ASSESSING THE IMPORTANCE OF THE MIXED JACK PINE-HARDWOOD COVER TYPE TO THE WINTER DISTRIBUTION, MOVEMENTS, AND SURVIVAL OF WHITE-TAILED DEER IN CAMP RIPLEY, MINNESOTA
STUDY BACKGROUND AND PURPOSE
Management guidelines of the Minnesota Department of Natural Resources (DNR) and other land management agencies integrate forest and wildlife management via practices that attempt to maximize timber productivity and yield, while enhancing wildlife habitat quantity and quality (Thomas 1979, Minnesota DNR 1985). The specific habitat needs of white-tailed deer (Odocoileus virginianus) are a primary consideration when designing timber harvests in northcentral Minnesota. In Minnesota's Forest Zone, conifer thermal cover of deer typically includes dense stands of northern white cedar (Thuja occidentalis), spruce (Picea spp.), and balsam fir (Abies balsamea), and in some areas, jack pine (Pinus banksiana) and red pine (P. resinosa) as well. Current DNR guidelines limit the harvesting of these particular species because of their "value" as winter thermal cover for deer (Minnesota DNR 1985). Winter thermal cover used by free-ranging deer may vary, but generally, it is some combination of vegetation and topography that assists them in maintaining homeothermy. Camp Ripley is located in the Transition Zone of the state, and thermal cover at the Camp is quite different than in the Forest Zone and is characterized by mixed stands of jack pine and hardwoods. A thorough examination of thermal cover (i.e., jack pine) at Camp Ripley (and elsewhere in the Transition Zone) and its value to white-tailed deer is sorely needed.

What is the Winter Energy Challenge of Deer?
Deer at northern latitudes experience wide seasonal changes in nutrition and energy balance with the greatest challenge occurring during winter when food quantity, availability, and quality are diminished (Short et al. 1966, Verme and Ozoga 1971, Mautz 1978). Snow tends to render forage unavailable, and it impedes the mobility of ungulates, thus, having a decreasing effect on food intake, while also imposing increased energetic costs (Verme 1968, Kelsall and Prescott 1971, Moen 1976, Parker et al. 1984, Adamczewski et al. 1986). To maintain positive energy balance during winter, deer must be able to counter heat loss by conduction, convection, radiation, and evaporation with metabolic heat production (Moen 1968a). When winter nutrition is inadequate for sufficient heat production to attain such an energy balance, deer must rely increasingly on physiological, behavioral, and morphological adaptations to minimize heat loss and decrease energy expenditures. During late fall-early winter, deer become hypothyroid and hypometabolic (Hoffman and Robinson 1966, Silver et al. 1969, Seal et al. 1972, Mautz et al. 1992), depend on fat reserves and body protein as alternate energy sources (Torbit et al. 1985, DelGiudice et al. 1990), and grow highly insulative coats (Moen 1968a, Stevens and Moen 1970). Behaviorally, deer may migrate to a winter range, voluntarily restrict their food intake and movements to conserve energy, and they feed primarily during daylight hours (French et al. 1955, Rongstad and Tester 1969, Ozoga and Verme 1970, Moen 1976). Perhaps most important with respect to habitat management considerations, several studies have reported that deer increasingly utilize, and possibly, depend on conifer stands for thermal cover as winter becomes more severe (Cox 1938, Webb 1948, Severinghaus and Cheatum 1956, Gill 1957, Ozoga 1968).

Functional Thermal Characteristics of Dense Conifer Stands.
--Dense stands of conifers modify winter microclimates in a manner that affords enhanced energy conservation capabilities for deer through thermoregulation (Moen 1968a, 1973, 1982; Ozoga 1968; Stevens and Moen 1970; Moen and Evans 1971; Parker et al. 1984). In heavily forested areas, conifer stands with canopies closed >70% affect thermal forces (e.g., wind, radiation) in ways that both directly and indirectly influence the thermal balance of deer. In this habitat type, the wind profile surrounding a deer may be altered in such a way as to significantly reduce convectional heat loss (Stevens and Moen 1970). Conductive heat loss from deer may also be decreased, since diminished wind velocities within conifer stands will be associated with a greater depth of insulative air within the hair layer. Furthermore, a greater downward infrared radiation flux (i.e., heat) within conifer stands than in more open habitat types has been demonstrated on clear nights (Moen 1968a). A deer's radiant surface temperature changes with changes in radiation, wind, and ambient temperature (Moen 1973). As part of the deer's operational environment, conifer cover reduces net radiation loss from the animal.

Additionally, conifer cover influences the energy balance of deer via its decreasing-effects on snow depth and density, and resultant decreased energy expenditures for mobility (Moen and Evans 1971, Moen 1973, Mattfeld 1974). A moderately dense conifer stand may intercept from 15 to 30% of the total winter snowfall (formula: Percent interception = 0.36 x canopy cover [%], [U.S. Army 1956], DelGiudice 1991). The energetic cost to deer of walking through 18 cm of snow is only slightly greater than walking with no snow; however, the cost increases more rapidly as depth increases, and movements become "severely restricted" at approximately 41 cm (Kelsall and Prescott 1971, Mattfeld 1974, Moen 1976). Reduced winds, greater nocturnal downward radiation flux from the canopy, and less diurnal exposure to solar radiation and snowmelt account for snowpacks that are less dense within conifer cover than in more open habitat (Moen and Evans 1971).

The Thermal Value of Mixed Jack Pine-Hardwood Stands?--Far less is known about the relationship between white-tailed deer and the type of thermal cover typically observed at Camp Ripley and elsewhere in the Transition Zone. It is apparent from observations of overbrowsing on winter ranges of deer at Camp Ripley that jack pine, specifically, has a second important value to deer--that is as a source of nutrition. Cursory observations suggest that it may be a more important dietary component there than in the Forest Zone where habitat composition can be appreciably different (DelGiudice 1994).

Flexibility inherent in morphological, physiological, and behavioral specializations of deer to their periodically changing environments permits them to survive in a variety of habitats (Moen 1968b, Ozoga and Gysel 1972, Slobodkin and Rapoport 1974, Seal 1978). Moen (1968a) states that "food is the basic requirement," but as sufficient food becomes less available for fulfilling energy requirements, thermal cover becomes physiologically important as a means of reducing energy lost as heat and for maintaining thermal balance. In western Minnesota, Moen (1966) observed that deer did not seek cover, despite ambient temperatures <18o C (0o F), when adequate food was available to maintain positive energy balance. In eastcentral Ontario, Schmitz (1990) noted that deer maximized energy intake to maximize survivorship, as opposed to minimizing time exposed to adverse weather conditions in open habitats. However, the attributes and responses of these populations represent only a portion of the ecotypic variation within this species (Ruggiero et al. 1988). At Camp Ripley, the higher digestible energy available to deer from crop residue in the agricultural fields juxtaposed to peripheral portions of the Camp compared to that available from natural browse in more interior portions of the Camp, may have a significant influence on how and when deer use the thermal cover distributed over the Camp's landscape and on aspects of their seasonal migration. In addition to the specific source of the digestible energy, the severity of winter weather conditions may strongly influence nutritional restriction (DelGiudice 1996, 1998).

The mixed conifer (i.e., jack pine)-hardwood habitat of the deer's winter range at Camp Ripley may have a third important function for deer, and that is as a refuge from wolf (Canis lupus) predation, thus, contributing to a "balance" between the two species (Nelson and Mech 1981). Recently, timber wolves have moved into and taken up residence within Camp Ripley's boundaries, and preliminary data indicate that their home range is relatively small, possibly due to the high deer densities (L. D. Mech, U.S.G.S., person. commun.). Further, there is an inverse relationship between winter severity and the nutritional condition of deer in Minnesota and a direct relationship between winter severity (e.g., snow depth) and wolf predation (Nelson and Mech 1986; DelGiudice and Riggs 1996; DelGiudice 1996, 1998), which may increase the relative importance of the mixed jack pine-hardwood habitat type to deer during severe winters.

It is not clear where, when, and to what degree the jack pine-hardwood cover type is an essential habitat component or represents a habitat requirement of deer. However, because winter ranges are less available and more intensely used by deer than spring-summer-fall ranges, they are more sensitive to management practices (Thomas et al. 1979). Habitat requirements are described as those habitat components upon which deer depend for survival, but the nature of the dependency such components represent is "dynamic and interactive...in both space and time" (Ruggiero et al. 1988). There has been little study of Camp Ripley's deer, thus reliable information concerning deer-habitat-wolf interactions to serve as a basis for sound management decisions is sparse and sorely needed. It is clear that we must significantly increase our knowledge of the functional relationship that exists between deer and thermal cover in the Transition Zone (i.e., Camp Ripley) under varying environmental conditions to better understand the range of habitats that will fulfill the needs of deer. Important to understanding this relationship, we must become more informed about the interactive roles of nutrition and predation pressure imposed by the recently established wolves. With the increasing interest to harvest jack pine stands within the Camp and the recent commencement of a wolf study, the timing for a study addressing these relationships is critical and wise with respect to the quality of information it would yield in support of the future management of deer. Assuming that evolved preferences for habitat are indicatve of long-term requirements of deer and relate directly to the probability of their persistence (Ruggiero et al. 1988), I believe that the information generated from this study will provide greater insight into the "ecological dependence" of deer on the jack pine-hardwood habitat type for thermal cover in this part of Minnesota.

STUDY OBJECTIVES AND METHODOLOGICAL APPROACH
The goal of this study is to examine the relative influences of winter severity and nutrition on use of the jack pine-hardwood habitat type as winter thermal cover by white-tailed deer in Camp Ripley. My study approach will involve two winter field seasons (winters 1998-99, 1999-2000) for data collection, and an additional half year for data analysis and report preparation. Specific objectives will be to determine or estimate the (1) distribution and home ranges of female deer on winter range, (2) their seasonal migration patterns, (3) habitat composition of their winter home ranges relative to winter severity, (4) average, daily digestible energy intake as winters progress, and (5) age-specific survival and cause-specific mortality rates. Further, we will continue aerial, winter estimates of Camp Ripley's deer population, which were begun during winter 1996-97 as a pilot study.

The basic methodological approach will include two winter study sites. One site will be part of a deer winter range located near the periphery of the Camp, where during winter, deer are known to move out of the Camp on a daily basis to consume crop residue in nearby agricultural fields. The second site will be part of a deer winter range located more at the interior of the Camp, from which deer do not move to agricultural fields for crop residue. Twenty female deer will be captured by netgun shot from a helicopter (Helicopter Wildlife Management, Inc., Salt Lake City, Ut.) on each study site during January 1999. Deer will be chemically immobilized by intramuscular injection of 100 mg xylazine HCl and 300 mg ketamine HCl. A last incisor will be extracted for age determination (Gilbert 1966), eartags will be applied, a radio-collar (with a mortality switch) fitted (Advanced Telemetry Systems, Isanti, Minn.), and anesthesia will be reversed with an intravenous injection of 15 mg yohimbine HCl (Mech et al. 1985).

Survival of all collared deer will be monitored weekly by radio telemetry. Ten collared deer on each study site will be radio-located by triangulation 3-4 times per week through April or spring migration to their spring-summer-fall range. Locations (plotted by UTM coordinates) will be used to determine the deer's winter home range by the adaptive kernal method (Kie et al. 1994).

Habitat composition of the two study sites will be determined by air photointerpretation using color infrared air photos (1:15,840 scale), digital orthophotoquads, and confirmation by ground- truthing. Delineated habitat types and and radio locations of deer will be digitized, and a geographic information system (Arc/Info) will be used to perform temporal and spatial analyses of habitat compositions of the deer home ranges relative to winter severity (i.e., snow depth and penetrability, mean daily minimum and maximum temperatures).

A field method will be employed for estimating mean daily digestible energy intake for deer sustaining themselves solely on natural diets versus those with access to crop residue on agricultural fields located near the Camp.

All mortalities of deer, most of which we expect will occur during winter, will be investigated for cause by collecting and examining carcass and site evidence (DelGiudice and Riggs 1996, DelGiudice 1998). Age-specific survival and cause-specific mortality analyses will be conducted as described elsewhere (DelGiudice and Riggs 1996).

The deer population at Camp Ripley will be estimated using the double survey method of Magnusson et al. (1978), with modifications by Chapman (1951) and Seber (1973:60), conducted from fixed wing aircraft.

LITERATURE CITED
Adamczewski, J. Z., C. C. Gate, B. M. Soutar, and R. J. Hudson. 1986. Limiting effects of snow on seasonal habitat use and diets of caribou (Rangifer tarandus groenlandicus) on Coats Island, Northwest Territories, Canada. Can. J. Zool. 66:1986-1996.

Cox, W. T. 1938. Preventing deer concentrations. J. Wildl. Manage. 2:1-2.

Chapman, D. G. 1951. Some properties of the hypergeometric distribution with applications to zoological censuses. Univ. Calif. Pub. Stat. 1:131-160.

DelGiudice, G. D. 1991. Assessing the relationship of conifer thermal cover to winter distribution, movements, and survival of white-tailed deer in north central Minnesota. Pages 25-35 in B. Joselyn, ed. Summaries of wildlife research findings, 1991. Minnesota Dep. Nat. Resour. St. Paul, MN.

DelGiudice, G. D. 1994. Assessing the relationship of conifer thermal cover to winter distribution, movements, and survival of white-tailed deer in north central Minnesota. Pages 45-63 in B. Joselyn, ed. Summaries of wildlife research findings, 1994. Minnesota Dep. Nat. Resour. St. Paul, MN.

DelGiudice, G. D. 1996. Assessing the relationship of conifer thermal cover to winter distribution, movements, and survival of white-tailed deer in north central Minnesota. Pages 59-81 in B. Joselyn, ed. Summaries of wildlife research findings, 1996. Minnesota Dep. Nat. Resour. St. Paul, MN.

DelGiudice, G. D. 1998. Surplus killing of white-tailed deer by wolves in northcentral Minnesota. J. Mammal. 79:227-235.

DelGiudice, G. D., L. D. Mech, and U. S. Seal. 1990. Effects of winter undernutrition on body composition and physiological profiles of white-tailed deer. J. Wildl. Manage. 54:539-550.

DelGiudice, G. D., and M. R. Riggs. 1996. Long-term research on the white-tailed deer/conifer thermal cover relationship: aligning expectations with reality. Trans. North Am. Wildl. and Nat. Resour. Conf. 54:134-145.

French, C. E., L. C. McEwen, N. D. Magruder, R. H. Ingram, and R. W. Swift. 1955. Nutritional requirements of white-tailed deer for growth and antler development. Pennsylvania Agric. Exp. Stn. Bull. 600, University Park. 50pp.

Gilbert, F. F. 1966. Aging white-tailed deer by annuli in the cementum of the first incisor. J. Wildl. Manage. 30:200-202.

Gill, J. D. 1957. Review of deer yard management 1956. Game Div. Bull. 5. Maine Dep. of Inland Fish and Game, Augusta. 61pp.

Hoffman, R. A., and P. F. Robinson. 1966. Changes in endocrine glands of white-tailed deer affected by season, sex, and age. J. Mammal. 47:266-280.

Kelsall, J. P., and W. Prescott. 1971. Moose and deer behavior in snow. Can. Wildl. Serv. Rep. Ser. 15. 27pp.

Kie, J. G., J. A. Baldwin, and C. J. Evans. 1994. Calhome: home range analysis program. Electronic user's manual. 19pp.

Magnusson, W. E., G. J. Caughley, and G. C. Grigg. 1978. A double-survey estimate of population size from incomplete counts. J. Wildl. Manage. 42:174-176.

Mattfeld, G. F. 1974. The energetics of winter foraging by white-tailed deer--a perspective on winter concentration. Ph.D. Thesis, Syracuse State Univ., N.Y. 306pp.

Mautz, W. W. 1978. Nutrition and carrying capacity. Pages 321-348 in J. L. Schmidt and D. L. Gilbert, eds. Big game of North America: ecology and management. Stackpole Books, Harrisburg, Pa.

Mautz, W. W., J. Kanter, and P. J. Pekins. 1992. Seasonal metabolic rhythms of captive female white-tailed deer: a reexamination. J. Wildl. Manage. 56:656-661.

Mech, L. D., G. D. DelGiudice, P. D. Karns, and U. S. Seal. 1985. Yohimbine hydrochloride as an antagonnist to xylazine hydrochloride-ketamine hydrochloride immobilization of white-tailed deer. J. Wildl. Dis. 21:405-410.

Minnesota Department of Natural Resources. 1985. Forestry- wildlife guidelines to habitat management. St. Paul. 137pp.

Moen, A. N. 1966. Factors affecting the energy exchange of white-tailed deer, western Minnesota. Ph.D. Thesis. Univ. Minnesota, St. Paul. 121pp.

Moen, A. N. 1968a. Surface temperatures and radiant heat loss from white-tailed deer. J. Wildl. Manage. 32:338-344.

Moen, A. N. 1968b. Energy exchange of white-tailed deer, western Minnesota. Ecology 49:676-682.

Moen, A. N. 1973. Wildlife ecology, an analytical approach.

W. H. Freeman and Company, San Francisco, Calif. 458pp.

Moen, A. N. 1976. Energy conservation by white-tailed deer in the winter. Ecology 56:192-198.

Moen, A. N. 1982. The biology and management of wild ruminants. Part V. Meteorology and thermal relationships of wild ruminants. ConerBrook Press, Lansing, N.Y.

Moen, A. N., and K. E. Evans. 1971. The distribution of energy in relation to snow cover in wildlife habitat. Pages 147-162 in A. O. Haugen, ed. Proceedings of symposium on the snow and ice in relation to wildlife and recreation. Iowa State Univ., Ames.

Nelson, M. E., and L. D. Mech. 1981. Deer social organization and wolf predation in northeastern Minnesota. Wildl. Monogr. 77. 53pp.

Nelson, M. E., and L. D. Mech. 1986. Relationship between snow depth and gray wolf predation on white-tailed deer. J. Wildl. Manage. 50:471-474.

Ozoga, J. J. 1968. Variations in microclimate in a conifer swamp deeryard in northern Michigan. J. Wildl. Manage. 32: 574-585.

Ozoga, J. J., and L. W. Gysel. 1972. Response of white-tailed deer to winter weather. J. Wildl. Manage. 36:892-896.

Ozoga, J. J., and L. J. Verme. 1970. Winter feeding patterns of penned white-tailed deer. J. Wildl. Manage. 34:431-439.

Parker, K. L., C. T. Robbins, and T. A. Hanley. 1984. Energy expenditures for locomotion by mule deer and elk. J. Wildl. Manage. 48:474-488.

Rongstad, , O. J., and J. R. Tester. 1969. Movements and habitat use of white-tailed deer in Minnesota. J. Wildl. Manage. 33:366-379.

Ruggiero, L. F., R. S. Holtausen, B. G. Marcot, K. B. Aubry,

J. W. Thomas, and E. C. Meslow. 1988. Ecological dependency: the concept and its implications for research and management. Trans. North Am. Wildl. and Nat. Resour. Conf. 53:115-126.

Schmitz, O. J. 1990. Management implications of foraging theory: evaluating deer supplemental feeding. J. Wildl. Manage. 54:522-532.

Seal, U. S. 1978. Assessment of habitat condition by measurement of biochemical and endocrine indicators of the nutritional, reproductive, and disease status of free-ranging animal populations. Pages 305-324 in Proc. classification, inventory, and analysis of fish and wildlife habitat. Off. Biol. Serv., U.S. Fish and Wildl. Serv., Washington, D.C.

Seal, U. S., L. J. Verme, J. J. Ozoga, and A. W. Erickson. 1972. Nutritional effects on thyroid activity and blood of white-tailed deer. J. Wildl. Manage. 36:1041-1052.

Seber, G. A. F. 1973. The estimation of animal abundance and related parameters. Charles Griffin, London. 506pp.

Severinghaus, C. W., and E. L. Cheatum. 1956. Life and times of the white-tailed deer. Pages 57-186, in W. P. Taylor, ed. The deer of North America. The Stackpole Book Company, Harrisburg, Pa.

Short H. L., D. R. Dietz, and E. E. Remmenga. 1966. Selected nutrients in mule deer browse plants. Ecology 47:222-229.

Silver, H., N. F. Colovos, J. B. Holter, and H. H. Hayes. 1969. Fasting metabolism of white-tailed deer. J. Wildl. Manage. 33:490-498.

Slobodkin, L. B., and A. Rapoport. 1974. An optimal strategy of evolution. Quart. Rev. Biol. 49:181-200.

Stevens, D. S., and A. N. Moen. 1970. Functional aspects of wind as an ecological and thermal force. Trans. North Am. Wildl. and Nat. Resour. Conf. 35:106-114.

Thomas, J. W. 1979. Introduction. Pages 10-21 in J. W. Thomas, ed. Wildlife habitats in managed forests, the Blue Mountains of Oregon and Washington. U.S.D.A. For. Serv. Handbook No. 553, Portland, Oreg.

Torbit, S. C., L. H. Carpenter, D. M. Swift, and A. W. Aldredge. 1985. Differential loss of fat and protein by mule deer during winter. J. Wildl. Manage. 49:80-85.

U.S. Army. 1956. Snow hydrology. Portland, Oreg.: North Pacific Div., Corps of Engineers, U.S. Army. 437pp.

Verme, L. J. 1968. An index of winter weather severity for northern deer. J. Wildl. Manage. 32:566-574.

Verme, L. J., and J. J. Ozoga. 1971. Influence of winter weather on white-tailed deer in Upper Michigan. Pages 16-28 in A. O. Haugen, ed. Snow and ice symposium. Ames, Iowa.

Webb, W. L. 1948. Environmental analysis of a winter deer range. Trans. North Am. Wildl. Conf. 13:442-450. 383pp.

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