The oldfield mouse, oldfield deermouse or beach mouse (Peromyscus polionotus) is a nocturnal species of rodent in the family Cricetidae. It is a species of the genus Peromyscus, a closely related group of New World mice often called "deermice", that primarily eats seeds. It lives in holes throughout the Southeastern United States in beaches and sandy fields. Predators to these mice include birds and mammals. In 2016, these mice were in the least concern category on the IUCN Red List with certain subspecies classified as extinct, critically endangered, endangered or near threatened.
Distribution and habitat The oldfield mouse occurs only in the southeastern United States, ranging from Florida to Tennessee. They primarily live in beaches and sandy fields.Whitaker 1998, p. 308
Description The mouse has fawn-colored upperparts and grey to white underparts through most of its range, but on white sandy beaches, the mouse is light or even white to help them stay hidden from predators. 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. Measurements (20 adults from Alabama, Florida, and Georgia)StatisticAverageRangeLengthTailHind foot Weight Diploid number48Tooth formula = 16
Behavior The mouse is primarily nocturnal. Oldfield mice construct elaborate burrow systems with entrance tunnels, nest chambers, and escape routes.
Diet P. polionotus is omnivorous and the principal diet is seasonal seeds of wild grasses and forbs, but blackberries, acorns, wild peas, and arthropods may be consumed.Whitaker 1998, p. 309Wooten
Shelter These mice dig holes in earth to create homes. Spiders, snakes, and other animals may move into a burrow.Whitaker 1998, p. 308–9
Reproduction The mice are monogamous. When they are born, the baby mice are vulnerable, hairless, and blind. ReproductionWhitaker 1998, p. 309–10Sexual maturity (female)30 daysGestation23–24 daysLitter size3–4 (viviparous)Weight at birthWeaning20–25 days Adult weight
Survival Birds and mammals prey upon the oldfield mouse. Various types of parasites can effect oldfield mice, with nematodes being the main ones.Whitaker 1998, p. 310 The average lifespan of a mouse in the wild is 18 months, though one mouse survived in captivity for 5.5 years.Peromyscus polionotus They are primarily nocturnal to avoid predation.
Conservation In 2010, the beach mouse was in the least concern category on the IUCN Red List. For the beach mouse's subspecies, out of sixteen known, one is extinct, one was listed critically endangered, four endangered and two near threatened.
Under the Endangered Species Act of 1973, the following beach mice are protected as endangered or threatened subspecies: Southeastern beach mouse (P. p. niveiventris) – Threatened Anastasia Island beach mouse (P. p. phasma) – Endangered Alabama beach mouse (P. p. ammobates) – Endangered Perdido Key beach mouse (P. p. trissyllepsis) – Endangered Choctawhatchee beach mouse (P. p. allophrys) – Endangered St. Andrew beach mouse (P. p. peninsularis) – Endangered
The pallid beach mouse (P. p. decoloratus) is presumed extinct. The Santa Rosa beach mouse (P. p. leucocephalus) is listed as critically imperiled by NatureServe.
Predation In Florida, beach mice may be eaten by some growth stage of invasive snakes such as Burmese pythons, reticulated pythons, Southern African rock pythons, Central African rock pythons, boa constrictors, yellow anacondas, Bolivian anacondas, dark-spotted anacondas, and green anacondas.
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