Special considerations on baiting and feeding deer in Northern Wisconsin: How is concentration over a feeding site different than concentration in a deer yard?
By : Tim Van Deelen, Wisconsin DNR
"Yarding" is a behavioral tactic used by deer in the northern Great Lakes region to cope with severe winter weather. Northern deer typically migrate to and concentrate in traditionally used areas of thick overstory cover (deeryards, often conifer swamp or eastern hemlock) where stand structure provides a buffer against convective heat loss and snow interception and species composition provides nutritious woody browse (e.g. northern white cedar; Verme 1965, Blouch 1984). Critics of efforts to enact a ban on baiting and feeding have argued that, to the extent that concentrating deer increases risk of disease transmission, concentration at a winter feeding site is equivalent to concentration in a winter deeryard. Thus, critics argue that removal of feeding sites does nothing to reduce concentrations of deer during the winter.
Intensity of concentration at feeding sites
Lewis (1990) studied the effects of supplemental feeding of deer near Clam Lake (WI) during the winters of 1987-1989. His data included 855 hours of systematic observations of deer at winter feed sites between December 1 and April 30 (151 days). Observations were made between 4:00pm and 8:00am (16 hours). Lewis (1990) reports that deer use of feeding sites averaged 0.98 deer-hours (number of deer seen x length of time at the feeding site) for each hour of observation (range = 0.49 - 1.45, p. 61). Over the course of a winter, this equates to at least 2,368 deer-hours per feeding site (0.98 x 16 x 151 = 2,368).
The defecation rate of white-tailed deer during winter is used in calculating deer density from over-winter deposition of pellet groups (Bennet et al. 1940). It has been measured at 13 pellet groups/day (0.54/hour) in Michigan (Eberhardt and Van Etten 1956) and 34 pellet groups /day (1.4/hour) in Minnesota (Rogers 1987). Application of these deposition rates to Lewis'(1990) data indicates that at a minimum, a Northern Wisconsin feeding site experiences between 1,279 (2,268 x 0.54) and 3,315 (2,368 x 1.4) deer defecations during a winter.
Over-winter pellet group densities (measured from leaf-fall to green-up [approximately October 15 to April 30]) have been reported for several deer populations. Average pellet group densites were 13/100m2 (526/acre) in Upper Peninsula (MI) deeryards (Van Deelen 1995), 188/acre in northern Wisconsin deeryards (Olson et al. 1955), and 0.00625/m2 (25/acre) in "high-use" Quebec deeryards (Messier and Barrett 1985).
Assume for the sake of convenience that a feeding site in northern Wisconsin represents and acre of land. These data indicate that the intensity of deer use and, hence, the potential for fecal contamination of food on the ground is 2.5 to 6 times higher than in a typical deer yard situation (MI data used for comparison). A quarter of an acre would be equivalent to a circle with a diameter of 120 feet. Using this definition for the size of a feeding site indicates the potential for fecal contamination of food on the ground is 10 to 24 times higher.
Deer foraging behavior
In deeryards, deer eat a variety of woody browse plants and arboreal lichens (Blouch 1984) scattered across a large area. Litterfall provides more biomass than available understory browse in both harvested and unharvested stands and is more nutritious (Ditchkoff and Servello 1998). Food sources in deeryards (litter and natural browse) are widely distributed over a large area and they are not replaced. Moreover, the fine-scale availability of browse shifts throughout the winter in response to snow accumulation and melt-back patterns that are mediated by variation in overstory cover (Schwab et al. 1987).
Foraging by wintering deer is an optimization process. Energy gains associated with eating need to be balanced against energy costs associated with travel and exposure (Moen 1976). Experiments in Ontario deeryards indicate that the goal during winter is to maximize caloric intake as opposed to minimizing exposure (e.g. to predators, harsh weather etc.; Schmitz 1990). Consequently, in a natural deeryard deer diets change over the course of a winter. Deer are highly selective for palatable (nutritious) browse during early winter and become less selective as the most nutritious browse becomes depleted (Brown and Doucet 1991).
Foraging in a natural deeryard is thus a very dynamic phenomena and foraging deer are kept moving in response to a diffuse food source whose availability in space and time is modified by variation in weather, variation in browse species composition, and variation in deer nutritional needs. Moreover, browse available from live plants and blow-downs is typically held aloft on the plant stem such that fecal contamination is less likely and once a mouth-full of natural browse is eaten, it is not replaced before the next growing season (Brown and Doucet 1991).
The establishment of a feeding site where high-calorie food (e.g., corn) is replaced as it is depleted is very different. Deer quickly habituate to patterns of replacement of supplemental food and will alter their foraging behavior to coincide. Experiments in Texas have demonstrated that this change in activity supercedes any influence on deer behavior coming from weather, lunar parameters, etc. (Henke 1997). Deer seeking to maximize caloric intake simply access the supplemental food site as often as possible subject to the amount of food made available and their position in the social hierarchy (Ozoga 1972, Tarr and Pekins 2002). Social factors among groups of deer restrict immediate access to supplemental food sites such that deer "waiting their turn" at the feeding site continue to use natural browse (Schmitz 1990) and browse depletion in the vicinity of a supplemental food site often exceeds that in equivalent habitat without supplemental food sites (Doenier et al. 1997).
Increased small-scale interactions over supplemental food site thus are conducive to the spread of transmissible disease. Aggressive behaviors (fighting, sparring, etc.) are commonly reported (Ozoga 1972, Lewis 1990, Garner 2001). Observations at supplemental food sites in northern Michigan demonstrated 5900 face to face contacts in 355 hours of direct observation (roughly 17/hour; Garner 2001). Garner (2001) documented a particularly alarming behavior among deer using frozen feed piles. Deer used the heat from their mouths and nostrils to dislodge food such that frozen feed piles were dented with burrows made from deer noses. He reported that "Throughout the winter multiple numbers of deer were observed working in and around the same feed piles. I suspect that each deer that feeds this way at a frozen feed pile leaves much of its own saliva and nasal droppings in the field pile at which its working"(Garner 2001, p. 46).
This research is corroborated by studies on the large-scale behavior of radio-collared white-tailed deer with access to supplemental food sites. Garner (2001) monitored 160 radio-collared deer for 2 fall/winter periods in northern Michigan and documented their behavior over feeding sites using both telemetry and direct observations. He demonstrated that, relative to natural forage, supplemental feeding caused reduced home range sizes, increased overlap of home ranges in space and time and dramatic concentrations of activity around feeding sites. In northern Wisconsin, home ranges of winter-fed deer were similar to those existing on natural forage but winter-fed deer were less likely to migrate to separate summer ranges (Lewis 1990, Lewis and Rongstad 1998). Other studies report that deer may or may not alter their entire home range but will dramatically alter their core area use to include supplemental feeding sites (Williams and DeNicola 2000, Kilpatrick and Stober 2002).
Intuitively, supplemental food should increase the over-winter survival of wild deer. However, efforts to study this issue in the upper Great Lakes region are limited to one study. Lewis (1990; Lewis and Rongstad 1998) compared the survival of 3 groups of deer in northern Wisconsin. One group was supplementally fed in the winter, one in the summer, and one existed entirely on natural browse. Feeding had no measurable effect on the survival of bucks. With data pooled across the 3-year study, summer survival was marginally lower for summer-fed does - a phenomena that Lewis (1990; Lewis and Rongstad 1998) attributed to greater vulnerability of summer-fed deer to bait-using hunters. The survival of winter-fed does was equivalent to that of non-fed does. When analysis was restricted to data from the severe winter of 1988-1989, winter mortality was higher for non-fed does with all winter mortality due to winter severity occurring among fawns.
Lewis' (1990; Lewis and Rongstad 1998) study is the only study of its kind on the comparison of survival among groups of free-living deer that were either fed or not-fed. Unfortunately, his analysis was incomplete because it did not account for the confounding effects of age (fawn versus adult) and migratory behavior - effects known to influence the survival of deer in the upper Great Lakes region (Nelson and Mech 1986, 1991; Van Deelen et al. 1997). Nonetheless, analysis relative to supplemental feeding as reported by Lewis (1990; Lewis and Rongstad 1998; e.g. minor effects on survival except for severe winters) is consistent with other research on deer mortality in the upper Great Lakes. For example, Van Deelen et al. (1997) reported high winter survival for adult deer (little or no access to supplemental feed) during a period of mild winters. Despite this, winter starvation was seen in a small number of fawns.
Baker and Hobbs (1985) experimented with supplemental feeding of wild and captive mule deer fawns during an unusually severe winter in Colorado. In their study, feeding improved fawn survival when fawns were fed a carefully crafted blend of soluble carbohydrates and undigestible fiber. The blend was used to avoid supplement-induced digestive impaction and ulceration associated with excess undigestible fiber (e.g. low quality hay) or (often fatal) rumen acicdosis associated with high-energy concentrates (e.g. corn). Baker and Hobbs (1985) acknowledged that feeding likely carried important biological risks (notably disease risk) and that costs (biological and economic) will frequently exceed benefits realized in terms or increase fawn survival. Their "data do not support the use of supplemental feeding to routinely increase the carrying capacity of mule deer range". Instead they "infer that feeding can be used in emergency circumstances to prevent abnormally high mortality resulting from extreme weather conditions" (Baker and Hobbs 1985, p. 941; emphasis added).
Significantly, Lewis (1990; Lewis and Rongstad 1998) correlated long-term feeding operations (several years) with a break down in traditional migration behavior among local deer in Wisconsin. Migration to secure winter yarding areas is a behavior that northern deer use to improve winter survival in the face of harsh winter weather and increased vulnerability to predators (Messier and Barrette 1985, Nelson and Mech 1991, Nelson 1994). This observation is consistent with observations that migration behavior in individuals can be conditional (Nelson 1994) and may be altered to accommodate unusual circumstances (very mild winters, novel food sources such as a winter cutting). A likely mechanism linking winter-feeding to breakdown in migratory behavior is that conditional migrators fail to migrate from the vicinity of the feeding site and consequently do not teach the migratory behavior to their fawns (Nelson 1998).
Lewis (1990; Lewis and Rongstad 1998) compared the recruitment of 2 groups of does in northern Wisconsin. One group was supplementally fed in the winter, one in the summer, a control group that existed entirely on natural browse was not included. In this study, recruitment among summer fed deer was higher than that of winter fed deer. Again, these results are difficult to interpret because the confounding effect of age (fawn versus adult) was not controlled. In a captive research herd in Michigan's upper peninsula, experimental supplemental feeding caused a dramatic increase in the physical condition and reproductive rate of does - especially yearling does (Ozoga and Verme 1982). This increase in reproduction drives an increase in recruitment until the point at which crowding impairs fawn-rearing behaviors and fawn mortality increases to compensate (Ozoga et al. 1982). In fact, the positive relationship between nutrition and recruitment (as mediated by density) is a well-known phenomenon that provides the theoretical basis for sustainable management of hunted deer populations (McCullough 1984, Sinclair 1997). Thus widespread supplemental feeding of deer likely makes herd control in northern Wisconsin more difficult - requiring more use of unpopular hunting programs like T-zones and Earn-A-Buck.
Available science suggests that the disease risks associated with supplemental feeding in northern Wisconsin are significantly higher than the risks associated with the natural concentration of deer in winter deeryards. In addition, population-level effects of supplemental feeding (minor influence on survival, increase in recruitment) likely supports a more abundant deer herd - itself a risk factor and a potential impediment to disease control efforts.
Baker, D. L. and N. T. Hobbs. 1985. Emergency feeding of mule deer during winter: tests of a supplemental ration. Journal of Wildlife Management 49: 934-942.
Bennett L. J., P. F. English, and R. McCain. 1940. A study of deer populations by use of pellet group counts. Journal of Wildlife Management 4:398-403.
Blouch, R. I. 1984. Northern Great Lakes states and Ontario forests. Pp. 391-410 in L. K. Halls (editor) White-tailed deer ecology and management. Stackpole Books. Harrisburg, PA. USA.
Brown, D. T., and G. J. Doucet. 1991. Temporal changes in winter diet selection by white-tailed deer in a northern deer yard. Journal of Wildlife Management 55:361-376.
Ditchkoff, S. S., and F. A. Servello. 1998. Litterfall: an overlooked food source for wintering white-tailed deer. Journal of Wildlife Management 62:250-255.
Doenier, P. B., G. D. DelGiudice, and M. R. Riggs. 1997. Effects of winter supplemental feeding on browse consumption by white-tailed deer. Wildlife Society Bulletin 25:235-243.
Eberhardt, L. L. and R. C. Van Etten. 1956. Evaluation of the pellet-group count as a deer census method. Journal of Wildlife Management 20:70-74.
Garner, M. S. 2001. Movement patterns and behavior at winter feeding and fall baiting stations in a population of white-tailed deer infected with bovine tuberculosis in the northeastern lower peninsula of Michigan. Dissertaion. Michigan State University, East Lansing, MI.
Henke, S. E. 1997. Do white-tailed deer react to the dinner bell? An experiment in classical conditioning. Wildlife Society Bulletin 25:291-295.
Kilpatric, H. J., and W. A. Stober. 2002. Effects of temporary bait sites on movements of suburban white-tailed deer. Wildlife Society Bulletin 30:760-766.
Lewis, T. L. 1990. The effect of supplemental feeding on white-tailed deer in northwestern Wisconsin. Dissertation. University of Wisconsin-Madison, 78pp.
Lewis, T. L., and O. J. Rongstad, 1998. Effects of supplemental feeding on white-tailed deer Odocoileus virginianus, migration and survival in northern Wisconsin. Canadian Field-Naturalist 112:75-81.
Messier, F., and C. Barrette. 1985. The efficiency of yarding behavior by white-tailed deer and an anti-predator strategy. Canadian Journal of Zoology 63:785-789.
Nelson, M. E. 1994. Winter range arrival and departure of white-tailed deer in northeastern Minnesota. Canadian Journal of Wildlife Management 73:1069-1076.
Nelson, M. E. 1998. Development of migratory behavior in northern white-tailed deer. Canadian Journal of Zoology 76:426-432.
Nelson, M. E., and L. D. Mech. 1986. Mortality of white-tailed deer in northeastern Minnesota. Journal of Wildlife Management 50:691-698.
Nelson, M. E., and L. D. Mech. 1991. Wolf predation risk associated with white-tailed deer movements. Canadian Journal of Zoology 69:2696-2699.
McCullough, D. R. 1984. Lessons from the George Reserve. Pp. 211-241 in L. K. Halls (editor) White-tailed deer ecology and management. Stackpole Books. Harrisburg, PA. USA.
Olson, H. F., J. M. Keener, and D. R. Thompson. 1955. Evaluation of deer pellet group count as a census method. Wisconsin Conservation Department Unpublished report.
Ozoga, J. J. 1972. Aggressive behavior of white-tailed deer at winter cuttings. Journal of Wildlife Management 36:861-868.
Ozoga, J. J., and L. J. Verme. 1982. Characteristics of a supplementally-fed deer herd. Journal of Wildlife Management 46:281-301.
Ozoga, J. J., L. J. Verme, and C. S. Bienz. 1982. Parturition of behavior and territoriality in white-tailed deer: impact on neonatal mortality. Journal of Wildlife Management 46:1-11.
Rogers, L. L. 1987. Seasonal changes in the defecation rates of free-ranging white-tailed deer. Journal of Wildlife Management 51: 330-333.
Schmitz, O. J. 1990. Management implications of foraging theory: evaluating deer supplemental feeding. Journal of Wildlife Management 54:522-532.
Schwab, F. E., M. D. Pitt, and S. W. Schwab. 1987. Browse burial related to snow depth and canopy cover in northcentral British Columbia. Journal of Wildlife Management 51:337-341.
Sinclair, A. R. E. 1997. Carrying capacity and the overabundance of deer. Pp. 380-394 in W. J. McShea, H. B. Underwood, and J. H. Rappole (editors). The science of overabundance: deer ecology and population management. Smithsonian Institution Press, Washington D. C.
Tarr, M. D., and P. J. Pekins. 2002. Influences of winter supplemental feeding on the energy balance of white-tailed deer fawns in New Hampshire, USA. Canadian Journal of Zoology 80:6-15.
Van Deelen, T. R. 1995. Seasonal migrations and mortality of white-tailed deer in Michigan's Upper Peninsula. Dissertation. Michigan State University. East Lansing. 158pp.
Van Deelen, T. R., H. Campa III, J. B. Haufler, and P. D. Thompson. 1997. Mortality patterns of white-tailed deer in Michigan's Upper Peninsula. The Journal of Wildlife Management 61: 903-910.
Verme, L. J. 1965. Swamp conifer deeryards in northern Michigan: their ecology and management. J. Forestry 63:523-529.
Williams, S. C., and A. J. DeNicola, 2002. Spatial movements in response to baiting white-tailed deer. Pp. 206-224 in M. C. Brittingham, J. Kays, and R. McPeake (editors). Proceedings of the ninth wildlife damage management conference. Pennsylvania State University, State College PA.
PO Box 255
Roberts WI 54023