Distribution, Abundance, and Habitat of the Florida Grasshopper Sparrow

Abstract

In the early 1900's, the population of Florida grasshopper sparrows (Ammodramus savannarum floridanus) was reportedly large and widespread in Florida; however, surveys between 1980 and 1982 revealed only 93 sparrows at seven sites. The sparrow was found at only one of its former locations, suggesting a reduction in both abundance and occupied range. Although the subspecies prefers stunted oaks (Quercus sp.) and saw palmettos (Serenoa sp.), its ecological requirements seem liberal enough to enable it to persist in some managed cattle pastures. Compared with the habitat of the eastern grasshopper sparrow (A. s. pratensis), habitat used by floridanus has lower values for variables pertaining to vegetation height, vertical density, litter depth, and litter cover, but much higher values for percentage shrub cover and bare ground. Habitat loss or alteration due to pasture management is the greatest threat to the subspecies. A low growth of palmettos and woody shrubs should be maintained in areas where the sparrow occurs. Federal listing of the Florida grasshopper sparrow as threatened or endangered may be appropriate due to its probable low numbers, restricted distribution, and loss of habitat. J. WILDL. MANAGE. 49(3):626-631 The grasshopper sparrow occurs throughout most of temperate North America, but is confined to low to medium height grassland plant communities (Smith 1963). The Florida subspecies is geographically isolated from the eastern race by at least 500 km (Am. Ornithol. Union 1982) and appears to be limited in distribution to the prairie region of south-central Florida. The lack of distributional information precludes a precise delineation of the historical range, and early accounts provide no documented records of abundance. Although specific habitat requirements for floridanus are not known, preliminary investigations suggest they are atypical of the species (Howell 1932, Nicholson 1936). Because of an apparent population decline, the Florida grasshopper sparrow was classified as endangered by the State of Florida (Kale 1978). Much of the native prairie habitat has been converted to improved pasture (Davis 1980), which may have caused the extirpation of the subspecies from some of its former range. Recent observations, however, indicate th' the subspecies may be adapting to some managed pastures (Stevenson 1978). Surveys of the known range of the Florida grasshopper sparrow and potential habitat outside that range were conducted during the breeding season (Apr-Jul) from 1980-82 to gather information on its present distribution and abundance. Vegetation variables were measured at territories of male grasshopper sparrows to provide a quantitative description of habitat for possible use in management of the subspecies. This research was supported by the Fed. Aid to Endangered Species Program, Fla. Endangered Species Proj. E-1. R. L. Barker and S. A. Martin participated in the survey and assisted in locating survey areas. R. P. Wunderlin assisted with plant identification. C. L. Abercrombie provided statistical advice. J. Bart, T. C. Hines, D. S. Maehr, and L. E. Williams, Jr., reviewed earlier drafts of this manuscript and provided many useful suggestions. Special appreciation is extended to A. L. Adams, III, P. Clemons, D. W. Delargey, W. C. Funk, C. E. Lough, and P. T. Wilson, who provided access to their properties. STUDY AREAS AND METHODS Surveys were conducted in the dry prairie region of south-central Florida. Most of this habitat is located within the Kissimmee River Basin and west of Lake Okeechobee in parts of Glades, Hendry, Charlotte and Desoto counties (Davis 1980). In Florida, dry prairie grasslands are extensive treeless plains that often separate freshwater marshes and forested uplands. Seldom flooded, these grasslands are maintained in early successional stages by frequent fires. The vegetation is dominated by pineland threeawn