Light Penetration in Relation to Small Mammal Abundance

Microtus pennsylvanicus usually seems to be most abundant in the heaviest grassy cover of an area. Eadie (Jour. Mamm., 34: 263–264, 1953), reported on relative vole abundance in a quarter-acre quadrat of an uncut timothy field. He found that the area of high mouse numbers as measured by bait acceptance “… had almost twice as much vegetative cover as the area of low acceptance.” To measure cover he air dried and weighed all vegetation taken from small random plots in the “high” and “low” areas. I decided to see if the same general results would be obtained using the “dropping board” method (4 in. × 4 in. squares of ¼ in. plywood—Emlen et al. in MS.). The “Grady Tract” of the University of Wisconsin Arboretum, where this work was carried out, includes a large “man made” though quite typical long grass prairie and also an area of “unimproved” grassland. One hundred numbered dropping boards were placed 30 paces apart along three parallel lines transecting both types of herbaceous vegetation. Records were not complete for three boards, hence the calculations for this paper are based upon 97 of the 100 boards.