Neotoma cinereabushy-tailed woodrat

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Geographic Range

Bushy-tailed woodrats are found in western North America, ranging from arctic Canada to northern New Mexico and Arizona. This species was thought to be restricted to higher elevations until very recently, when the first reports documenting Neotoma cinerea at elevations as low as 1200 m appeared. These findings lend support to molecular evidence which had earlier indicated that bushy-tailed woodrat populations were not isolated on mountain ranges throughout the Holocene. It is currently unclear whether these lowland populations are isolated by even lower valleys, or whether this species can exist in low, xeric areas as well. Bushy-tailed woodrats are currently found at elevations up to at least 3700 m. During the Pleistocene, N. cinerea is well-known at lower elevations, and its range extended south to southern Mexico. Up to thirteen subspecies are recognized. These subspecies are primarily defined based on geography and local ecology, and are not universally accepted.

(Escherich, 1981; Grayson and Livingston, 1989; Grayson et al., 1996; Mewaldt, 1982; Smith et al., 1995)

Habitat

Bushy-tailed woodrats occupy a range of habitats from boreal woodlands to deserts. They are cliff-dwellers, and are often found on isolated, high-elevation bouldery exposures under a variety of temperature and moisture regimes. They require adequate shelter inside the rocks, though they are occasionally found inhabiting abandoned buildings as well.

(Frase and Sera, 1993; Grayson and Livingston, 1989; Topping and Millar, 1996; Vaughan, 1990)

Physical Description

Bushy-tailed woodrats are sexually dimorphic: adult males usually weigh 300-600 g with an average of 405 g, whereas adult females usually weigh only 250-350 g with an average of 270 g. These ranges are relatively large because this species occupies a large geographic range, and its body size is closely correlated with climate (conforms to Bergmann's rule). Neotoma cinerea is the largest and most cold-tolerant species of woodrat, and the largest and most sexually dimorphic individuals of this species are found in the northern parts of its range. In addition, body size of bushy-tailed woodrats (examined via fecal pellet size in middens) has been shown to correlate with known climatic fluctuations over the past 25,000 years. Woodrats are good climbers and have sharp claws. They have hypsodont molars with enamel ridges. The color of the pelage varies across the range, but is usually buff with white areas around the feet. The bushy tail characteristic of the species is used to warm the animal. Pictures of bushy-tailed woodrats are available in Vaughan (1990), Escherich (1981), and on the web at: http://darkstar.delta.dfg.ca.gov/gallery/woodrat.jpg. Escherich (1981) provides pictures of both sexes at various point throughout ontogeny, as well as pictures of skulls and skins.

(Egoscue, 1962; Escherich, 1981; Finley, 1990; Hickling et al., 1991; Martin, 1973; Smith, 1995; Smith et al., 1995; Vaughan, 1990)

  • Average mass
    335.5 g
    11.82 oz
    AnAge
  • Average basal metabolic rate
    1.152 W
    AnAge

Reproduction

Some aspects of the reproductive cycle of bushy-tailed woodrats are still under debate. These animals have been considered polygamous, polygynous, and/or promiscuous by various authors. Often these conclusions have been based not on actual observed matings, but on the size and relative overlap of male and female ranges. Breeding chiefly occurs in spring and summer (May through August). Females have small litters (up to six young at a time, though litter sizes over four tend to suffer losses since the female has only four mammary glands) but may have up to three litters per year. Modal litter size is three. Females have been observed breeding as soon as twelve hours after giving birth, and be may pregnant with one litter while nursing another. Males fight for access to mates, both through scent marking and actual physical contact. Fights consist largely of biting and scratching and may result in serious injury. Gestation period in captivity is 27-32 days. Newborns weigh approximately 15 g. Eyes open at around 15 days old, and weaning occurs at 26-30 days.

Males are heavier than females from early in development on. By weaning, males weigh 120-150 g, and females weigh 85-135 g. Females do not alter their foraging movements between pregnancy, lactation, and the post-reproductive period -- even though nutrient demands are higher at certain stages. Heavier females tend to have significantly more males in their litters than lighter females. Males are larger and require more energy to raise, though after weaning female offspring tend to reap more rewards from their mothers via philopatry (see "Behavior" section below). Females breed for the first time when they are yearlings.

(Egoscue, 1962; Escherich, 1981; Finley, 1990; Hickling et al., 1991; Moses and Millar, 1992; Moses et al., 1995; Topping and Millar 1996a; 1996b)

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • Average number of offspring
    3.68
    AnAge
  • Average gestation period
    30 days
    AnAge
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    353 days
    AnAge

Behavior

One of the most characteristic aspects of woodrat behavior is midden-building. Middens are often built in caves or crevices, and consist of plant material, feces, and other materials which are solidified with crystallized urine. Woodrat urine contains large amounts of dissolved calcium carbonate and calcium oxalates because of the high oxalate content of many of the succulent plants which make up the animals' diets. The mineralogical portion of the urine tends to crystallize over time, either within the midden or at specific "urinating posts" frequented by a number of animals over many years. An important distinction to make is between middens and nests. Nests are often within the midden, and are the area where the animal is often found and where females raise young. Bushy-tailed woodrats also build several food caches, which they utilize during the winter. These animals do not hibernate.

Bushy-tailed woodrats have fairly small home ranges. It was previously thought that they never ventured further than 60 m from their nests, but recent observations have shown that female N. cinerea may forage as far as 500 m from the nest. These animals are usually unsocial and solitary, nocturnal, and are strongly territorial. An exception is the relationship which sometimes develops between mothers and daughters. It is unclear whether mother-daughter pairs share nests, but they do have ranges with a high degree of overlap, and they do share resources. This seems to be beneficial to the daughter's survival (she benefits from the mother's food stores) and to the mother's reproductive success (perhaps because males are more likely to be attracted to a small area containing more than one female). Besides this mother-daughter bond, interactions between members of this species are overwhelmingly agonistic.

Much of the behavior of N. cinerea is thought to be a response to potential predation. Bushy-tailed woodrats are just the right size to be attractive to predators, including black bears, weasels, martens, bobcats, owls, and hawks. Nesting, nocturnal foraging, and small home ranges provide a degree of protection. Nesting also helps buffer the animal from temperature extremes.

(Cudmore, 1986; Emerson and Howard, 1978; Escherich, 1981; Finley, 1990; Frase and Sera, 1993; Moses and Millar, 1992; 1994; Smith et al., 1995; Topping and Millar, 1996a; Vaughan, 1990)

Communication and Perception

Food Habits

Because this species occupies such a wide range of habitats, its diet is variable. However, N. cinerea may best be described as a generalist herbivore. Most authors have considered it entirely herbivorous, though Johnson and Hansen (1979) believed a small component of its diet consists of arthropods. Bushy-tailed woodrats eat lots of woody vegetation, and in drier habitats also concentrate on succulents. This species gets all of its water from its food and does not need to drink. Woodrats tend to eat plant materials which have high concentrations of defensive chemicals; they combat these defenses by eating only small amounts of each species. Neotoma cinerea also tends to eat low-energy food items and plants which are high in oxalates. This has implications for the building of middens, discussed below. Neotoma cinerea has an enlarged caecum, and engages in coprophagy. Johnson and Hansen (1979) provide a list of specific food items utilized by this species in a cool, dry environment in Idaho.

(Escherich, 1981; Frase and Sera, 1993; Haufler and Nagy, 1984; Johnson and Hansen, 1979; Vaughan, 1990)

Economic Importance for Humans: Positive

Bushy-tailed woodrats are important to humans for several reasons. They are important to paleontologists and paleoclimatologists not only because their middens preserve easily-dated plant macrofossils, but also because this species incorporates lots of bones into its middens as well. Packrat middens are a major source of information about Pleistocene paleoclimates and paleoecology in the western United States.

Neotoma cinerea is also important as a prey species. For instance, the bushy-tailed woodrat is one of the major food items for northern spotted owls, a species which is in jeopardy because of range reductions due to logging. The carrying capacity of owls in a particular habitat is largely dependent upon the density of their prey. Interestingly, however, Neotoma cinerea is least frequent in old-growth forests, and found more frequently in more recently cut and open habitats.

(Frase and Sera, 1993; Rosenberg et al., 1994; Vaughan, 1990)

Economic Importance for Humans: Negative

Bushy-tailed woodrats are attracted to shiny items and often steal them from campsites or buildings. They can be a pest species throughout their range as they find a way into buildings and establish den sites.

Conservation Status

Neotoma cinerea is not in any danger, and I did not find any literature discussing the problems of conservation of this species.

Other Comments

Bushy-tailed woodrats are the hosts for a large number of parasites, and there is a literature on Neotoma parasites (e.g. Cudmore, 1986). In Oregon, for instance, a sample of bushy-tailed woodrats had 37 species of fleas, lice, ticks, and mites associated with them.

There is also a fairly extensive literature on packrat middens and their implications. One good source for this information is Betancourt, J.L., van Devender, T.R., and Martin, P.S. 1990. Packrat middens: the last 40,000 years of biotic change. University of Arizona Press, Tucson.

Finley's (1958) monograph on woodrats in Colorado (University of Kansas Publications, Museum of Natural History, 10: 213-552) contains large sections about N. cinerea. I did not use this source in preparing this account. Instead I at looked more recent literature, much of which cited and compared their results with those of Finley (1958).

Information on this species is also available on the web in a variety of locations, including http://www.fs.fed.us/database/feis/animals/Mammal/NECI/index.html and http://www.fw.vt.edu/fishex/nmex_main/species/050645.htm.

Contributors

Josh Trapani (author), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

taiga

Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

References

Cudmore, W.W. 1986. Ectoparasites of Neotoma cinerea and Neotoma fuscipes from western Oregon. Northwest Science, 60: 174-178.

Emerson, D.D. and Howard, W.E. 1978. Mineralogy of woodrat, Neotoma cinerea, urine deposits from northeastern California. Journal of Mammalogy, 59: 424-425.

Finley, R.B. 1990. Woodrat ecology and behavior and the interpretation of paleomiddens. in Betancourt, J.L., van Devender, T.R., and Martin, P.S. Packrat middens: the last 40,000 years of biotic change. University of Arizona Press, Tucson: 28-42.

Egoscue, H.J. 1962. The bushy-tailed woodrat: a laboratory colony. Journal of Mammalogy, 43: 328-337.

Escherich, P.C. 1981. Social biology of the bushy-tailed woodrat, Neotoma cinerea. University of California Publications in Zoology, 110: 1-132.

Frase, B.A. and Sera, W.E. 1993. Comparison between plant species in bushy-tailed woodrat middens and in the habitat. Great Basin Naturalist, 53: 373-378.

Grayson, D.K. and Livingston, S.D. 1989. High-elevation records for Neotoma cinerea in the White Mountains, California. Great Basin Naturalist, 49: 392-394.

Grayson, D.K., Livingston, S.D., Rockart, E. and Shaver, M.W. 1996. Biogeographic significance of low-elevation records for Neotoma cinerea from the northern Bonneville Basin, Utah. Great Basin Naturalist, 56: 191-196.

Haufler, J.B. and Nagy, J.G. 1984. Summer food habits of a small mammal community in the pinyon-juniper ecosystem. Great Basin Naturalist, 44: 145-150.

Hickling, G.J., Millar, J.S. and Moses, R.A. 1991. Reproduction and nutrient reserves of bushy-tailed wood rats (Neotoma cinerea). Canadian Journal of Zoology, 69: 3088-3092.

Johnson, M.K. and Hansen, R.M. 1979. Foods of cottontails and woodrats in south-central Idaho. Journal of Mammalogy, 60: 213-215.

Martin, R.J. 1973. Growth curves for bushy-tailed woodrats based upon animals raised in the wild. Journal of Mammalogy, 54: 517-518.

Mewaldt, W.T. 1982. Biochemical variation in two species of Great Basin rodent. Mammalian Chromosomes Newsletter, 23: 34. (abst.)

Moses, R.A., Hickling, G.J. and Millar, J.S. 1995. Variation in sex ratios of offspring in wild bushy-tailed woodrats. Journal of Mammalogy, 76: 1047-1055.

Moses, R.A. and Millar, J.S. 1992. Behavioural asymmetries and cohesive mother-offspring sociality in bushy-tailed wood rats. Canadian Journal of Zoology, 70: 597-604.

Moses, R.A. and Millar, J.S. 1994. Philopatry and mother-daughter associations in bushy-tailed woodrats: space use and reproductive success. Behavioral Ecology and Sociobiology, 35: 131-140.

Rosenberg, D.K., Zabel, C.J., Noon, B.R., and Meslow, E.C. 1994. Northern spotted owls: influence of prey base - a comment. Ecology, 75: 1512-1515.

Smith, F.A., 1995. Scaling of digestive efficiency with body mass in Neotoma. Functional Ecology, 9: 299-305.

Smith, F.A., Betancourt, J.L., and Brown, J.H. 1995. Evolution of body size in the woodrat over the past 25,000 years of climate change. Science, 270: 2012-2014.

Topping, M.G. and Millar, J.S. 1996a. Foraging movements of bushy-tailed woodrats (Neotoma cinerea). Canadian Journal of Zoology, 74: 798-801.

Topping, M.G. and Millar, J.S. 1996b. Spatial distribution in the bushy-tailed woodrat (Neotoma cinerea) and its implications for the mating system. Canadian Journal of Zoology, 74: 565-569.

Vaughan, T.A. 1990. Ecology of living packrats. in Betancourt, J.L., van Devender, T.R., and Martin, P.S. Packrat middens: the last 40,000 years of biotic change. University of Arizona Press, Tucson: 14-27.