This small mouse forages mostly on seeds and fruits of dune plants
and occupies multiple burrows in the sands of a 15-mile island on
the Gulf coast.
Peromyscus polionotus tryssyllepsis
The beach mouse is brown along the back and white underneath with
large ears and dark eyes. Average weight is approximately 12.5
grams (0.45 ounces); average length, including the tail, is
approximately 10 centimeters (4 inches).
Beach mice are monogamous and usually mate for life.
Reproduction peaks in the winter but continues year-round if food
is available. Gestation is approximately 23 days, and females have
an average of four pups per litter. In the wild, mice
typically live from nine months to one year.
The subspecies occurs only on the 24-kilometer-long (approximately
15-mile) barrier island of Perdido Key, primarily at three sites:
Perdido Key State Park and the Perdido Key Unit of Gulf Islands
National Seashore, both in Escambia County near Pensacola, Florida;
and Florida Point in Gulf State Park, east of Gulf Shores,
Beach mice occupy the narrow dune ecosystem across the island.
They depend completely on dunes found only in scrub and coastal
strand habitat, particularly dunes with open sand and sparse
vegetation. Home range size varies among subspecies and
individual mice, but averages about 0.5 hectares (approximately
1.25 acres). Individual home ranges can overlap. The mice are
nocturnal, so they forage at night and spend the daytime in their
burrows. Within their home range, beach mice often maintain 20 or
more burrows where they sleep, nest, feed, and store seeds.
Beach mice primarily feed on the fruits and seeds of dune plants
such as sea oats, sea rocket, and bluestem. They occasionally eat
Endangered, added to the list in 1985.
Habitat loss and fragmentation associated with residential and
commercial real estate development constitute the primary threats
to this species. Additional threats include tropical storms and
hurricanes as well as predators, especially house cats.