Demographics and Movements of Chipmunks in a Fragmented Landscape
 

Lauren Rule¹ and Tom Nelson²

¹Wake Forest University, Winston-Salem, North Carolina. ²Eastern Illinois University, Charleston, Illinois.

Introduction

Forest fragmentation occurs when large forests are cut, resulting in reduced size and increased isolation of the remaining forest patches (Figure 1). Specifically, it involves a reduction in total forest habitat, a reduction in patch size, an increased edge-to-interior ratio and an increased distance between patches.  The effects of fragmentation on wildlife species may include a reduction in the availability of suitable habitat, a decrease in quantity and diversity of food, an increase in predation and parasitism and decreased genetic variability. These factors lead to increased risk of local extinction within patches and decreased probability of re-colonization following extinctions.  Fragmentation affects the ecology of species at the individual, population and community levels (Nupp & Swihart 1998). Chipmunks do not inhabit agricultural fields, but tree lines and fencerows can provide corridors for dispersal between forest patches (Figure 2) (Henderson et al. 1985). Studies designed to measure faunal diversity have shown that chipmunks are not present in small forest patches (Rosenblatt et al. 1999). Nupp & Swihart (1998) suggested that chipmunks might have higher predation rates in small forest patches.

Objectives

1. Describe the demographics of chipmunk populations in relatively small and large forest patches.
2. Estimate home range sizes and maximum distances traveled.
3. Investigate which landscape features serve as barriers to movement.
 

Methods

This study was conducted during a ten-week period from June-August 1999. Two forest patches (one large and one small) in central Illinois served as study areas. Chipmunks were live-trapped using Sherman traps. Each animal was classified by age and sex, weighed, measured, and marked with ear tags (Figure 4). Selected individuals were radio-collared.  Radio-tagged chipmunks were located daily using a directional antenna and receiver to measure home range size and maximum daily movements.  Three individuals were subsequently moved to new locations to investigate the effects of landscape barriers.

Results

Demographics: We trapped thirty-five individual chipmunks on two study sites and put radio-collars on six of these. Estimated densities were similar on each study area (8.1/ha vs 7.3/ha for small and large patches, respectively).  Adults comprised 62% of the population in the large patch but only 27% in the small patch. Sex ratios did not differ between patches (Figures 4 and 5).

Home Range & Movements:  Summer home range size averaged 1.1 ha for all six radio-collared chipmunks. Adult males tended to have much larger home ranges (mean = 2.0 ha) than adult females and juveniles (mean = 0.3 ha). However, mean home range size did not differ between individuals in the large versus small forest patches.  The mean maximum linear distance traveled by radio-collared chipmunks was 188 meters. Adults males moved over longer linear distances than adult females or juveniles. The maximum linear distance moved by any chipmunk was 390 meters.

Agricultural Fields as Barriers to Movement: Adult male chipmunks moved 100, 200 and 300 meters away from the edges of their home ranges returned home within hours of release if they could travel in forest or along forested corridors. However, an individual moved ~200 m across a cornfield that lacked any fencerow or forested corridor would not cross the field and established a new home range near the release site.

Conclusions

These preliminary data suggest that chipmunks may be vulnerable to forest fragmentation when woodlots are surrounded and isolated by row crops. Isolated woodlots smaller than 1-2 ha may be too small to sustain viable chipmunk populations.

Acknowledgements

This project was funded by the National Science Foundation and Eastern Illinois University through the Research Experiences for Undergraduates Program.