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ABSTRACT.-We live-trapped small mammals at 12 sites and compiled data from 3 previous live-trapping studies to document the distribution of the eastern chipmunk (Tamias striatus) in the Shawnee National Forest (SNF) in southern Illinois. Chipmunks were not captured at sites in large areas of the eastern SNF. We collected data on canopy composition and coarse woody debris (CWD) at 8 sites where chipmunks were absent and 5 sites where they were present. Canopy composition and CWD did not differ significantly between sites with and without chipmunks. We could not recognize any geographic barriers that would prevent dispersal into the eastern SNF by chipmunks. Thus, the absence of chipmunks in the eastern SNF seems inexplicable at this time.
INTRODUCTION
The eastern chipmunk (Tamias striatus) is a common and conspicuous inhabitant of brushy and forested habitats throughout most of the eastern United States and southeastern Canada (Hall, 1981). Eastern chipmunks are distributed throughout Illinois, but are missing from some areas where ecological conditions seem favorable (Hoffmeister, 1989). For example, Rosenblatt el al. (1999) did not capture eastern chipmunks in woodlots in agricultural areas of central Illinois, probably due to the isolation of these woodlots and the aversion of chipmunks for open habitats such as agricultural fields (Henderson et al., 1985; Bennett et al., 1994). Hoffmeister (1989) noted that eastern chipmunks also seem to be absent from the eastern Shawnee National Forest (SNF), but did not provide actual survey data to support this pattern or suggest hypotheses to explain it. Forested habitat in the eastern SNF is extensive and isolation or forest fragmentation cannot explain this anomaly in distribution. Eastern chipmunks avoid areas that flood or are cultivated (Hoffmeister, 1989) and require well-drained sites for burrows, particularly during hibernation. The eastern SNF includes many bluffs, steep ravines and upland forest habitats. However, that should provide suitable locations for burrows and hibernation sites. There are no obvious geographic barriers to limit dispersal of eastern chipmunks into the eastern SNF.
Bowers (1995) reported that the abundance of eastern chipmunks was positively associated with a closed canopy and open understory. However, the tree species composition of the forest canopy also may be important in determining habitat quality. For example, the availability of acorns in the fall and winter has a...