Population Dynamics of the Cotton Rat in Southeastern Virginia

Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529-0266 (HGS: 15 Fillmore Avenue, Danbury, CT 06811) *Corresponding author: brose@odu.edu ABSTRACT We used monthly live trapping for 2.5 years to evaluate the life-history features of the most common small mammal, Sigmodon hispidus (hispid cotton rat), in an old field at its northern limit of distribution on the Atlantic Coast. Peak densities, achieved in late autumn or early winter, were among the highest recorded for the species and were more typical of geographically marginal populations rather than of central ones. Unlike some other marginal populations, hispid cotton rats in southeastern Virginia did not lose significant body mass over the winter (when few juveniles were present) and survival in winter was not significantly different from that of other seasons, perhaps due to the moderating effects on winter temperatures of the nearby Atlantic Ocean and Chesapeake Bay. Our study provides support for the presence of spring and autumn cohorts, with long-lived animals being drawn almost entirely from the latter. INTRODUCTION Sigmodon hispidus Say and Ord (hispid cotton rat), a 100-g herbivorous rodent, is the sole member of a tropical genus broadly distributed across the southern US, for which the northward expansion of its distributional range into the central states and along the