Relationships among Mule Deer Fawn Mortality, Coyotes, and Alternate Prey Species during Summer

Abstract

The extent, timing, and causes of summer mortality of mule deer (Odocoileus hemionus) fawns were studied in relation to coyote (Canis latrans) population level, alternate prey population levels, and coyote food habits. Additionally, fawn mortality rates were related to supplementary information on vegetation production and fawn hiding cover. A minimum of 90% of summer mortality of fawns was the result of predation by coyotes. Fawn mortality was lowest when microtine rodent populations were high. Mortality rate of fawns was not directly related to population levels of coyotes, deer mice (Peromyscus maniculatus), white-tailed jack rabbits (Lepus townsendii), or Nuttall's cottontails (Sylvilagus nuttallii). Vegetation production and winter snow cover may have been factors regulating microtine populations and thereby fawn mortality rates. Coyote predation can reduce fawn survival in nutritionally healthy deer populations, but alternate prey population levels and cycle phase should be determined by managers prior to decisions about predator control to increase deer populations. J. WILDL. MANAGE. 48(2):489-499 Mule deer populations associated with timbered breaks-badlands habitats in north-central Montana declined sharply during the early 1970's, apparently as a result of extensive overwinter mortality in 1971-72 followed by low fawn production or survival (R. J. Mackie, unpubl. rep., Mont. Dep. Fish and Game, Fed. Aid Proj. W-120-R-7, 1976). Recruitment remained low into the mid-1970's despite apparently favorable habitat conditions. A similar population decline associated with overwinter mortality during 1964-65 was followed by increased fawn production/survival and population recovery within 2 years (Fig. 1). Concomitant with the decline in deer populations, increases in coyote populations were reported in north-central Montana and elsewhere following the 1972 ban on the use of toxicants, especially compound 1080, in predator control. Although quantitative data on coyote population trends in north-central Montana were lacking, studies by C. J. Knowles (unpubl. rep., Mont. Dep. Fish and Game, Fed. Aid Proj. W-120-R-7, 1976) indicated that predation by coyotes on mule deer was occurring in breaks habitat along the Miss uri River and may have been a major factor affecting fawn recruitment. The fact that fawn: doe ratios were low in early winter further indicated that, if predation was the cause of low recruitment, it was especially important during the summer-fall periods. This study was established during the summer of 1976 to quantify the extent, timing, and causes of summer mortality among mule deer fawns; specifically, the role and importance of coyote predation in fawn recruitment to early winter. Intensive studies were conducted annually from early June through mid-September from 1976 through 1981 as one segment of broader studies on the population ecology and habitat relationships of mule deer I Send reprint requests to senior author at Box 5, Montana State University, Bozeman, MT 59717. J. Wildl. Manage. 48(2):1984 489 This content downloaded from 157.55.39.124 on Fri, 13 Jan 2017 18:13:03 UTC All use subject to http://about.jstor.org/terms 490 MULE DEER, COYOTES, AND ALTERNATE PREY * Hamlin et al.