The oldfield mouse or beach mouse is a nocturnal species of rodent in the family Cricetidae. It is found in the southeastern United States on sandy beaches, in corn and cotton fields, and in hedge rows and open timber tracts. Coloration varies with geographic location; inland populations are generally fawn-colored, while coastal populations are lighter or white. The mouse eats seeds, fruits, and occasionally insects, and lives and raises its three to four young in a simple burrow. Weaning occurs at 20–25 days, and females may mate at 30 daysof age. Predators are those that prey on small mammals. One individual lived in captivity for about five years. The mouse is of least concern to conservationists because it is abundant and widespread, and no major threats exist for the species as a whole, but several subspecies with small distributions are endangered or even extinct.
The oldfield mouse occurs only in the southeastern United States from central Alabama, south-central Tennessee, western South Carolina, northeastern Mississippi, and Georgia to the Gulf Coast and through western and most of peninsular Florida. The mice prefer sandy fields and beaches, but choose corn and cotton fields, and occasionally hedgerows and open timber tracts. Land and beachfront development threaten habitat. Populations of up to six per acre have been recorded.
Description
The mouse has fawn-colored upperparts and gray to white underparts through most of its range, but on white sandy beaches, the mouse is light or even white. Inland populations are darker and smaller with shorter tails that are dusky above and white below. General body and tail color may vary slightly depending upon geographical location.
Behavior
The mouse is primarily nocturnal.
Diet
P. polionotus is omnivores and the principal diet is seasonal seeds of wild grasses and forbs, but blackberries, acorns, and wild peas may be consumed. Insects consumed include beetles, leaf hoppers, true bugs, and ants. Vertebrates are consumed. Beach populations consume the fruits and wind-deposited seeds of sea oats and sea rocket, and feed on invertebrates when seeds are scarce.
Shelter
The beach mouse burrows and leaves mounds of earth around the burrow entrance. The burrow slopes down from the entrance for a space then levels off with a nest at its end. A branch of the burrow may extend above the nest to just a few centimeters below the surface as an emergency exit. Should the burrow be disturbed, the mouse "explodes" through the sand via the exit and dash off. The mouse closes any burrows in heavy rains should flood threaten. Spiders, snakes, and other species may move into a burrow.
Reproduction
The mice are monogamous. Gestation is 23–24 days, possibly 25–31 if the mother is still lactating from a previous litter. Mean litter size is three or four. When birth is imminent, the female assumes a crouching position and may rise to a more erect position as each young is born. She may aid the birth by gently pulling on the young with her fore feet, as one mouse has been observed doing. The placenta may be removed in the same manner. She then eats it. The umbilical cord is broken by pulling or chewing or when the placenta is consumed. She may stretch and groom between deliveries. Births usually occur in the daytime and usually over several minutes or even an hour. The pinkish newborn may be washed by the mother following the last delivery and weigh between. The pinnae elevate in 3–5 days, the lower incisors erupt in 6–7 days, and the eyes open in 10–16 days. Weaning is gradual and occurs over 20–25 days. First estrus may occur as early as one month and first litter at 53 days of age. The juvenile pelage is gray. At one week, the young weigh, at three weeks, and at five weeks. The young in one study dispersed before establishing their homes.
Survival
Presumed predators are those that prey upon small mammals including house cats. Parasites found in mice from Florida were six species of nematodes, one each of trematodes and acanthocephalans, and two of fleas. One mouse survived in captivity 5.5 years.
Conservation
The IUCN lists the species as of least concern because it is widespread and abundant, and no major threats to the species exist at this time. It is found in many protected areas. Of the 16 subspecies, eight coastal forms are of conservation concern. All eight subspecies have restricted distributions and are threatened by habitat loss and associated pressures due to tourism and land development.
