Pack Rat (Bushy-Tailed Wood Rat)

Pack Rat (Bushy-Tailed Wood Rat)

pest115The bushy-tailed wood rat, otherwise locally known as the pack rat is the only native rat found in Canada. It is immediately distinguished from the introduced Norway and roof rats by its bushy tail.

It is a large, gentle, squirrel-like rodent. Its adult fur coat is long, soft, dense, usually grey on the back and with tawny brown sides. The undersides and feet are white.

Measurements of males are: total length, 280 to 460mm (11 to 18”), tail, 105 to 222mm (4 to 8.75”), weight, 211 to 526g (7.4 to 18.4oz.). Males are eight to 10% larger than females.

Wood rats are active all year and primarily solitary and nocturnal. They are most active during the first half hour after sunset and dawn. One individual to 20 acres is an average density in its preferred habitat. Their presence is characterized by their large bulky residence composed of twigs, bones, foliage, debris and all manner of human artifacts, some containing up to three bushels of material. Their actual nest is sited in the centre of this mound, and is made of shredded bark, grass and moss—and if in human environments, soft, shredded cloth, cotton batting, wool, etc. The nest itself is tidy but nearby are the toilet areas, where the waste encrusts and stains and cements loose debris to the rocks.

For food, they prefer the leaves of aspen, willows, roses, cherries, currants, snowberries and elderberries, but will also eat the twigs and needles of Douglas-fir, Alpine Fir, Englemann Spruce and Junipers. They also use the seeds and fruit of Douglas-fir, anemones, gooseberries, cinquefoils, raspberries, fireweed, gentians, elderberries, honeysuckles and goldenrod. In autumn, they are provident, collecting and curing the available food items, and stockpiling them in crevices and under large boulders for their winter needs.

Beginning in February, the male meet up with a female and pursues her until they mate in March. The gestation period is 27 to 32 days. After the young are born, the female, who is dominant, drives out the male. The litter size is one to six (average three and a half). Under favourable conditions, two litters, about two months apart, are produced, but in the northern part of its range, usually only one. The young are weaned at age 26 to 30 days and reach maturity when about eleven months old.

Distribution within British Columbia

Most literature reports that the bushy-tailed wood rat is found throughout all of BC’s mainland and is absent from the coastal islands Some authors, however, report that this rodent is also absent from the northeast and northwest corners of the province. It is however very predominant in the Kootenay Region.

This rodent is not considered to be in jeopardy and is, therefore, not protected (Stevens and Lofts 1988).

Habitat Requirements

The bushy-tailed wood rat requires habitat that offers good security cover. Activity is significantly higher in areas that have 75 to 100% cover than in areas with less cover. The cover provided within rocky habitats such as talus slopes, caves, cliffs, river canyons, and rock outcrops in open forests appear to be favorite habitats for this wood rat. In the absence of rocky habitat, security cover can be provided by logging slash, hollow logs, abandoned buildings and mine shafts.

Wood rat habitats provide wood rats with suitable sites for building their stick “houses”. Wood rats owe their other common name of pack rat to their association with stick houses, which are generally quite large (one to 1.8m in height) and built out of woody debris, dried vegetation, and other objects the wood rat can collect, including human artifacts such as silverware, jewelry and clothing. These houses are preferably situated within the shelter of a rocky overhang, but can sometimes be found in the open, up a tree, or in the attic space of your home

Although they are often referred to as houses, the piles of debris created by wood rats do not often function as shelters and wood rats do not usually reside therein. Large wood rat piles function more as a storage dump than a house. Their true nests are small (about 15cm in diameter), cup-shaped, and are made up of finely shredded bark and other soft materials such as fur. These nests may be found within the larger stick house, but are more commonly found in a sheltered spot nearby.

Food Habits

The wood rat is an omnivorous rodent that will make a meal out of a variety of plants, insects, small amphibians, and carrion. The majority of the wood rat’s diet is comprised of green and dry vegetation. Preference is shown for the foliage of herbs, shrubs, and trees, but not grasses. They also feed on the vascular tissues of Douglas-fir, Sitka spruce, and western hemlock. Willow leaves are also a favoured food. Bushy-tailed wood rats stockpile large quantities of dried vegetation to sustain them throughout the winter months.

pest116Daily Activity and Movement Patterns

The bushy-tailed wood rat is nocturnal in activity, but can be observed occasionally during the day. They will rarely venture far from the nest. Although the bushy-tailed wood rat can climb trees, and will occasionally locate its stick house up a tree, it is less arboreal than its semi-arboreal cousin, the dusky-footed wood rat.

Bushy-tailed wood rats are a solitary species that defend territories. Males spend considerable time marking their territory with their ventral musk glands, which they rub on toilet posts, food caches, and nests. This can also create a very recognizable odour when found nesting inside your home.

Seasonal Activities and Movement Patterns

The bushy-tailed wood rat does not hibernate; instead it actively prepares for the winter by stockpiling a cache of vegetation, which it gathers and dries in the sun during the growing season. Winter months are primarily spent below the snow among the cover provided by their rocky habitat, however, short trips may be made over the snow’s surface.

Wood rats remain solitary, except during the breeding season, which in BC begins in late March and lasts until late May. After a gestation period of 27 to 32 days females give birth to an average of four young (range of one to six) during early May to late June. Several authors report that the bushy-tailed wood rat has multiple litters per year. However within BC, the wood rat is commonly reported as having only a single litter per year.

Bushy-tailed wood rats do not travel significant distances throughout the year (with perhaps the exception of dispersing juveniles), remaining in the near vicinity of their stick houses and nesting sites.

Physical Signs

Good indicators of bushy-tailed wood rat presence are the deposits of urine and feces that accumulate within this animal’s home range. Feces and urine can form a thick tar-like substance (often mistaken for some kind of mineral), if deposited in a spot sheltered from the rain, such as within a cave or under a rock overhang. Bright white streaks result from urine deposited on rocks not sheltered from the rain. The rain is thought to leach out the organic components of the urine leaving a white calcareous deposit behind. These white deposits are useful sign to look for when sampling for bushy-tailed wood rats, as they can be observed from a distance and are often indicative of occupation (or former occupation) of an area by a wood rat.

Because feces and urine deposits are very persistent, lasting for thousands of years in sheltered areas such as caves, and decades on exposed surfaces such as cliffs, care must be taken not to confuse past use of a site with that of current use. Simply locating fresh streaks of urine can quickly answer this question. Fresh urine can be recognized by its transparent yellow to opaque brown colour, skunky odour and stickiness.

Stick Houses

Bushy-tailed wood rats are or have recently been present in a study area if an investigator discovers the large stick “houses” used by this wood rat. These structures, made primarily out of woody material and a variety of other debris, are often located in a sheltered area such as a cave, under a rock ledge, within an abandoned building, around the base of a tree or log, inside a hollow snag, or sometimes even up a tree. Although wood rat “houses” are usually not placed in the open, because of their large size (0.9 to 1.8m), they can usually be spotted with relative ease.

Damage Caused by Feeding and Construction

Because the bushy-tailed wood rat is an animal that feeds on a large variety of plants within its home range, clipped shoots and branches, with the usual oblique cut common to most rodent feeding scars, are possible indicators of wood rat presence. However, such feeding sign is difficult to distinguish from other rodent feeding damage. A less ambiguous sign produced by this wood rat are the patches of bark removed from the boles of trees for nest construction. From a distance, this debarking may be confused with that of the porcupine or tree squirrels. Unlike the tree squirrels that discard the bark and feed on the exposed sapwood, the bushy-tailed wood rat transports all of the removed bark to its nest for construction. Therefore, there will be no discarded strips of bark found beneath the trees damaged by bushy-tailed wood rats, as there would beneath trees damaged by tree squirrels or porcupines. In addition, wood rats do not feed on the sapwood, rather they just remove the outer bark (often the sapwood is not even exposed), whereas, porcupine and tree squirrel feeding will always expose the sapwood.