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Perdido Key Beach Mouse

Alexandra Colombara, Auburn University
The Perdido Key beach mouse (Peromyscus polionotus trissyllepsis), is a subspecies of the Oldfield mouse (Peromyscus polionotus). This small rodent was first recognized in Alabama in 1968 as one of eight coastal subspecies. Its name is based on latinized versions of the Greek perone, meaning "pointed," myskos meaning "mouse," polios meaning "gray," and otos, or "ear," with the subspecies name meaning "triple" from trissos and catching from lepsis. Extensive beachfront development, habitat destruction, and predation by domestic cats all threaten this unique animal with extinction, and it was listed as an endangered species in 1985 by the federal government.
Historically, the Perdido Key beach mouse ranged from Perdido Key Island, Alabama, to Pensacola Bay, Florida. The Perdido Key beach mouse was first described in 1909 by William H. Osgood, an American zoologist who believed it to be a subspecies of the Oldfield mouse, known as Peromyscus polionotus albifrons. In 1968, however, Wilfred Wedgewood Bowen, an American zoologist and ornithologist, conducted a taxonomic study in which he discovered five previously unknown subspecies of the Oldfield mouse. Bowen chose the subspecies name trissyllepsis ("tri" meaning triple or three) based on his belief that the subspecies evolved from the genetic mixing of three other beach mouse species: griseobracatus, ammobates, and teucocephalus.
The Perdido Key beach mouse is a small rodent with average body length ranging from 4.5 to 5.5 inches (115 to 140 millimeters); it typically weighs around a half an ounce (10 to 15 grams). The adult female mice are slightly larger than males. The fur, called pelage, is distinctive. The belly, feet, and head are white, and the tail is white to greyish-brown. The back ranges from grey to fawn to wood brown, depending on the dominant coloration of the mouse's sand-dune habitat. The Perdido Key subspecies is distinguished from other subspecies by its much paler fur and variation in pelage patterns. The mice form monogamous pairs, meaning that only one male and one female live and breed together. The mice become sexually mature at approximately one month old and can breed year-round but are most active from November through January. Females typically have three or four offspring in a single litter and can produce two or more litters of young per year.
The mice live in the sandy dune environments of Alabama's Gulf Coast, where conditions are very dry and plant life is scarce. They construct burrows about three feet (approximately one meter) below the sand surface in a very particular pattern, with each burrow having an entrance tunnel, a main nest chamber, and an escape tunnel to use in case of a predator attack. Burrows can be identified among dunes by a mound of sand marking the entrance to the main tunnel. Perdido Key beach mouse burrows play an important role in the coastal ecosystem. They provide habitat for many other species, such as gopher frogs, camel crickets, and both black widow and Carolina wolf spiders. The mice are also essential to the survival of native plants by dispersing seeds through their feces and allowing uneaten seeds to grow in dune habitats. Although vegetation is sparse in the harsh dune environment, the mice feed on available plants such as sea oats and bluestem, as well as a variety of insects. They store food in underground hoards for times of scarcity. The mice are subject to intense predation from owls, skunks, foxes, raccoons, snakes, and more recently introduced domestic cats. Their main defense from these predators is their fur color, which allows them to blend into their surroundings.
The Perdido Key beach mouse today is limited to an area of only 60-155 square miles (100-250 square kilometers) in the coastal sand dune regions of Baldwin County, Alabama, and Escambia County, Florida. The Perdido Key beach mouse is a federally protected subspecies and was listed as endangered in the U.S. Endangered Species Act in 1985. The mouse is also listed as critically imperiled by the Alabama Natural Heritage Program, based at Auburn University. Human encroachment on Alabama's coast has been the primary cause, placing extreme pressures on the Perdido Key beach mouse habitat. The mice live on valuable beachfront property, and as more and more development occurs, their territory becomes smaller and more fragmented. The Perdido Key area has experienced enormous population growth over the last century, and the beach mouse has lost valuable habitat to houses, hotels, and shopping complexes. Additionally, studies on the few remaining populations of beach mice found that they face imminent extinction because of heavy predation by cats. In addition to human-caused population pressures, storms can be devastating to the mice. In the past, when numbers were high, mice from neighboring populations were able to recolonize areas after destructive hurricanes wiped out dune populations. Today, however, there are not enough mice to re-establish populations after existing ones are killed by storms. Many reintroduction efforts have failed because major hurricanes killed off newly transplanted mice.
In 1987, the U.S. Fish and Wildlife Service developed a recovery plan for this subspecies that outlines three main goals: maintenance and restoration of suitable habitat, development of reestablishment programs, and education of the general public regarding beach mice and their requirements for protection. Reintroduction programs have allowed populations to grow and survive natural disturbances such as hurricanes, and the mice have slowly increased in number and distribution during the last ten years of population monitoring. At the present time, the only remaining populations are found at Alabama's Gulf State Park, Florida's Perdido Key State Park, and Florida's Gulf Islands National Seashore.

Additional Resources

Bowen, W. Wedgwood. "Variation and Evolution of Gulf Coast Populations of Beach Mice, Peromyscus polionotus." Bulletin of the Florida State Museum of Natural History 12, no. 1 (1968): 1-91.
Holler, Nicholas R. "Perdido Key Beach Mouse Peromyscus polionotus trissyllepsis." In Rare and Endangered Biota of Florida. Vol. 1, Mammals, edited by Stephen R. Humphrey, 102-9. Gainesville: University Presses of Florida, 1992.
Published:  August 1, 2016   |   Last updated:  August 1, 2016