Emergency Feeding of Mule Deer during Winter: Tests of a Supplemental Ration

Abstract

We evaluated the efficacy of feeding a supplemental ration to captive and wild mule deer (Odocoileus hemionus hemionus) in Colorado. The supplement was 63% digestible and provided 2.55 kcal/g of metabolizable energy. Ad libitum intake was 28.8 g/kg BW/day. Captive animals adapted to low quality forage diets showed no digestive upsets when abruptly offered the supplemental ration ad libitum. We observed effects of feeding on animal condition and mortality in three populations of wild mule deer. Unfed deer showed the poorest body condition and highest mortality; 53% of the unfed population died during winter. Mortality rates in a population fed 0.9 kg/deer/day averaged 33%; mortality of deer fed ad libitum averaged 24%. We concluded that emergency feeding of a nutritionally adequate ration to mule deer can reduce mortality in populations subject to exceptionally severe winter weather. J. WILDL. MANAGE. 49(4):934-942 Severe winter weather periodically causes high mortality in mule deer populations in the Rocky Mountains. Because such losses are frequently unrelated to population density (Gilbert et al. 1970, Wallmo and Gill 1971, Bartmann and Bowden 1984), they often be ameliorated by harvest management. Habitat improvement and protection of critical wintering areas offer the ultimate solution to this problem (Gilbert et al. 1970, Scotter 1980). However, carrying capacities of traditional winter ranges can vary tremendously due to annual variation in snow depth (Wallmo et al. 1977) and plant production (Hobbs et al. 1982). Consequently, managers must occasionally accept high levels of mortality even on the best managed winter ranges (Crowe and Strickland 1984). This creates an important problem. Inrea ed public demand for mule deer populations d creases the acceptability of high levels of density-independent winter mortality. A potential remedy to this dilemma is feeding deer artificial rations to supplement limited supplies of native forage during unusually harsh winters. In theory, emergency feeding should reduce annual variation in mule deer numbers by mitigating the effects of occasionally severe winter weather. In practice, however, supplemental feeding has usually failed to prevent starvation of deer in the Rocky Mountains (Carhart 1943, 1945; Doman and Rasmussen 1944; Smith 1952; Keiss and Smith 1966). At one extreme, feeding low quality hay caused acute digestive impaction and ulceration (Schoonveld et al. 1974) and limited intake to levels insufficient for maintenance of small bodied ruminants like mule deer (Ammann et al. 1973, Short This content downloaded from 157.55.39.132 on Thu, 15 Sep 2016 06:06:09 UTC All use subject to http://about.jstor.org/terms J. Wildl. Manage. 49(4):1985 EMERGENCY FEEDING OF DEER * Baker and Hobbs 935 et al. 1974). At the other extreme, feeding highenergy concentrates to animals adapted to natural forages caused ruminal acidosis and death (Dean 1973:42-46, Wilson et al. 1975, Wobeser and Runge 1975, Woolfe 1977). These observations led to the widespread belief that wild deer cannot be fed. Initiation of emergency feeding requires that wild deer switch abruptly from natural to supplemental diets. Terminating feeding requires that they switch back. A safe supplemental ration must allow these transitions without causing digestive upsets. Here, we report tests of the efficacy of a supplemental ration for mule deer. We assessed its nutritional value and evaluated its safety when fed to animals adapted to forage diets. We tested the hypothesis that emergency feeding of this ration to mule deer reduced mortality and improved animal condition during an exceptionally severe winter. This research was supported by the Colo. Div. of Wildl. (Game Cash 5060 and Fed. Aid to Wildl. Restoration Proj. 45-01-502-15050). We thank P. H. Neil for assistance in feeding trials, and J. A. Gerrans, A. H. Chappel, B. C. Thompson, and D. J. Freddy for help in the field. R. C. Walsh provided information for economic analysis; J. C. Demander and M. L. Stevens conducted laboratory analysis; D. C. Bowden designed mortality samples; and L. E. Lovett prepared the manuscript. We appreciate reviews of early drafts by J. M. Peek, A. E. Anderson, D. M. Crowe, G. D. Bear, and D. F. Reed.