Date of Award:
Master of Science (MS)
J. Juan Spillet
This study examined the food interactions between Utah prairie dogs (Cynomys parvidens, Allen) and cattle (Bos taurus), During 1974 and 1975, three prairie dog colonies near Panguitch, Utah, were studied intensely: "Oldfield" was chosen to represent colonies near fields of alfalfa (Medicago sativa); "Lowercrested" was chosen to represent colonies below 2,200 meters above sea level (a. s. 1.) which were not near alfalfa, and "Uppercrested" was chosen to represent colonies above 2,200 meters a.s.l. which have been planted with crested wheatgrass.
Visual observations were made of Utah prairie dogs to determine their diets. Livetrapping of prairie dogs provided data for estimates of population sizes and animal weights, which were used to calculate forage requirements. Cattle diets and forage intake per individual were derived from the literature.
Much more forage was available to prairie dogs than to cattle. About 80 percent of the forb phytomass ingested by prairie dogs at Uppercrested never would have become available to cattle. Prairie dogs foraged more selectively than cattle are capable of doing. Neither animal showed a general dietary preference toward either grasses or forbs: each plant life form contained bath preferred and avoided species. Bath animals had a low preference for shrubs.
Oldfield's area tripled between 1971 and 1974, but Uppercrested did not expand. Between 1 June, 1974, and 1 June, 1975, Oldfield's population increased from about 42 to 70 adult prairie dogs, and the colony's area increased proportionately; however, Uppercrested's population appeared to decline from approximately 22 to 19 adults. The dissimilar expansion rates, at least between 1974 and 1975, probably were due to differences in behavior, forage availability, nutrition, and predation.
Oldfield's prairie dogs gained weight much faster than did Uppercrested's animals. Thus, the average number of active Utah prairie dogs ingesting as much forage as a cow and calf from March through October (prairie dogs fed little during other months) was 410 at Oldfield, compared to 500 at Uppercrested. Numbers concerning total utilization may be even higher: prairie dogs waste little vegetation, but cattle probably trample much. On the other hand, prairie dogs clip closer to the ground and earlier in the growth season than do cattle; consequently, prairie dogs may cause a greater reduction in primary production for the same amount of forage intake.
Population densities of prairie dogs in late June, one month after the young first emerged, were 35/ha at Oldfield, 16/ha at Lowercrested, and less than 2.3/ha at Uppercrested. Prairie dogs used over 70 percent of the primary production of perennial herbage at Oldfield and about 10 percent of it at Lowercrested. Uppercrested's prairie dogs used approximately 3 percent of the primary production of crested wheatgrass, a preferred forage. Within any one year, cattle probably rarely reduce population s of Utah prairie dogs, and possibly may increase populations in colonies with high primary production.
Prairie dogs apparently have reduced the primary production of perennial herbage at bath Oldfield and Lowercrested. Vegetational canopy coverage was greater on mounds than off mounds in the low use portion of Uppercrested. Heavy grazing by livestock in the past probably has eliminated much Utah prairie dog habitat: swales have been destroyed and early spring forage has been reduced.
Crocker-Bedford, Dennis, "Food Interactions Between Utah Prairie Dogs and Cattle" (1976). All Graduate Theses and Dissertations. 7097.
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