The Anastasia Island Beach Mouse (Peromyscus polionotus phasma) is a subspecies of the oldfield mouse of the southeastern United States. It occurs in the sand dunes of Florida and Alabama beaches.
The Anastasia Island Beach Mouse Manatee has been classified by the United States Fish and Wildlife Service as an endangered species due to the specificity of its habitat and the natural and human-induced destruction thereof.
Information & Facts:
The Anastasia Island beach mouse has an average body length of 13.85–14.28 cm (5.45–5.62 in) including tail. The coat tends to be a pale tan color with a white underbelly. Subtle white markings can be found across the face and muzzle. Their coloration, being substantially lighter than inland members of their species, is thought to be an adaptation to help them blend into their sandy habitats and avoid predators. Males and non-reproducing females average a weight of 12.5 g (0.44 oz) and pregnant females have an average weight of 20 g (0.71 oz)
The mouse occurs in the sandy dunes of Anastasia Island in Florida. Though the species once ranged from St. Johns River in northern Florida to Anastasia Island in St. Augustine, Florida, habitat destruction limited and eventually eliminated populations in the northern part of the state.
The mature, sparsely vegetated, scrubby dunes offer the best burrowing environment, as well as providing the mice with ample food sources. These dunes tend to occur between the high-tide line and the more densely vegetated dunes farther inland. Though sometimes found in the inland dunes, very little foraging takes place there. The mice use the heavy coastal grass cover there to provide protection and avoid detection from predators. Occasionally, beach mice make their homes in abandoned burrows of ghost crabs, but are also capable of creating their own.
The mice eat small insects and coastal plants such as beach grasses and sea oats. They gather seeds which have separated from the plant and blown to the ground. Every night, they leave their burrows to gather the sea oat seeds which have blown to the ground, then return them to their burrows for storage.
Due to the highly variable climate of coastal habitats, though, several seasonal plants can offer additional food sources throughout the year, such as the beach pea (Galactia spp.), coastal ground cherry (Physalis angustifolia), dixie sandmat (Euphorbia bombensis), tall jointweed (Polygonella gracilis), seaside pennywort (Hydrocotyle bonariensis), seacoast marshelder (Iva imbricata), and evening primrose (Oenothera humifusa).
Burrows tend to be constructed at the base of a clump of grass on the sloping side of a dune, and are occupied by either a monogamous, mating pair of mice or a female and her young. The entrance is a small hole, typically 1–2 inches in diameter, followed by a 3–4 foot tunnel of the same diameter. The tunnel leads to a main chamber, which typically has a second ‘escape tunnel’ leading out the back. The escape tunnel has no opening at the surface, but ends just below the sand’s surface.
If the mouse’s burrow is invaded or disturbed, the mouse will access the escape tunnel and push through the layer of sand at the end to the surface. These burrows are used for food storage, sleeping, and nesting, as well as a refuge from predators.
The species is monogamous. Females reach reproductive maturity at 6 weeks and can produce a litter of pups in as little as 20–23 days. The breeding season lasts from November to early January, but can continue throughout the year if climate and food sources are optimal. The average litter of pups is 4, but can range in size from 2-7.
Though the average lifespan is 9 months, mortality is high and most young survive around 4 months.
The indigenous predators include coastal dwellers such as snakes, skunks, raccoons, and the great blue heron. Some introduced species which pose a threat to the mouse are domestic cats and dogs, as well as foxes.