May coyote (Canis latrans) population densities were estimated by three methods on a 700-square-mile study area astride the Utah-Idaho state line during 1966 to 1970. Indices of coyote populations in the spring, summer, and fall of the same years, and in the winter of 1963 to 1966, collectively, provided trend information for the period 1963 to 1970. An estimate of the percentage of female coyotes breeding in 1969 was obtained from a February collection of 19 carcasses in a region surrounding the study area. Estimates of litter sizes and percentages of females breeding in the western third of Utah were obtained from records of the Division of Wildlife Services. Coyote food habits were studied from stomach contents of 186 animals collected in the winters of 1967-68, 1968-69, and 1969-70; and from 111 scats collected year-round, 1966-69. Coyotes in the study area from 1966-70 may have numbered somewhere near 200 or more animals in the 5 years of study. The population declined from its highest index value in 1963 to one-seventh of that value in 1968, then increased substantially in 1969 and 1970. These changes appear to have been correlated with the density of black-tailed jackrabbits (Lepus californicus) the previous year. The causal mechanism may in part have been the effect of jackrabbit density (jackrabbits comprised three-fourths or more of the coyote diet during the period of study) on the coyote reproductive rate, both in terms of litter size and percentage of females breeding. Although most of the observed coyote mortality was man-induced, it represented only a part of the total; hence, the pattern and causes of mortality remain largely unknown. Long-range coyote density appears to be partly a function of the size of the food base, with artificial control doubtlessly playing a part. In this region, where the biota is relatively simple, the jackrabbit constitutes a major part of the food base and therefore is a partial determinant of coyote density. The physiological or behavioral links, or both, are unknown at present.
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