Seasonal Demography and Movements of Cottontail Rabbits on Isolated Playa Basins

Abstract

We examined spatial and temporal changes in population density, age structure, and individual movement distances of eastern cottontail rabbits (Sylvilagus floridanus) on 2 playa lake basins in the Texas Panhandle. We obtained 1,857 captures of 931 individual rabbits during 7,450 trap nights from February through November 1981. Population densities during prereproductive periods were 8.2 and 11.6 cottontails per ha on playa basins A and B, respectively. Subsequent changes in density were related to reproductive recruitment and to dispersal. Densities peaked at 28.4 and 26.9 cottontails per ha on playa basins A and B, respectively, during summer trapping periods. Adult :juvenile ratios declined coincident with the production of 7 litters. Distribution of captures within each playa basin and dispersal patterns were related to seasonal maturation and harvest of surrounding crops. A greater (P 2 times revealed that seasonal movement distances reflected the availability of habitats (i.e., crops) surrounding playa basins. J. WILDL. MANAGE. 54(3):403-409 Fragmentation and isolation of wildlife habitats by agricultural practices in the United States have dramatically reduced the abundance and diversity of native wildlife (Burger 1978). In fragmented habitat, native wildlife populations have been subdivided spatially and restricted to small areas of permanent cover such as fence rows and shelter belts (Swihart and Yahner 1982). These populations may be regulated as much by the availability, spatial arrangement, and interconnected nature of habitat as they are by fecundity and mortality rates (Fahrig and Merriam 1985). In regions of intensive agricultural activity, wildlife inhabiting small relic areas of native habitat may represent source populations (Pulliam 1988) where reproduction exceeds available cover, food resources, and breeding sites. Similarly, surrounding agricultural areas may constitute population sinks. Crops provide marginal habitat for a portion of the year, but are eliminated after harvest. Agricultural habitats might be expected to alter seasonal movements and dispersion of individuals, increase the potential productivity of source populations, and facilitate dispersal among isolated areas of permanent cover. The eastern cottontail rabbit inhabits earlymidsuccessional habitats over much of the continental United States, including all but the southwestern portion of Texas (Davis 1974). Previous studies of cottontail reproductive phenology (Chapman and Morgan 1973) and population dynamics (Bothma and Teer 1977) were done in southern and southeastern Texas and over much of the species' native range (see Chapman et al. 1982). However, relatively little work has been done on cottontails in finite and dispersed playa basin habitats that dominate most of the southern Great Plains. We present data on seasonal changes in cottontail demographic characteristics and movements for discrete populations inhabiting playa basins in the Texas Panhandle. Our objectives were to document seasonal variations in population densities, age structure, and breeding chronology. Further, analyses of cottontail movements and dispersion were examined relative to changing population age structure and the influences of adjacent agricultural activities. This work was funded by the Caesar Kleberg Foundation for Wildlife Conservation, The Noxious Brush and Weed Control Program at Texas Tech University, and through contract DEAC09-765R00819 between the U.S. Department of Energy and the University of Georgia's Institute of Ecology. This paper is Manuscript Number T-9-291, College of Agricultural Sciences, Texas Tech University. i'Present address: Department of Zoology, University of Georgia, Athens, GA 30602. 2 Present address: School of Forest Resources, University of Georgia, Athens, GA 30602.