Deer-predator relationships: a review of recent North American studies with emphasis on mule and black-tailed deer

In recent years mule (Odocoileus hemionus) and black-tailed (O. h. columbia nus) deer appear to have declined in many areas of the western United State s and Canada, causing concern for population welfare and continued uses of the deer resource. Causes of the decline have not been identified, but pred ation by coyotes (Canis latrans), mountain lions (Puma concolor), and wolve s (Canis lupus) has been proposed as one of many factors. We reviewed results of published studies conducted since the mid-1970s conc erning predator-deer relationships to determine whether predation could be a factor in the apparent deer population declines and whether there was evi dence that predator control could be a viable management tool to restore de er populations. We reviewed 17 published studies concerning mule deer. We f ound only 4 published studies of the effects of predation on black-tailed d eer. A larger database existed for white-tailed deer (O. virginianus), with 19 studies examining effects of predation on white-tailed deer. Study results were confounded by numerous factors. A deer population's rela tionship to habitat carrying capacity was crucial to the impacts of predati on. Deer populations at or near carrying capacity did not respond to predat or removal experiments. When deer populations appeared limited by predation and such populations were well below forage carrying capacity, deer mortal ity was reduced significantly when predator populations were reduced. Only one study, however, demonstrated that deer population increases resulted in greater harvests, although considerable data indicated that wolf control r esulted in greater harvests of moose (Alces alces) and caribou (Rangifer ta randus). The most convincing evidence for deer population increases occurre d when small enclosures (2-39 km(2)) were used. Our review suggests that predation by coyotes, mountain lions, or wolves ma y be a significant mortality factor in some areas under certain conditions. Relation to habitat carrying capacity, weather, human use patterns, number and type of predator species, and habitat alterations all affect predator- prey relationships. Only through intensive radiotelemetry and manipulative studies can predation be identified as a major limiting factor. When it is identified, deer managers face crucial decisions. Reductions in predator densities have occurred only on relatively small stu dy areas (2-180 km(2)) where predators were identified as a major limiting factor and deer populations were well below forage carrying capacity (an im portant criterion). Thus a problem of scale, methods used to kill predators , benefit:cost ratios, results to hunters, and public acceptance are primar y considerations. Methods of predator control available to deer managers ha ve been severely restricted and current methods may not be Feasible over la rge areas when and if predation becomes a problem. Public acceptance of pre dator reduction programs is essential for predator-prey management, but may not be achievable given current public attitudes toward predators. We iden tified several recommendations and research needs based on our review of th e literature given current social and political limitations.