Key Largo cotton mice are omnivorous and feed on a wide variety of plant and animal materials. Over 70 percent of the tropical hardwood hammock trees and shrubs produce fruits and berries that may provide important food items for the Key Largo cotton mouse (USFWS 2008 and references therein).
The Key Largo cotton mouse is closely associated with the Key Largo woodrat (Neotoma floridana smalli). It is often found in woodrat holes, nests, or runways (Humphrey 1992, cited in USFWS 1999). Both of these species are dependent upon the
structure, composition, and quality of tropical hardwood hammocks. Several species listed by the USFWS as threatened or endangered occur in the same habitat or adjacent habitat, including the American crocodile (Crocodylus acutus), eastern indigo snake (Drymarchon corais couperi), and Schaus swallowtail butterfly (Papilio aristodemus ponceanus). In addition, there are at least seven state-protected animals and 20 state-listed plants that also share the same habitat, such as the threatened white-crowned pigeon (Columba leucocephala) and Miami black-headed snake (Tantilla oolitica) and the endangered lignumvitae tree (Guaiacum sanctum), prickly apple (Harrisia simpsonii), tamarindillo (Acacia choriophylla), powdery catopsis (Catopsis berteroniana), and long strap fern (Campyloneurum phyllitidus) (USFWS 1999).
Some of the behavioral and ecological information available for the Key Largo cotton mouse is inferred from other cotton mouse populations in Florida. The Key Largo cotton mouse builds leaf-lined nests in logs, tree hollows, and rock crevices. The holes occupied by these mice measure 3 to 9 cm in diameter, are often partially covered by leaves or bark, and may be located at the bases of trees and near or in woodrat nests. The Key Largo cotton mouse can move at least 2 km in 1 to 2 days. Male cotton mice have larger home ranges than females and home ranges overlap because cotton mice do not defend territories. Other Florida populations of cotton mice are primarily nocturnal and often run and climb on tree limbs and Key Largo cotton mice probably share these behaviors. Cotton mice use a variety of short musical barking sounds to communicate, which is probably also true for the Key Largo cotton mouse (USFWS 1999 and references therein).
Cotton mice are among the most common small mammals in South Florida and throughout the southeastern United States, but the Key Largo cotton mouse is endemic to (i.e., found only in) Key Largo. Although at one time it occurred throughout the tropical hardwood hammocks in the Upper Keys south to near Tavernier, today the Key Largo cotton mouse is restricted to the northernmost portion of Key Largo. Urbanization of Key Largo has decimated the tropical hardwood hammock forests and has reduced the availability of food, shelter, and habitat for the Key Largo cotton mouse, threatening its continued existence (USFWS 1999).
Data from 2007 suggest a stable population, but a rigorous monitoring program is only now being established. Conservation history, status, and plans for the future were reviewed by the U.S. Fish & Wildlife Service in 2008 (USFWS 2008).
The Key Largo cotton mouse formerly occurred throughout the tropical hardwood hammock forests of Key Largo, Monroe County, Florida, but is now restricted to the northern portion of Key Largo. Remaining hammocks on south Key Largo are small, isolated, and disturbed. Hammock fragments up to four hectares in size remain on south Key Largo, but may be too small and isolated to support viable cotton mouse populations (USFWS 1999).
A translocation project was initiated on Lignumvitae Key (outside the historic range of the Key Largo cotton mouse) in 1970, during which 14 individuals were released. A single individual was documented on the Key in 1977, but the population was considered extirpated by 1990 and a trapping survey in 2007 yielded no additional captures (USFWS 2008 and references therein).
The Key Largo cotton mouse uses a variety of tropical hardwood habitats, including recently burned, early successional, and mature hammock forests, and Salicornia coastal strand (the beach community just above the high tide line) adjacent to these forests (Humphrey 1992, cited in USFWS 1999). Much of the original tropical hardwood hammock on Key Largo was cleared in the past for development or agriculture. The southern portion of Key Largo is nearly completely developed, and the only remaining large contiguous tract of tropical hardwood hammock occurs on the northern half of the Key (USFWS 2008). Although a 1979 field study by Barbour and Humphrey (1982) found that a mature forest site had nearly twenty times the density of Key Largo cotton mice as did an intermediate-stage forest, more recent studies have suggested at least a somewhat greater degree of habitat flexibility (USFWS 2008 and references therein).
About a thousand hectares of tropical hardwood hammock remain in north Key Largo, mainly within the boundaries of Crocodile Lake National Wildlife Refuge and Dagny Johnson Key Largo Hammock Botanical State Park, which were acquired in 1980 and 1982, respectively (USFWS 2008). Both of these sites have been managed to maintain and restore the native tropical hardwood hammock vegetation on which the Key Largo cotton mouse depends and acquisition of the little additional remaining hammock habitat on north Key Largo has continued. Many tracts on these sites were cleared for development or agriculture during the 20th century, but hammock vegetation has returned to many of these previously cleared sites. The remaining forest is now composed of a variety of successional stages of tropical hardwood hammock vegetation, reflecting the time since and extent of disturbance (USFWS 2008).
The Key Largo Cotton Mouse is listed as endangered by both the U.S. Fish & Wildlife Service (USFWS) and the Florida Fish and Wildlife Conservation Commission (FWC) (USFWS 2008). The USFWS first listed this species in 1983 (Federal Register, 48 FR 43040-43043).
Cotton mice are short-lived, with an average life expectancy of perhaps just 5 months, although potential longevity is 2 to 3 years (USFWS 1999).
Key Largo cotton mice are larger and more reddish in appearance than other subspecies of cotton mice from peninsular Florida.The coat is reddish dorsally (above), with dusky brown sides, sharply contrasting white underparts, and a cinnamon buff wash on the throat and chest. The feet are white with dusky ankles. The bicolored tail is darker brown on top and whiter underneath. Body length is 170 to 189 mm, tail length is 72 to 87 mm, and hind foot length is 21 to 23 mm (Schwartz 1952).
In a 1979 trapping survey on Key Largo, population density was estimated at 21.8 individuals per hectare in a mature forest site and just 1.2 individuals per hectare in an intermediate-stage forest site (Barbour and Humphrey 1982).
In a later study, Humphrey (1988) found that density estimates varied considerably among sites, but averaged 15.5 individuals per hectare in three sites near housing subdivisions and 26.9 in three sites distant from such developments, yielding an overall average density for the study of 21.2 cotton mice per hectare. Using an estimate of 851 hectares of remaining forest habitat on north Key Largo at the time, Humphrey estimated the total Key Largo cotton mouse population at about 18,000 individuals.
The Key Largo cotton mouse breeds throughout the year. producing two to three litters annually, with an
average of four young per litter (Brown 1978, cited in USFWS 2008).
Peromyscus gossypinus allapaticola has been recognized as a valid subspecies since it was first described in 1952 (USFWS 2008) and is distinguished mainly by its overall larger size and brighter, reddish-colored fur. Its name is derived from the Seminole word "allapattah", which refers to the tropical dry hammocks of South Florida where this mouse is most abundant (Schwartz 1952).
The main threats currently facing the Key Largo cotton mouse are population fragmentation (as a result of habitat fragmentation), small total population size (2007 estimate: 17,000 individuals), and predation. Habitat degradation and loss have continued and threats from non-native animals and invasive exotic plants have increased, although efforts are underway to manage these threats (USFWS 2008).
The Key Largo cotton mouse has a number of natural predators, including raptors (birds of prey), corn snakes (Elaphe guttata), diamondback rattlesnakes (Crotalus adamanteus), Florida black racers (Coluber constrictor priapus), Keys rat snakes (Elaphe
obsolete deckerti), owls, and possibly raccoons (Procyon lotor). Non-native predators include free-roaming domestic cats (Felis catus), fire ants, and possibly young Burmese pythons (Python molurus bivitattus). Predation would probably not be a major concern if Key Largo cotton mouse population levels were robust and plenty of suitable habitat were available. However, in the face of habitat and population fragmentation, predation pressure can have a substantial negative impact (USFWS 2008).
In studying the spatial distribution of Key Largo cotton mice, Keith and Gaines (2002, cited in USFWS 2008) detected a relationship between the presence of the mice and the absence of invasive exotic plants.
