Reproduction in the Hispid Cotton Rat, 
Sigmodon hispidus Say and Ord (Rodentia: Muridae), 
in Southeastern Virginia 
Robert K. Rose and Michael H. Mitchell 
Department of Biological Sciences 
Old Dominion University 
Norfolk, Virginia 23529 
ABSTRACT . — The hispid cotton rat, Sigmodon hispidus Say and 
Ord, a species of the southwestern United States that has been moving 
northward and eastward in this century, was first observed in Virginia 
in 1940. In this study of the cotton rat in southeastern Virginia, most 
males were reproductively competent from February through November, 
embryos were recorded from March through October, and litter sizes 
were comparable to those from other locations except Kansas. Also 
unlike the cotton rat in Kansas, animals grew at substantial rates 
during the winter in Virginia. The hispid cotton rat seems to have 
adjusted its breeding season in Virginia by the cessation of breeding 
early in autumn, which permits the last young of the season to attain 
nearly adult size before winter arrives. Both young and adults are able 
to maintain and even increase their autumnal body mass throughout 
the winter. Timing and length of the breeding season and the patterns 
of body growth suggest that the hispid cotton rat is well adapted to 
winter, and hence to persistence of the species, in southeastern Virginia. 
The hispid cotton rat, Sigmodon hispidus Say and Ord, is a 
cricetine rodent that has dramatically expanded its distribution in the 
central and southeastern states in historic times (Genoways and Schlitter 
1967). First recorded in Virginia from Mecklenberg Co. in 1940 (Patton 
1941), it moved northward in the lower Piedmont into Amelia Co. 
(Lewis 1944) and then north of the James River in central Virginia 
(Pagels 1977). The current distribution is believed to extend from 
Virginia Beach westward to points north of Richmond and southwestward 
through Halifax Co., or approximately throughout the southeastern 
one-third of Virginia. 
Because the hispid cotton rat has tropical affinities (Hall 1981, 
Zimmerman 1970), it is surprising that the species has been able to 
extend its range to the present northern limit of its distribution and to 
cope with winters in such states as Kansas, Tennessee, and Virginia. 
Furthermore, we expected to observe that this rodent has a shorter 
breeding season in those marginal populations than in Texas or Mexico, 
which are closer to the center of distribution for the species. In fact, 
Brimleyana 16:43-59, July 1990 
43 
