Date of Award:

5-1979

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Committee Chair(s)

Fred Knowlton

Committee

Fred Knowlton

Abstract

Coyote-prey relationships were examined in Curlew Valley, northern Utah and southern Idaho, during a period of low jackrabbit density (from September 1973 to May 1975). The Utah and Idaho portions of Curlew Valley were treated separately. Field work provided estimates of relative and absolute rodent densities as well as relative coyote density each spring and fall. Laboratory analysis of over 2,300 scats and 249 stomachs provided detailed information on coyote diets. Jackrabbit population data for northern Utah were obtained from L. Charles Stoddart.

Four species, Peromyscus maniculatus, Perognathus parvus, Eutamias minimus, and Dipodomys ordii comprised over 90 percent of the rodent individuals snap trapped. Estimated mean densities were greatest for Peromyscus (3.3-5.3/ha), and progressively less for Perognathus (2.3-3.6/ha), Dipodomys (0.5-1.8/ha), and Eutamias (0.5-0.7/ha).

Jackrabbits comprised half the annual diet of coyotes in Utah, but only 10 percent in Idaho, where rodents were the principal prey consumed. Marked seasonal and site-specific variation in rodent and jackrabbit consumption occurred in both areas. Seasonal trends probably resulted from changes in rodent abundance and availability.

Relative coyote densities did not vary appreciably during the period and were greater in the Idaho portion of the study area.

Despite low jackrabbit densities in 1973-1975, jackrabbit comprised two-thirds or more of the coyote's diet in Utah during the late fall and winter. This suggests a dearth of available alternate prey at that time. A clumped dispersion of jackrabbits during the winter may have contributed to this phenomenon.

In Utah, coyote utilization of some rodents was correlated with snap trap indices, suggesting that: (1) coyote predation upon these rodents was a random event, or (2) rodent density changes were not of sufficient magnitude to alter coyote predatory behavior. In Idaho, a three-fold increase in pocket gopher and cottontail consumption compensated for a reduction in the availability of deer and microtine rodents.

The importance of various prey species in the diet was compared with their relative densities. Jackrabbit appeared to be "preferred" over rodent; within the rodent group Microtus and Lagurus, Reithrodontomys, Perognathus, and Dipodomys were preferred over Peromyscus and Eutamias. Implied prey preferences are explained principally on the basis of optimization theory, and the significance of prey dispersion patterns is emphasized.

Winter food supply is suggested as the critical factor limiting coyote densities in Curlew Valley and throughout the Great Basin. Availability of jackrabbit, livestock carrion, and to a lesser extent, deer, microtine rodents, and cottontails is likely to be most influential in determining coyote density in the Great Basin Desert.

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