Juvenile Dispersal of Franklin's Ground Squirrel (Spermophilus Franklinii) from a Prairie "Island"

Article excerpt

ABSTRACT.-

Franklin's ground squirrel (Spermophilus franklinii) is declining in the eastern portion of its range, and this decline is often attributed to habitat fragmentation. However, the ability of S. franklinii to disperse across an agricultural landscape is not known. During spring 2002 we live trapped a small, apparently isolated, population of Franklin's ground squirrels in a 12-ha tallgrass prairie restoration located south of Urbana, Champaign County, Illinois. This prairie "island" was surrounded primarily by row-crop agriculture. We radio-tracked 14 juvenile Franklin's ground squirrels (seven males and seven females) throughout dispersal to determine how far dispersers traveled, the timing of dispersal, if dispersal distance differed between sexes and if the agricultural matrix surrounding the study site was a barrier to movements. Males dispersed farther than females, but individuals of both sexes moved ≥1 km from the study site. The farthest movement recorded was by a male who traveled 3.6 km. Dispersal was age-dependent for both sexes, occurring at 9-11 wk of age. Agricultural fields did not seem to hinder movement, probably because dispersal occurred in late July and August before row crops were harvested. Open areas such as roadways, however, may be barriers for some individuals.

INTRODUCTION

Franklin's ground squirrel (Spermophilus franklinii) is declining in much of the Midwestern United States (Van Petten and Schramm, 1972; Lewis and Rongstad, 1992; Johnson and Ghoromanski-Norris, 1992; Pergams and Nyberg, 2001; Martin et al., 2003). The International Union for Conservation of Nature and Natural Resources (IUCN) lists this species as S2 (Imperiled) in Indiana, Kansas, Missouri and Wisconsin; and as S3 (Rare) in Iowa (Pergams and Nyberg, 2003). Spermophilus franklinii was listed as State Threatened in Illinois in 2004 (Illinois Endangered Species Protection Board, 2004). The decline of this grassland species parallels the loss of its favored habitat to agricultural practices and human encroachment (Van Petten and Schramm, 1972; Lewis and Rongstad, 1992). Conservation actions focused on S. franklinii likely would benefit other grassland dependent species as well, but the ecology of S. franklinii must be better understood before effective and efficient management actions can be taken (Martin et al., 2003).

Habitat descriptions for Spermophilus franklinii in the literature are general. Franklin's ground squirrels are associated with the thick vegetation of tallgrass and mid-grass prairies and are rarely seen in open areas (Haberman and Fleharty, 1972; Ellis, 1982; Jones et al., 1983; Hoffmeister, 1989; Benjamin, 1991; Kurta, 1995). In Illinois, prairie remnants and restorations lack the area, natural disturbance regimes and species composition of the historical prairies that S. franklinii once inhabited. Midwestern grasslands also typically occur in a highly fragmented state within an agriculturally dominated matrix. To persist in this landscape, S. franklinii must be able to utilize relatively small, sometimes isolated, patches of habitat and have the ability to move through the matrix to other patches. A common perception is that the decline of S. franklinii is related to habitat fragmentation (Martin et al., 2003), but no studies have examined the dispersal abilities of juvenile Franklin's ground squirrels in the agricultural Midwest. It is not clear how far individuals are able to disperse or if the structure of matrix habitat limits dispersal.

In this study, we radio-tracked 14 juvenile Franklin's ground squirrels throughout the dispersal process to examine the demography of dispersers, the timing of dispersal, how far animals will travel and if the agricultural matrix is a barrier to movement.

STUDY SITE

The Barnhart Grove Prairie is a 12-ha tallgrass prairie restoration located 3 km south of Urbana, Illinois, that is maintained by the Barnhart Grove Prairie Restoration Project, a not-for-profit corporation, in conjunction with the Champaign County Soil and Water Conservation District and the Illinois Department of Natural Resources. …