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Peromyscus maniculatus - Deer Mouse

Description:

Peromyscus maniculatus, commonly known as the deer mouse, ranges in size from 120 to 165 mm long and from 10 to 24 g in weight (Kurta 1995).  It has a slender, yet cylindrical body shape, with large ears ranging from 12 to 21 mm in height, that are rimmed in white fur.  Its colors range from grayish to reddish brown, with a black band running down the dorsal midline of its body and a white ventral surface.  Its fur is short, soft, and dense.  The length of its tail can vary depending on population and range, from 42 mm to 110 mm (Kurta 1995).  Deer mice have tails that are covered in fine hair, and are darker in color on the top, which contrasts with the obvious light color of their under surface.  This contrast differs from the other species of Peromyscus, P. leucopus, where the separation of the dark and light colors of the tail is less apparent and more gradual.

In addition to tail color, there are other features that help one discern Peromyscus maniculatus from Peromyscus leucopus, or the white-footed mouse.  P. maniculatus has hind feet that are typically 15 to 19 mm in length, while P. leucopus usually has hind feet that are 22 mm or more in length.  Deer mice have a more distinct tail tuft than white-footed mice as well.  P. maniculatus also tends to be darker brown in color with a lesser defined middorsal band, while P. leucopus is tanner, or grayish, in color with intermingling dark hair (Kurta 1995).  P. maniculatus has shorter forelimbs than hind limbs and has a dental formula of I 1/1 C 0/0 P 0/0 M 3/3 = 16 (Baker 1983).  Its molars are low-crowned and cuspidate, and the third upper molar is less wide than the first two.  This is another characteristic that differs in P. leucopus, whose third upper molar is approximately as wide as the first two (Baker 1983).

Distribution in Wisconsin:

Two Peromyscus subspecies that are found in Wisconsin include Peromyscus maniculatus gracilis and Peromyscus maniculatus bairdii.  P. m. gracilis can be found in forested or shrubby areas, while P. m. bairdii is found mainly in open areas, such as meadows, cultivated fields, pastures, and sand dunes along lake shores.  P. m. gracilis and P. m. bairdii are easily distinguished from one another.  P. m. gracilis has a longer tail, ears, skull, and hind feet than P. m. bairdii.  Although these two subspecies have overlapping ranges in Wisconsin, they do not interbreed.  One possible explanation for this could be that habitat preference, forest or prairie, limits their contact (Baker 1983).  In a study published in 1997, researchers studied two species of Peromyscus, and found that interspecific interactions between these species were rare, and that natural niche segregation was common between the two species (Songer et. al. 1997).

Peromyscus maniculatus distribution extends beyond Wisconsin, and it occupies many different ecological zones throughout its range. Deer mice can be found in many different habitats, including:  alpine areas, northern boreal forest, desert, temperate grassland, brushland, southern montane woodland, and tropical habitats.  Their most common habitats include prairie and woodland, which is why they are abundant across Wisconsin, inhabiting deciduous, coniferous, and mixed forests.

They are often found in manmade buildings as well, residing in old sawmills, shacks, and cabins.  Home ranges of Peromyscus maniculatus can vary from 242 square meters to 3000 square meters.  On average, home ranges of males are larger than that of females and show more overlap.  They are an abundant species, with densities that can reach up to 11 mice per acre (Baker 1983).  Quantity and quality of foods, water, and nest site availability are some of the ecological factors that can affect the density of P. maniculatus.  It is interesting to note that only the availability of food has been studied in enough detail to show it has an effect on P. maniculatus population density (Kirkland, et. al. 1989).

Ontogeny and Reproduction:

Peromyscus maniculatus females are seasonally polyestrous, with an estrous cycle of five days on average, typically beginning in March (Kurta 1995).  In cooler climates, reproduction may not occur during until April or May when environmental conditions are optimal and food is plentiful (LTER 1998).  Females also exhibit estrus immediately after giving birth, and are able to become pregnant shortly after a litter has been born, in fact as early as 35 days after weaning. The gestation period of a non-lactating female deer mouse lasts from 22 to 25 days, while a lactating female has a gestation period of 24 to 30 days (Kirkland, et. al. 1989).  In a recent study, it was found that deer mice responded to increased energetic demands, such as lactation or cold exposure, by increasing their digestible food intake and by increasing the sizes of their digestive organs.  The study also found that heart mass was lower in lactating than in non-lactating mice, and it was concluded that deer mice are not limited by central processing organs because they are able to increase digestive organ size continuously with increased energetic demands (Hammond et. al. 2000).

Litter size is also extremely variable between Peromyscus maniculatus populations.  Some populations may have litters containing from one to eight young, with typical litters containing four to six individuals (Baker 1983).  Litter size will increase with each birth until the fifth or sixth litter, and will then begin to decrease for future litters (LTER 1998).  A female can have four litters or more during a year with a warm winter. A study done by Kalcounis-Rueppell, et. al., examined how climate can limit seasonal breeding in populations of P. maniculatus (Kalcounis-Rueppell, et. al. 2002).  The researchers found similar results to Hammond, et. al., in that compensatory response, such as increasing or decreasing organ size, appears sufficient enough to counter extreme weather conditions during breeding and non-breeding seasons (Hammond, et. al. 2000).

Peromyscus maniculatus young are altricial at birth, but will develop quickly.  At birth, a deer mouse has a mass of about 1.5 g.  It is born hairless, with wrinkled, pink skin, closed eyes, and with ear pinnae that are folded over.  Juvenile hair begins to develop on the second day after birth, and on the third day, the pinnae unfold.  The ear canals will not open until the tenth day, its eyes will open on the fifteenth day, and it will be weaned between day 25 and 35.  The first estrus typically occurs around 49 days in most deer mice (King 1968).

The tiny pink babies are blind for the first two weeks of their lives.  During this time they often remain firmly attached to their mother’s teats for nourishment and protection.  While the mother is nursing, she will carry her young one at a time in her mouth or move with them clinging to her nipples (Baker 1983).  After they have been weaned, at around five weeks after birth, the young deer mice usually leave the nest and become independent.  Sometimes, however, the mother may tolerate their presence for longer periods, but usually when the mother is about to have her second litter, she will force the first litter out of the nest (King 1968).  Captive Peromyscus maniculatus have been known to live up to eight years; however most wild deer mice can only survive up to 10 to 12 months (Kurta 1995).

Ecology and Behavior:

As a nocturnal species, Peromyscus maniculatus’ biggest predators include snakes, owls, and a variety of other large, nocturnal mammals.  Woodland deer mice spend most of their time on the ground, but they are also adapted to climbing, and may spend as much time in the trees as they do on the ground (Kurta 1995).  The majority of their activity centers on their nest and their main food source.  In terrestrial prairie subspecies, such as in P. m. bairdii, a baseball-sized nest is constructed just below ground level in a small constructed burrow or in one that has been abandoned by another animal.  Forest dwelling subspecies, like P. m. gracilis, construct nests near the ground in stumps, logs, tree cavities, reconstructed bird nests, or in buildings.

Nests are typically made of rounded masses of vegetation and lined with bits of fur, feathers, or shredded grasses and they are usually around 100 mm in diameter (Kurta 1995).  A pregnant female builds the spherical pile when the young are about to be born.  She will use the nest for about a month while she rears her young, and then move on to another site.  Males will build nests throughout the year as well, changing sites as their home fills with feces and urine, all of which is deposited in the nest.

Peromyscus maniculatus nests can be distinguished, if you have a little patience.  Over the course of a week or two, listen for the tiny, almost inaudible squeaks of the young coming from the cavity.  It’s not uncommon for the adult mouse to sense your presence and silence the newborns; however, if you don’t hear anything from the nest after two weeks of listening, you most likely have a male nest or an abandoned nest left behind for another site.

Reproductive females exhibit territory defense much more aggressively than males.  Female territories overlap less as well, suggesting that they have a greater investment in territory defense than males.  In fact, infanticide has been known to occur in Peromyscus maniculatus when young are being unattended by their mother (Kirkland, et. al. 1989).  P. maniculatus is polygynous, where a mature male, a few mature females, and several young constitute the basic social unit.  It normally lives alone during warmer months, however in the winter, groups of individuals of mixed sexes and ages may huddle together in communal nests to increase their surface area and conserve heat.  Also during winter, P. maniculatus will forage above and below snow, and may enter into a daily torpor to reduce body temperature and conserve energy (Kurta 1995).  In 2001, Davidson, et. al., conducted a study whereby they found that P. maniculatus increased its foraging activity and its harvest rates when population densities were reduced, which emphasizes the importance of competition in the behavior of deer mice (Davidson, et. al. 2001).

Peromyscus maniculatus is omnivorous.  It is mainly nocturnal and depends heavily on olfaction for locating its food.  It will eat a wide array of plant and animal matter depending on what is readily available.  Its diet may include: insects and other invertebrates, seeds, fruits, flowers, nuts, or other plant products.  Even during winter months 15 to 55% of its diet will consist of animal flesh (Kurta 1995).  Deer mice will exhibit coprophagy on certain occasions as well.  In cooler climates, such as in Wisconsin, P. maniculatus will cache food in secret granaries during the autumn months to store for winter when fresh food is scarce (Baker 1983).

Remarks:

Peromyscus maniculatus is called a deer mouse because the coloring of its fur resembles that of a deer, having dark on the dorsal surface, and white on the legs and underside.  Its tails are also dark on top and white underneath, similar to that of a deer’s tail.  The scientific genus name for deer mice is somewhat bewildering.  Pero is Greek for defective, and myscus is derived from the Greek word, myskos, meaning mouse.  The species name, maniculatus, is Latin for little hand.

Peromyscus maniculatus is both beneficial and costly to other organisms.  It does provide food for carnivores, including hawks and owl species in Wisconsin, and deer mice also consume some insects that are considered pests (Baker 1983).  They may also help disperse the seeds of a number of plants species, as well as the spores of mycorrhizal fungi.  On the other hand, woodland deer mice consume seeds of valued forest trees, sometimes preventing forest regrowth.  In addition, P. maniculatus can be destructive by consuming stored grains and other food, by gathering litter in buildings, and by gnawing through wood and clothing (Baker 1983).

Finally, Peromyscus maniculatus is the host for a strain of hantavirus called Sin Nombre Virus.  This virus, which can be contracted by humans from deer mice, can cause a potentially fatal disease termed Hantavirus Pulmonary Syndrome (Shope 1999).  Deer mice feces, urine, and saliva can carry hantavirus, which causes a respiratory illness that has sickened and killed people.  Symptoms of Sin Nombre Virus include fever, chills, occasional headaches, and possible digestive problems.  After a short period of time, breathing problems can occur, including coughing and shortness of breath.

Literature Cited:

Baker, R. H.  1983.  Michigan Mammals. Wayne State University, Detroit.

Davidson, D.L. and D.W. Morris.  2001.  Density-dependent foraging effort of Deer Mice, Peromyscus maniculatus.  Functional Ecology 15:  575-583.

Hammond, Kimberly A. and Deborah M. Kristan.  2000.  Responses to lactation and cold exposure by deer mice (Peromyscus maniculatus).  Physiological and Biochemical Zoology 73:  547-556.

Kalcounis-Rueppell, Matina C., John S. Millar, and Emily J. Herdman.  2002.  Beating the odds:  Effects of weather on short-season populations of deer mice.  Canadian Journal of Zoology 80:  1594-1601.

King, J. A.  Biology of Peromyscus.  1968.  The American Society of Mammalogists.  Stillwater.

Kirkland, G. L. and J. N Layne.  1989.  Advances in the Study of Peromyscus.  Texas Tech University Press, Lubbock.

Kurta, Allen.  1995.  Pp. 153-156 in Mammals of the Greats Lakes Region.  University of Michigan Press, Ann Arbor.

“LTER:  Sevilleta Long-Term Ecological Research Project.”  1998.  University of New Mexico.  <http://sevilleta.unm.edu/data/species/mammal/profile/deer-mouse.html>.  Accessed 28 Oct. 2003.

Shope, Robert E.  1999.  A midcourse assessment of hantavirus pulmonary syndrome.  Emerging Infectious Diseases 5:  172-174.

Songer, M.A., Mark V. Lomolino, and David R. Perault.  1997.  Niche dynamics of deer mice in a fragmented, old-growth-forest landscape.  Journal of Mammalogy.  78:  1027-1039.

Reference written by Brianna Schoessow, Biology 378 student.  Edited by Christopher Yahnke. Page last updated 4-29-04.

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