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Movements and Habitat use of Franklin's
Ground Squirrels in Duck-Nesting Habitat

Discussion


Some movement patterns of Franklin's ground squirrels that we described using radio telemetry differed from patterns determined by others using capture-recapture data. In our study, squirrel activity was relatively constant throughout the day, whereas Haberman and Fleharty (1971) and Haggerty (1968) suggested bimodal patterns. Our estimates of home-range size are much larger than earlier estimates of 0.24-3.79 ha for males and 0.08-2.36 ha for females (Haggerty 1968, Krohne et al. 1973). Biweekly home-range sizes of females were largest during the post-lactation period in contrast to Haggerty (1968) who reported female home ranges decreased after young appeared above ground. We believe our telemetry data more accurately describe movements of the species.

Changes in biweekly geometric centers of activity may relate to use of patchily distributed foods. Daily home ranges of antelope ground squirrels (Ammospermophilus nelsoni) were much smaller than annual home-range sizes and were related to the distribution of seasonal food sources (Bradley 1967). Roundtail ground squirrels (Spermophilus tereticaudus) may periodically shift home-range location to include seasonal food resources (Drabek 1973). Although vegetative material (including seeds and fruits) typically makes up ≥66% of the diet of Franklin's ground squirrels, insects, small mammals, and bird eggs are also consumed (Bailey 1926, Lyon 1932, Sowles 1948, Haggerty 1968). An abundance of foods produced by shrubs and trees in TB and the availability of waste sunflower seeds in the adjacent cropland may explain, in part, the disproportionate use of this habitat by ground squirrels. The movement patterns of the ground squirrels appear well-adapted to exploit periodic concentrations of foods.

Ground squirrel use of upland habitat blocks on the WPA did not correspond to their relative availability. The pattern of use among the habitat blocks could not be explained by differences in vegetation height and density or litter depth. Because no clear pattern to the difference in vegetative structure among these habitats was evident, we hypothesize that unknown characteristics relating to the presence of pocket gopher burrow systems had a major, but indirect, influence on movements of the ground squirrels. Because ground squirrels appeared to use abandoned pocket gopher burrow systems and the location of ground squirrel burrows strongly influenced their aboveground use of habitat, the occupancy of upland habitats by gophers may be an important factor affecting the habitat use characteristics of ground squirrels.


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