Peromyscus polionotus
Oldfield mouse

by Dr. Michael C. Wooten, Dept. of Zoology, Auburn University.

GENERAL STATEMENT
Peromyscus polionotus is the smallest species of the genus in the United States. P. polionotus is widely distributed within the southeastern United States.   The species is confined to sandy dry soils where it can construct characteristic burrows.

DESCRIPTION
Pelage: Color varies greatly and is correlated with substrate color.  Inland forms exhibit dark brown to wood brown dorsal areas and sides with distinct ventral boundary.  Undersides of body and tail are pure white. Tail is bicolored with a variable dark stripe on dorsal surface.  Manus and feet are white (Huestis, 1932; Howell, 1939; Bowen and Dawson, 1977; Kaufman, 1974).
Size: Smallest of the North American Peromyscus, tail is short usually 55-65% of body length (Blair, 1968).
Weight: Ranges from 10.0 to 17.0 g.   Males are generally smaller than females with pregnant females reaching 22 - 25g.
Measurements: Total length is 122 to 153 mm; length of tail, 40 to 60; hind foot, 15 to 19; ear from notch, 11.6 to 16.5; greatest length of skull, 22.5 to 23.5; zygomatic width, 12.2 to 13.0; interorbital constriction, 3.7 to 3.9; length of nasals, 8.8 to 9.7;  and length of maxillary toothrow, 3.3 to 3.4. mm (Howell,1939; Hall, 1981).

FORMAL DIAGNOSIS
Total length is 122 to  153 mm; tail is shorter than head and body, commonly bicolored, but varies within and among subspecies.  Color is generally dark brown above with pure white undersides and feet;  color is geographically variable and correlated with soil or leaf litter; coastal subspecies show marked variation and reduction in pelage color, ranging from dark brown to cinnamon to pale white; variation in extent of dorsal coloration onto ears, head and rump is common subspecies diagnostic.

The skull is much smaller than P. maniculatus or P. gossypinus; auditory bullae are slightly larger and inflated (Hall, 1981).  Baculum is vase shaped; its base is broad, flat, widest near middle, its shaft is straight and relatively small; bacular length averages 6.5 mm; width of base averages 1.0 (Blair, 1942:197).

DISTRIBUTION
P. polionotus is widely distributed throughout the southeastern United States (Hall, 1981).  Beginning in extreme southwestern North Carolina, the range of the Oldfield mouse is reported to include western South Carolina, all of Georgia (excluding northern mountains and extreme southeastern wetlands), all of eastern/central Alabama, extreme northeastern Mississippi and northern / central Florida. Coastal subspecies are found on islands and frontal dune habitats from Fort Morgan in Mobile Bay, Alabama east and southward to the St. Joseph peninsula in Florida.  Three coastal subspecies (one extinct) are also found along the Atlantic coast of Florida from Brevard County northward to St. Johns.  Populations of P. polionotus are generally limited to sandy soils most often associated with open sandy ridges (relic dune systems).

HABITAT
P. polionotus is an early succession specialist that reaches greatest densities in open sandy areas.  The species is an early succession specialist often invading disturbed habitat, hence the common name "Oldfield Mouse".   In these areas, the populations tend to persist for 3-5 years before being once ground cover becomes dense.  In coastal habitats, P. polionotus is often the only species of small mammal to be a permanent resident of the highly dynamic frontal dunes.  Local densities can become large in these habitats (18 - 26 mice per ha; Lynn, 2000).  In the central portion of its range, P. polionotus can be found in pockets of low density in mixed pine-hardwood forests where the canopy is open and the understory sparse.  Roadway shoulders are also used effectively as habitat by this species.

Home range estimates for P. polionotus vary among studies and appear to be correlated with food or burrow site availability (Smith, 1971; Lynn, 2000).  Davenport (1964), using trapping data, estimated mean home range size to be 1376 m2  for Oldfield mice while Novak (1997) reported a substantially larger value of 3168 m2  for home ranges of P. p. allophrys on Shell Island Florida.  Average values reported by Lynn (2000) for Alabama beach mice, P. p. ammobates, were 4086 - 5512 m2  from trapping data and 6783 - 7000 m from telemetry data.  Home ranges also vary according to season and reproductive state of the mice.  Values as small as 389 m2  and as large as 29,330 m2  have been observed (Lynn, 2000).   Home range sizes do not differ significantly between males and females.

NATURAL HISTORY
The Oldfield mouse is a small, semi-fossorial, nocturnal rodent endemic to the southeastern United States.  The presence of this species is characterized by scattered burrow openings with fan shaped sand plumes, most often on sparsely vegetated sandy slopes.  P. polionotus are extremely curious and easily live-trapped.  Multiple captures of a single mouse in one night are common.  This species is only rarely found associated with human dwellings.

The burrowing habits and burrow structure of P. polionotus was described by Sumner and Karol (1929), Hayne (1936) and Blair (1951).  Burrows typically consist of an entrance tube up to 1 m deep leading to one or more chambers (mean depth = 53 cm; Smith, 1966).  An escape tunnel is normally present from the nest chamber to just below the surface.  Total volume of the average burrow is 4,046 cc (Smith, 1966).   Nests of dried grasses and other fibers are found in the central chamber.  Burrows are usually located on higher areas of sandy slopes or beach dunes in well drained soils. Burrow openings are frequently located within vegetation.  A fan-shaped plume of expelled sand is characteristic of active burrows.  Entrance tunnels are blocked several centimeters below the surface by sand plugs, presumably for predator defense.  Oldfield mice have been reported to have up to 20 burrows within their home range (Blair, 1951) although 4 to 6 is more common.  The mice move among burrows on a fairly regular basis with movements more limited when litters are present.  Smith (1966) recorded 25 species of invertebrates/vertebrates in P. polionotus burrows from central Florida.

P. polionotus are carnivore-omnivore rodents with a majority of their diet being seasonal seeds (Gentry and Smith, 1968; Smith, 1971; Moyers, 1996).  Coastal populations concentrate on wind-deposited seeds such as sea oats and bluestem. Acorns form a significant portion of the diet for both inland and coastal forms when available.  Oldfield mice will also consume a variety of animal foods. Gentry and Smith (1968) documented the use of both insects and vertebrates, including a preference for animal foods over most seeds.  Insects consumed include beetles, leaf hoppers, true bugs, and ants (Moyers, 1996).

P. polionotus are nocturnal with daytime activity rare. Nightly movements are directly affected by weather conditions (Blair, 1951; Gentry and Odum, 1957; Wolfe and Summerlin, 1989).  Blair (1951) reported that Santa Rosa beach mice were trapped less often on nights with half to full moons and clear skies, and that mice rarely left their burrows during nights with full moons.  Wolfe and Summerlin (1989) conducted enclosure studies with P. p. rhoadsi and found that they decreased their activity by approximately 70 percent during full moon.  Gentry and Odum (1957) showed that increased captures of Oldfield mice occurred on warm cloudy nights and when conditions changed from clear to cloudy.  Recent radio tracking studies indicate that while active throughout the night, peaks of activity occur shortly after dusk and again after midnight.

While P. polionotus are capable of dispersing over 5 km (Smith, 1968) and commonly traverse 0.5 km of habitat per night, most observations indicate that individuals settle with a few hundred meters of their natal sites.  Swilling and Wooten (2002) report that juveniles disperse an average of 160 m, effectively one home range, away from the natal site.  Interestingly,  mice that dispersed greater than one home range exhibited a significantly longer persistence time (+ 37.5 d).  Dispersal distances for juvenile male and female P. polionotus have not been reported to differ.  In general, P. polionotus populations show little evidence of intraspecies competition with increasing densities yielding increased compaction of home ranges.  This combination of tolerance and dispersal results in the formation of spatial "neighborhoods" within populations.  For Alabama and Perdido Key beach mice, the approximate size of these spatial units is 550 m (linear) with occupancy by 40 - 70 mice.

The Oldfield mouse is well documented as one of the few monogamous species in the genus Peromyscus (Blair, 1951; Smith, 1966; Foltz, 1981; Swilling and Wooten, 2002).  Pair bonding is strong and parental cooperation in rearing has been noted (Margulis, 1997; 1998).  Litter sizes ranges from 2 to 8 (mode = 4; Caldwell and Gentry, 1965; Carmon et al., 1967).   The gestation period of P. polionotus averages 28 days with a post-partum estrus common.  Smith (1966) reported that one captive female beginning at 118 days of age gave birth to 26 consecutive litters (139 young) with an average inter-litter interval of 30 days.  Reproduction occurs throughout the year but typically slows during summer and peaks during late fall / early winter in correlation with availability of forage seeds.

The average life span of P. polionotus in natural populations is less than 9 months although it is not uncommon to encounter mice that are 1 year of age.   Captures of mice known to be 2 years old have been reported and captive P. polionotus have reached 4+ years of age.

Species reported to prey on P. polionotus include red and gray fox, owls, great blue heron, weasel, skunk, raccoon, various snakes including coach-whip, pygmy and diamondback rattle snakes, domestic dogs and domestic cats (Blair, 1951; Bowen, 1968, Holler, 1992).

KARYOLOGY
P. polionotus has the common diploid chromosome number for Peromyscus (2N= 48; Hsu and Arrighi, 1968; Te and Dawson, 1971).   Hsu and Arrighi (1968:430) reported the chromosome composition as  "five pairs of large and medium-sized biarmed elements, six pairs of small biarmed elements, and 12 pairs of acrocentrics".   The X chromosome was described as a large sub-metacentric and the Y chromosome as an acrocentric of medium size.

CLASSIFICATION
Order Rodentia, Suborder Myomorpha, Family Muridae, Subfamily Sigmodontinae, Tribe Peromyscini, Genus Peromyscus, Subgenus Peromyscus, maniculatus-species group.

TAXONOMIC HISTORY
Mus polionotus, Wagner, 1843. Type locality Georgia.
Peromyscus subgriseus, Bangs, 1898:202.
Peromyscus polionotus, Osgood, 1907, first use of current name combination.

SUBSPECIES
* From Hall, E. R. (1981), Mammals of North America

P. p. albifrons, Osgood, 1909:108.  Type locality Whitfield, Walton County. Florida.

P. p. allophrys, Bowen, 1968:18. Type locality Walton County, Florida.
                          Endangered
                          Choctawhatchee beach mouse.

P. p. ammobates, Bowen, 1968:16. Type locality near Alabama Point, Baldwin County, Alabama.
                         Endangered
                          Alabama beach mouse .

P. p. colemani, Schwartz, 1954:566. Type locality Campton, Spartanburg County, South Carolina.

P. p. decoloratus,  Howell, 1939:363. Type locality Mosquito Inlet, VolusiaCounty, Florida.
                         Presumed Extinct
                          Pallid beach mouse

P. p. griseobracatus, Bowen, 1968:16. Type locality Navarre, Santa Rosa County, Florida.

P. p. leucocephalus,  Howell, 1920:239. Type locality Santa Rosa Island, Okaloosa County, Florida.
                        Santa Rosa beach mouse

P. p. lucubrans,  Schwartz, 1954:564. Type locality Allendale County, South Carolina.

P. p. niveiventris,  (Chapman), 1889:117. Type locality Micco, Brevard County, Florida.

Hesperomys noveiventris,  Chapman, 1989

P. p. niveiventris, Osgood, 1909:105.
                        Threatened
                         Southeastern beach mouse

P. p. peninsularis,  Howell, 1939:364. Type locality St. Andrews Point, Bay County Florida.
                        Endangered
                         St. Andrews beach mouse.

P. p. phasma,  Bangs, 1898:199. Type locality Point Romo, Anastasia Island, St. Johns County, Florida.
                        Peromyscus phasma, Bangs, 1898.
                        P. p. phasma, Osgood, 1909:107.
                         Endangered
                         Anastasia Island beach mouse

P. p. polionotus,  (Wagner), 1843:52. Type locality Georgia.
              Mus polionotus, Wagner 1843.
              Peromyscus subgriseus, Bangs, 1898:202, 215.
              P. polionotus, Osgood, 1907:49.

P. p. roadsi,  Bangs, 1898:201. Type locality Lutz, Hillsborough County, Florida.
              P. subgriseus rhoadsi, Bangs, 1898.
              P. p. rhoadsi, Osgood, 1909:107.

P. p. subgriseus,  (Chapman), 1893:341. Type locality Gainesville, Alachua County, Florida.
              Sitomys niveiventris subgriseus, Chapman, 1893.
              P. p. subgriseus, Schwartz, 1954:562.

P. p. sumneri,  Bowen, 1968:20. Type locality Merial Lake, Bay County, Florida.

P. p. trissyllepsis,  Bowen, 1968:17. Type locality E of Perdido Inlet, Baldwin
County, Alabama.
                      Endangered.
                       Perdido Key beach mouse
                       Two known locations (reintroductions)
 


             Alabama beach mouse                         Choctawhatchee beach mouse                      Santa Rosa beach mouse

REFERENCES
Bangs, O. (1898).  A new name for the Georgia old field mouse.  Science 8:
214-215

Blair, WF. (1942). Systematic relationships of Peromyscus and several related genera as shown by the baculum. Journal of Mammalogy. 23: 196-204.

Blair, W. F. (1951). Population structure, social behavior, and environmental relations in a natural population of the beach mouse (Peromyscus polionotus leucocephalus). Contributions of the Laboratory of Vertebrate Biology, University of Michigan 48: 1-47.

Bowen, W. W. (1968).  Variation and evolution of Gulf coast populations of beach mice, Peromyscus polionotus. Bulletin of the Florida State Museum 12: 1-91.

Bowen, W. W. and W. D. Dawson (1977). Genetic analysis of coat pattern variation in oldfield mice (Peromyscus polionotus) of western Florida. Journal of Mammalogy 58: 521-530.

Caldwell, L. D. and J. B. Gentry (1965).  Natality in Peromyscus polionotus populations. American Midland Naturalist 74: 168-175.

Carmon, J. L., R. G. Williams, et al. (1967).  Effects of temperature and radiation on litter size and growth in Peromyscus polionotus. Growth 31: 79-89

Davenport, L. B. (1964).  Structure of two Peromyscus polionotus populations in oldfield ecosystems at the AEC Savannah River Plant.  Journal of Mammalogy 45:95-113.

Foltz, D. W. (1981). Genetic evidence for long-term monogamy in a small rodent, Peromyscus polionotus. American Naturalist 117: 665-675.

Gentry, J. B. and E. P. Odum (1957). The effect of weather on the winter activity of old-field rodents.  Journal of Mammalogy 38: 72-77.

Gentry, J. B. and M. H. Smith (1968). Food habits and burrow associates of Peromyscus polionotus. Journal of Mammalogy 49: 562-565.

Hall, E. R. (1981). The Mammals of North America. New York, John Wiley and Sons.

Hayne, D. W. (1936). Burrowing habits of Peromyscus polionotus. Journal of
Mammalogy 17: 420-421.

Holler, N. R. (1992).  Perdido Key Beach Mouse, Peromyscus polionotus trissyllepsis, (Cricetidae: Rodentia). Rare and Endangered Biota of Florida. S. R. Humphrey (ed.). University Press of Florida.
1: 103-109

Howell, A. H. (1939). Descriptions of five new mammals from Florida.  Journal of
Mammalogy 20: 363-365.

Hsu, T. C. and F. E. Arrighi (1968).  Chromosomes of Peromyscus (Rodentia, Cricetidae) I. Evolutionary trends in 20 species.  Cytogenetics 7: 417-446.

Huestis, R. R. (1932).  Local differences in pelage characteristics of Peromyscus.
Journal of Mammalogy 13: 210-218.

Kaufman, D. W. (1974).  Adaptive coloration in Peromyscus polionotus: Experimental selection by owls.  Journal of Mammalogy 55: 271-283.

Lynn, W. J. (2000).  Social organization and burrow-site selection of the Alabama beach mouse (Peromyscus polionotus ammobates).  M. S. Thesis, Auburn University.

Margulis, S. W. (1997). Inbreeding-based bias in parental responsiveness to litters of oldfield mice. Behavioral Ecology and Sociobiology 41: 177-184.

Margulis, S. W. (1998). Relationships among parental inbreeding, parental behaviour and offspring viability in oldfield mice. Animal Behaviour 55: 427-438.

Moyers, J. E. (1996). Food habits of Gulf Coast subspecies of beach mice (Peromyscus polionotus spp.). M. S. Thesis, Auburn University.

Novak, J. A.  (1997).  Home range composition and habitat use of Choctawhatchee beach mice.  M. S. Thesis, Auburn University.

Osgood, W. H. (1907).  Some unrecognized and misapplied names of American mammals. Proceedings of the Biological Society of Washington 20: 43-52.

Osgood, W. H. (1909).  A revision of the mice of the American genus Peromyscus. North American Fauna 28: 1-28.

Schwartz, A. (1954).  Oldfield mice, Peromyscus polionotus, of South Carolina. Journal of Mammalogy 35: 561-569

Smith, M. H. (1966).  The evolutionary significance of certain behavioral, physiological, and morphological adaptations of the Old-field mouse, Peromyscus polionotus.  Ph.D. Dissertation, University of Florida.

Smith, M. H. (1968).  Dispersal of the old-field mouse, Peromyscus polionotus. Bulletin of the Georgia Academy of Science 26: 45-51.

Smith, M. H. (1971). Food as a limiting factor in the population ecology of Peromyscus polionotus (Wagner). Annual of Zoological Fennici 8: 109-112.

Sumner, F. B. and J. J. Karol (1929). Notes on the burrowing habits of Peromyscus polionotus. Journal of Mammalogy 10: 213-215.

Swilling, W. R. and M. C. Wooten (2002).  Subadult dispersal in a monogamous species, the Alabama beach mouse (Peromyscus polionotus ammobates).  Journal of Mammalogy 83:

Te, G. A. and W. D. Dawson (1971). Chromosomal polymorphism in Peromyscus polionotus. Cytogenetics 10: 225-234.

Wolfe, J. L. and C. T. Summerlin (1989).  The influence of lunar light on nocturnal activity of the old-field mouse. Animal Behaviour 37: 410-414.