In a 7—year study on Black Mesa, Colorado, elevation 10,000 ft 2,4—D herbicide treatment initially reduced forb abundance and northern pocket gopher (Thomomys talpoides) populations 80% to 90%. Both forbs and pocket gophers remained at low levels on one area but returned to pretreatment levels on the other area. The decline in pocket gopher numbers was caused by an inability to survive where their preferred food (forbs) was eliminated by herbicide treatment. The decline was not caused by movements of the animals from sprayed areas, or by direct or indirect toxicity of 2,4—D. The common grasses offer, at best, only a marginal diet for northern pocket gophers; only succulent grasses or those bearing corms or rhizomes yield a subsistence diet. Limited sampling did not indicate that the spray treatment affected the numbers of other small mammals.

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Highlight: Two established prairie dog colonies in Montana were studied to determine the effect of range treatment with 2,4-D on prairie dogs' diet. One colony was sprayed with 2,4-D for 2 consecutive years and the other was not treated. There was a significant reduction in foliar cover by forbs and shrubs on the treated colony but no change on the untreated colony. Foliar cover by grass did not change significantly on either area. Prairie dog diet changed significantly from forbs to grass after forb coverage was reduced. Before spraying, prairie dogs ate 73% forbs and 5% grass. Afterward, they ate 9% forbs and 82% grass. The availability of these foods appeared to be responsible for the diet change. Despite the change in diet, the 2,4-D treatment appeared to have little detrimental effect on prairie dogs. They remained in good condition after treatment, as indicated by body weight, and there was no significant difference in prairie dog activity between the treated and untreated colonies. There was considerable variation in diet between the two colonies the first year, with the prairie dogs preferring grass in the untreated colony and forbs in the treated colony. However, in later years preference values were higher for grass than for forbs on both colonies. Research findings on the diet of black-tailed prairie dogs (CJYW~JS ludovicianus) are divided into two groups. One group contends that forbs

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