Peromyscus keeninorthwestern deermouse

Geographic Range

Peromyscus keeni is found in western British Columbia, western Washington, and southeastern Alaska, including the Haida Gwaii (Queen Charlotte) islands, the Alexander Archipelago, and other coastal islands. (Linzey and Hammerson, 2008; Musser and Carleton, 2005)


Northwestern deer mice are adapted to many habitats, but appear to thrive in upland and new-growth forests. They also commonly inhabit old-growth forests and floodplains, although those are less favorable because they lack the spatial and temporal complexity that promotes survivorship. They are found in rainy areas with mild climates and semi-open canopies. They are found at higher elevations than Peromyscus maniculatus in the same region. On small islands, northwestern deer mice are found along the edges of cedar-spruce forest and on beaches where logs, rocks, and debris provide sufficient cover. (Linzey and Hammerson, 2008; Lomolin and Perault, 2007; Smith and Nichols, 2004; Van Zant and Wooten, 2007)

Physical Description

Northwestern deer mice are medium sized cricetids. Juveniles are a grayish color, while adults are tri-colored. They are brown dorsally and light grey ventrally with tails that are brown dorsally and white ventrally. Northwestern deer mice have long tails (more than 100 mm) and large, naked ears. The tail is slender with short hair and is distinctly bi-colored. Peromyscus keeni is distinguishable from P. maniculatus because of its darker fur color and longer tail (tail length in P. maniculatus is less than 100 mm). Body size in northwestern deer mice is significantly correlated with elevation, with body size peaking at intermediate elevations. (Lomolin and Perault, 2007; Musser and Carleton, 2005)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    10 to 30 g
    0.35 to 1.06 oz
  • Range length
    181 to 236 mm
    7.13 to 9.29 in


There is no available information on mating systems in northwestern deer mice. Mating systems in Peromyscus are variable, and include monogamous, roving, or polygynous mating behaviors. At high female densities, males become more territorial and defend a small number of females or maintain a monogamous relationship with one female. In areas with low female densities, females become solitary and males develop a less territorial, roving strategy where they mate with multiple females. Females generally maintain small, solitary home areas in all mating systems. (Nichol, et al., 1993; Ribble, 2003; Linzey and Hammerson, 2008; Nichol, et al., 1993; Ribble, 2003)

During the breeding season, northwestern deer mice females with mates have short breeding intervals and exhibit postpartum estrus. Breeding intervals are increased among females that do not have established mates. In wild populations, many adults only live long enough to reproduce during one breeding season. Adult males enter breeding condition prior to adult females and all females average 2 to 3 litters per breeding season. Females give birth to 2 to 5 young after a gestation period of 23 to 25 days. Gestation periods are shorting when females are nursing a previous litter. Litter size is positively correlated with relative litter mass: larger litter sizes result in smaller body sizes of young in that litter. Young are weaned and independent at 3 to 4 weeks old and may be able to breed as early as 5 to 6 weeks old. Males have a lifetime reproductive success that is twice that of females. (Kenagy and Barnes, 1988; Linzey and Hammerson, 2008; Morrison, et al., 1976; Ribble, 2003)

  • Breeding interval
    Female northwestern deer mice breed two to three times per breeding season.
  • Breeding season
    Breeding occurs from February to October.
  • Range number of offspring
    2 to 5
  • Average number of offspring
  • Range gestation period
    23 to 25 days
  • Range weaning age
    3 to 4 weeks
  • Range time to independence
    3 to 4 weeks
  • Range age at sexual or reproductive maturity (female)
    5 to 6 weeks
  • Range age at sexual or reproductive maturity (male)
    5 to 6 weeks

Parental investment in northwestern deer mice has not been well-studied. Like all mammals, females invest substantially in young through gestation and lactation. (Botten, et al., 2001; Ribble, 2003)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female


Little research has been conducted on the lifespan of northwestern deer mice. Related species (P. maniculatus, P. californicus, and P. leucopus) have expected lifespans in the wild of 342.2 days for males and 280.9 days for breeding females. Some individuals survive to reproduce for a second breeding season. (Botten, et al., 2001; Ungvari, et al., 2008; Ribble, 2003)

  • Range lifespan
    Status: wild
    3 (high) years
  • Average lifespan
    Status: wild
    1 years


Northwestern deer mice are nocturnal and have a more loosely structured social hierarchy than some of their sister taxa. A rapid growth rate, larger litter sizes, and simple nests contribute to their social structure difference. Males exhibit severe aggression when confronted by other males. Males show aggression towards other males in their territory, submission when in a new territory, and are more prone to initiate grooming when encountering new females. Females show no defensive behavior around their nest unless they are pregnant. In some instances females will share their nest with their younger, reproducing female offspring. (Eisenberg, 1962; Hanley and Barnard, 1999a; Ribble, 2003)

  • Average territory size
    2,678 m^2

Home Range

Territoriality in northwestern deer mice is dependent on population density. In a heavily populated area males will have relatively small territories, while in a low density area they maintain larger territories. Females typically maintain smaller territories that overlap with the territories of several males. (Eisenberg, 1962; Hanley and Barnard, 1999a; Ribble, 2003)

Communication and Perception

Rodents rely heavily on their sense of olfaction to interact within their social hierarchies. Dominance can be conveyed to other members of the community solely by odor. A recent topic of interest for research is rodent ultrasound. Ultrasonic vocalizations have been observed in research mice as well as in wild populations of P. californicus and P. boylii. Based on literature on other mammal and bird ultrasound, it is likely that this method of communication is used by all Peromyscus species to communicate with offspring, maintain territory boundaries, and to communicate with as well as attract mates. It is unlikely that ultrasonic vocalizations are used as a alarm calls as this behavior is only known from diurnal animals. (Kalcounis-Rueppell, et al., 2006)

Food Habits

Northwestern deer mice are mainly granivorous ground foragers. In an intake preference study done on foods from southeastern Alaska seeds from trees, shrubs and fruits were compared as well as fruits for palatability. It was found that salmonberry, stink currants, devil's club seeds, and Sitka spruce seeds were preferred. When diet composition in different ecological habitats was compared, stomach contents did not vary significantly. All diets were composed mostly of fruits and seeds of understory plants, followed by tree seeds and leaf material, with small amounts of arthropods and traces of fungi. Tree seeds become a more important part of their diets during winter and early spring because these mice do not cache food or store seasonal fat. In some areas they eat the eggs of nesting birds, including marbled murrelets (Brachyramphus marmoratus) and rhinoceros auklets (Cerorhinca monocerata). (Blight, et al., 1999; Bradley and Marxluff, 2003; Drever, et al., 2000; Hanley and Barnard, 1999b; Reese, et al., 1997)

  • Animal Foods
  • birds
  • fish
  • eggs
  • carrion
  • insects
  • terrestrial non-insect arthropods
  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • fruit
  • Other Foods
  • fungus


Primary predators are American martens (Martes americana), owls (Strigidae), red foxes (Vulpes vulpes). Other terrestrial predators are likely to take northwestern deer mice and their young, including large snakes, other raptors, and weasels (Mustela). Northwestern deer mice are cryptically colored and secretive to avoid predation. (Ben-David, et al., 1996)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Northwestern deer mice influence seabird populations in coastal areas by preying on their eggs and nestlings. Marbled murrelet (Brachyramphus marmoratus) and rhinoceros auklet (Cerorhinca monocerata) are preyed on by these mice. In one study area, 34% of rhinoceros auklet eggs had been preyed on by northwestern deer mice. Predation occurs mostly during the early post-laying period when adults are foraging and occurs minimally in later incubation and hatchling periods. If food sources for the rhinoceros auklets become limited their foraging time increases, which puts their eggs at an even greater risk for predation. (Blight, et al., 1999; Bradley and Marxluff, 2003; Drever, et al., 2000)

Seed dispersal mutualism has been suggested between Peromyscus maniculatus and limber pine (Pinus flexilis). Other Peromyscus species may drive seed defense evolution through their secondary dispersal effects, causing the method of seed dispersal which plants rely on to change in the presence of ground scavengers. (Siepielski and Benkman, 2008)

Peromyscus keeni can be a host to several invertebrate parasites such as lice, ticks, bots and fleas. The flea species that are known to use P. keeni as a host are: Hystrichopsylla occidentalis, Catallagia charlottensis, Ceratophyllus ciliates protinus, Megabothris abantis, Opisodasys keeni, and Malaraeus telchinus. (Haas, et al., 2005)

  • Ecosystem Impact
  • disperses seeds
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Species in the genus Peromyscus are useful for the research of genomic imprinting. Peromyscus has been an important model for showing an X-linked locus in hybrid dysgenesis when crossing different species. They have also been used for researching reproductive isolation in mammals. Peromyscus have a much longer lifespan than typical lab mice, making them useful for many forms of research. The longevity of Peromyscus has been analyzed as baseline research for comparative aging research. Their physiological characteristics may help us understand and treat age-related diseases such as cancer. (Ungvari, et al., 2008; Vrana, 2007)

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

Peromyscus maniculatus is a natural reservoir for Lyme disease and hantavirus. Peromyscus keeni may also transmit these pathogens and negatively affect human health. Northwestern deer mice may also enter homes and become a nuisance. (Nichol, et al., 1993; Stafford, et al., 1999)

  • Negative Impacts
  • injures humans
    • carries human disease
  • household pest

Conservation Status

Peromyscus keeni is listed as “least concern” by the IUCN because of their widespread, stable populations and adaptability to various habitats. (Linzey and Hammerson, 2008; Smith and Nichols, 2004)

Other Comments

Peromyscus keeni includes the previously recognized species Peromyscus keeni oreas and Peromyscus keeni sitkensis as well as some populations previously recognized as Peromyscus maniculatus (P. m. algidus, P. m. hylaeus, P. m. keeni, P. m. macrorhinus, and P. m. prevostensis). It is possible that 3 other P. maniculatus subspecies should be included in P. keeni: P. m. carli, P. m. doylei, and P. m. triangularis. (Linzey and Hammerson, 2008; Musser and Carleton, 2005)

A health condition of the genus Peromyscus that is prevalent at a similar rate in humans is periodontal disease. Peromyscus keeni exhibited this disease at rates between 7 and 13.5%, with a significantly increased rate in populations on isolated islands. This condition occurs rarely in any other mammalian species, which may make Peromyscus a valuable research model. (Wiebe, et al., 2001)


Tanya Dewey (editor), Animal Diversity Web.

Kimberly Dullen (author), University of Alaska Fairbanks, Hayley Lanier (editor, instructor), University of Alaska Fairbanks .



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


uses sound to communicate


young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

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.


flesh of dead animals.


uses smells or other chemicals to communicate


the nearshore aquatic habitats near a coast, or shoreline.


having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.


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


an animal that mainly eats seeds


An animal that eats mainly plants or parts of plants.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


having the capacity to move from one place to another.

native range

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


active during the night


an animal that mainly eats all kinds of things, including plants and animals


rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.


Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season


remains in the same area


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


associates with others of its species; forms social groups.


lives alone


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.


defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement


uses sound above the range of human hearing for either navigation or communication or both


uses sight to communicate


reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.


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