Use of Forest Fragments by Southern Flying Squirrels

Charlotte Higgins¹ and Tom Nelson²

¹Hastings College, Hastings, Nebraska. ²Eastern Illinois University, Charleston, Illinois.

Introduction

Southern flying squirrels are forest-obligate mammals that are widely distributed throughout Illinois and the eastern U.S. Preliminary studies suggest that these animals can move over large areas in contiguous forests, but rarely move across open areas. Consequently, forest fragmentation (the increased isolation and decreased size of forest patches) caused by agriculture may threaten the persistence of this species in the Midwest by isolating populations in small woodlots with little opportunity for dispersal (Figure 1).

Potential effects of fragmentation on species include:
1. Decreased population size,
2. Increased vulnerability to demographic and environmental variation,
3. Decreased genetic variability, and
4. Increased predation and parasitism.

Objectives

The threats posed to flying squirrels by fragmentation are poorly understood because we know little of their home range and habitat requirements. The objectives of this study were to:
1. Investigate the presence or absence of squirrels in large, medium and small forest patches,
2. Estimate home range size during summer, and
3. Characterize cavity trees utilized as daytime roosts.
 

Methods

We surveyed the presence or absence of flying squirrels in eleven forest patches using nest boxes  and Sherman traps. Four adult squirrels were radio-collared (Figure 2) and tracked during four weeks in July, 1999. Trees used as daytime roosts by these individuals were compared to randomly-selected trees at each site.

Results

	Less than 1% of forests in Central Illinois are more than 50 ha in size.
	Den trees were significantly taller than random trees.
	Squirrels selected larger diameter trees.
	Table 1.  Minimum patch size selected by flying squirrels.
	Table 2. Summer home ranges of flying squirrels.

Minimum Patch Size: We found flying squirrels in only two of eleven forest patches and both of these patches were more than 100 ha in size (Table 1).

Summer Range: Conservative estimates of summer home range suggest that individual squirrels need at least 2 ha of suitable summer habitat. Prior studies have suggested that they use 5-6 ha during a year (Table 2).

Conclusions

1. Flying squirrels appear to be area-sensitive and may be impacted by forest fragmentation.
2. Individuals require summer home ranges of at least 2-5 ha.
3. Tall, large diameter trees are preferred roosts

Acknowledgements

This study was funded by the National Science Foundation’s Research Experiences for Undergraduates Program and Eastern Illinois University.