132 
John B. Andre 
Differences in abundance of small mammals among habitats were 
compared by Chi-square test. Equal probability of capture in each habi- 
tat was assumed. For each species, expected frequency (E) in each habitat 
was calculated by dividing the number of trap nights executed in habitat 
A by the total number of trap nights executed in habitats A and B, then 
multiplying by the number of individuals captured in habitats A and B. 
RESULTS AND DISCUSSION 
Trapping results, habitat use, and relative abundance of the four spe- 
cies of small mammals found on Bulls Island are shown in Table 1. The 
percent trapping success for each species in each habitat is the relative 
abundance value (RAV). Comparisons of the RAVs of different species 
within a habitat, and of the same species among habitats, reflects the 
degree of a species’ use of a habitat. 
The rice rat, Oryzomys palustris, was the only species captured in the 
sand dune, freshwater marsh, and salt spray forest habitats. It was 
equally abundant in the freshwater marsh (2.9 RAV) and salt spray forest 
(2.7 RAV) habitats, and less abundant in the sand dunes (1.6 RAV). The 
differences were not significant(X^=2.22, 1 df, p>0. 10). The freshwater 
marsh and salt spray forest habitats are structurally complex, with 
patches of grass and dense, tangled stands of small trees and shrubs. By 
contrast, the vegetation of the sand dunes was sparse and structurally 
simple with only scattered, dense stands of sea oats. Oryzomys prefers 
habitats with a dense cover of grasses or sedges (Golley 1962). On Bulls 
Island vegetation of this type was found only in small patches in the 
dunes, providing little habitat for Oryzomys, 
The maritime live oak forest produced the fewest mammals of all 
habitats despite the greater number of trap nights. Oryzomys and the 
cotton mouse, Peromyscus gossypinus, yielded RAVs of 0.5 and 0.3, 
respectively. The maritime live oak forest of Kiawah Island was also 
sparsely inhabited by small mammals, presumably because the forest 
canopy reduces light penetration to the forest floor, reducing productiv- 
ity and resulting in little food and cover (Pelton 1975). The three Oryzo- 
mys I captured in the live oak forest were subadults, as judged by body 
size. Grant (1971) reported that subadult Microtus pennsylvanicus were 
more likely to inhabit suboptimal habitat than were adults. A more 
detailed study is needed to determine whether the same is true of Oryzo- 
mys on Bulls Island. 
Trapping in the salt marsh produced 36 O. palustris and 1 hispid 
cotton rat, Sigmodon hispidus. Oryzomys was significantly more -abun- 
dant there (9.4 RAV) than in any other habitat during winter (X^= 17.48, 1 
