protected area, but illegal logging occursin this area.
Bibliography. Allen (1989b), Buchanan etal. (1990), Carey (1995), Chavez et al. (2014), Flyger & Gates (1982), Hope et al. (2016), Ingles (1965), Keane etal. (2006), Koford (1982), Koprowski, Ramos etal. (2006), Lair (1985), Larsen & Boutin (1994), Lomolino & Perault (2001), McKeever (1964), Perault & Lomolino (2000), Ramos-Lara & Koprowski (2012, 2015), Ramos-Lara et al. (2013), Ransome (2001), Sanders (1983), Smith, C. C. (1965, 1968, 1978, 1981), Smith, W. P, et al. (2003), Steele (1998, 1999), Steele & Koprowski (2001), Steele et al. (2005), Sullivan & Sullivan (1982), Thorington et al. (2012), Yahner (2003), Yensen & Valdés-Alarcon (1999).
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