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ABSTRACT.-We document the first known occurrences of the cotton mouse (Peromyscus gossypinus) in Illinois since 1909. Mean hind foot length and body mass of cotton mice from study areas in two counties were significantly greater than sympatric white-footed mice (P. leucopus). The cotton mice occurred in forested bottomland habitat.
INTRODUCTION
The cotton mouse (Peromyscus gossypinus) is fairly common throughout most of its range from Virginia to Florida, W to eastern Texas and N through Tennessee to western Kentucky. The species reaches the northwestern periphery of its range in the Midwest in extreme southern Illinois. Historically, limited numbers of P. gossypinus were reported from five counties in Illinois: Alexander, Johnson, Pope, Pulaski and Union (Hoffmeister, 1989). However, none have been documented in Illinois since 1909. As noted by Hoffmeister (1989:215), "What has happened to P gossypinus in southern Illinois remains a mystery. Ample search within the last 30 years has been made specifically for these mice. Trapping has been done in habitat that should be suitable for the species but no specimens of P. gossypinus have been found."
Cotton mice occur in a variety of habitats, but in general are associated with bottomland forests and swampy areas (Wolfe and Linzey, 1977). Identification of cotton mice can be problematic because of their morphological similarity to other species of Peromyscus, including the white-footed mouse (P leucopus) (Linzey et aL, 1976; Engstrom et al., 1982; McDaniel et al., 1983). Here we report captures of cotton mice in Illinois for the first time since 1909.
METHODS
Small mammals were livetrapped in July, August and September, 1996, as part of a larger investigation on 27 sites throughout the Horseshoe Lake Conservation Area (HLCA), Alexander County, Illinois. Located in the Mississippi River floodplain, HLCA encompasses 3702 ha. Horseshoe Lake is a shallow, eutrophic, oxbow lake surrounded by emergent wetlands, and swamps dominated by bald cypress ( Taxodium distichum) and tupelo (Nyssa aquatica). Mesic and bottomland forest areas of HLCA include a variety of overstory trees, including pin oak (Quercus palustris), red maple (Acer rubrum), sweet gum (Liquidambar styraciflua), hackberry (Celtis occidentalis), cottonwood (Populus deltoides), box elder (A. negundo) and willow (Salix nigra). Understory on most sites is very sparse and often includes poison ivy (Toxicodendron radicans), greenbriar (Smilax sp.) and grape...