Peromyscus keeni
northwestern deermouse

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)

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)

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, Ricci, and Hyelle, 2001; Podlutsky et al., 2008; Ribble, 2003)

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)

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)

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, Metheny, and Vonhof, 2006)

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, Ryder, and Bertram, 1999; Bradley and Marxluff, 2003; Drever et al., 2000; Hanley and Barnard, 1999b; Reese, Barnard, and Hanley, 1997)

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, Flynn, and Schell, 1996)

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, Ryder, and Bertram, 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)

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)

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. (Podlutsky et al., 2008; Vrana, 2007)

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)

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)