Examining Deer and Elk in the Western States with Recovering Gray Wolf Populations: A Landscape-Scale Retrospective Review
The intent of this review is to examine the current and historical status of three native deer taxa (mule deer, Columbian black-tailed deer, and white-tailed deer) and two native elk taxa (Roosevelt and Rocky Mountain elk) across their range in the western United States with recovering gray wolf populations. It identifies the natural and human-related factors keeping these ungulate population levels in check and specifically addresses the role of wolves in driving current population trends. Results suggest that habitat restoration rather than predator control has the highest potential to produce healthy deer and elk populations throughout the west given the current major limitations on each species. Loss of available habitat due to human expansion, changes in forest management practices, and noxious weed invasions have progressed across the study area. Habitat fragmentation also poses an ever-increasing problem for ungulates that are forced to deplete critical fat reserves as they must move farther to forage and find security cover. The major watersheds of the Northern Rockies have been heavily altered over the past several decades by exceptional declines in spring and summer precipitation, harsh winter episodes, a lengthening of the fire season compounded by long-term drought, and perhaps changes in atmospheric circulation patterns over the North Pacific Ocean. Weather and habitat condition continue to drive major population trends on both the Cascade and Rocky Mountain landscapes while hunter harvest remains the primary source of additive mortality given high rates of removal of adult female elk. Mortality related to wolves and other large predators has been shown by several studies to be largely compensatory, or within the range of harvestable surplus. Without serious attention to road/access closures, noxious weed treatment, and a return to the natural fire regime big game will continue to struggle in areas with degraded habitat with or without predator removal programs.
In 1986 a pack of gray wolves from Alberta, Canada established territory in the North Fork Flathead River Valley of northern Montana and was the first pack to return to the western United States in over 50 years. A decade later a small experimental population of 66 wolves related to the Alberta migrants (Canis lupus irremotus) was introduced to central Idaho and Yellowstone National Park. They flourished under the protection provided by the 1973 Endangered Species Act and now inhabit much of what remains of their historic natural habitat in the Rocky Mountains. Since the controversial return of the wolf in the 1990s the question has been asked, “Are they likely to trigger dramatic prey declines?” This review seeks to answer that question by examining deer and elk population trends in western states where wolf recovery is taking place.
Deer and elk are the west’s premier big game species. They provide hunting and recreational viewing opportunity to thousands of people every year and are cornerstones of the Pacific Northwest and Intermountain West landscapes. As such they serve as excellent indicator species of the long-term ecological and social consequences of wolf recovery in the United States. This review addresses the primary factors found to be limiting their survival and recruitment, including the role of wolves in driving population trends.
Materials and Methods
The study area includes the five western states in the lower 48 with established gray wolf populations, namely Washington, Oregon, Idaho, Montana, and Wyoming. The state government wildlife agencies responsible for managing deer and elk within each state produce species-specific management plans that contain measurable goals defined according to existing population levels, habitat potential, desired harvest opportunities, and modeling projections. With exception, the Wyoming Game and Fish Department (WGFD) has not produced any deer or elk management documents and instead regularly adjusts objectives for individual Herd Units based on the most recent harvest and survey trends. Each of the five agencies also releases periodic progress and status reports that contain population censuses, adjusted management strategies, and relevant research findings. Peer-reviewed literature has been collectively analyzed and integrated into the following review in order to delimit the impact of various natural and human-related factors on deer and elk.
A History on the Landscape
European settlement and westward expansion brought with it logging activity and predator control that at first increased the landscape’s carrying capacity for ungulates, but populations of deer and elk quickly plummeted due to unrestricted hunting. By the turn of the 20th century the deer population was near extinction and elk herds had been reduced to living in isolated pockets across the landscape. Deer quickly rebounded with conservative hunting restrictions, land clearing, a lack of major predators, and several translocation efforts. By the 1950s they were so numerous that planned reductions began. Elk numbers dwindled until the latter half of the 20th century when statewide enhancement efforts, reduced deer densities, and increases in available habitat allowed for steady growth.
“The whole continent was one continuing dismal wilderness, the haunt of wolves and bears and more savage men. Now the forests are removed, the land covered with fields of corn, orchards bending with fruit and the magnificent habitations of rational and civilized people.”
– John Adams (1756)
Deer: While numerical estimates of deer are not known, they have expanded their geographic range and are thought to exceed pre-settlement densities by four to ten times depending on locale.[i],[ii] There are two species comprising four subspecies of deer within the study area: mule deer (Odocoileus hemionus hemionus), Columbian black-tailed deer (O. hemionus columbianus), white-tailed deer (O. virginianus idahoensis), and the endangered Columbian white-tailed deer (O. virginianus leucurus). White-tailed deer and mule deer inhabit the east side of the Cascade Mountain Range while black-tailed deer are found west of the Cascade crest. Columbian white-tailed deer are restricted to isolated range along the lower Columbia River where wolves are not present and as such have not been included in this analysis.
Elk: Today roughly 365,000 or more elk roam the northern Rocky Mountain portion of the study area. An additional 115,000 plus roam the Cascades and coastal range of western Washington and Oregon. Two subspecies of elk inhabit the study area. Rocky Mountain elk (Cervus elaphus nelsoni) are found primarily east of Washington and Oregon’s Cascades crest and are distributed throughout the northern Rocky Mountains. Roosevelt elk (C. elaphus roosevelti) occur west of the Cascades Crest. The two subspecies differ slightly in size and morphology but are otherwise quite similar and are able to interbreed.
Emerging science has brought into question long-standing research that may have provided an oversimplified view of ecosystem dynamics in the Pacific Northwest and Intermountain West. Historically, ungulates bounced back rapidly from episodes of overharvest, severe winters, or other major disturbance, but since the latter part of the 20th century patterns of dramatic population depression sometimes lasting a decade or more following a major disturbance have emerged in certain herds. Moreover, herds once thought to be permanent residents in localized areas are shifting their distribution and migration patterns in response to a changing landscape. Their collective response to disturbance has become more conspicuous for three key reasons: an overarching reduction in the quantity and quality of available habitat, amplification in large-scale weather anomalies, and an increasing complex of predators on public lands.
Land Use – Over half a century of fire suppression has caused dramatic departures from the historical natural fire regime on national forest system lands. It has also facilitated conifer encroachment on protected roadless and wilderness lands that provide vast tracks of relatively secure habitat for wildlife, thereby reducing the states’ carrying capacities for deer and elk. Suppression of small fires has caused an accumulation of fuels that increase the potential for extensive high-intensity fires that scorch the landscape and delay regrowth.[iii] Several large, moderate-severity fires occurred in northern Idaho and Montana in the 1990s and early 2000s that have improved habitat conditions for elk.
On non-wilderness federal lands timber harvest has actively replaced wildfire as the primary disturbance regime. Logging reductions in the Idaho Panhandle and Clearwater River Basin and in Oregon and Washington west of the Cascade Crest have resulted from a change in public attitudes towards clear-cutting and old-growth harvest that emerged in the 1970s and 1980s, a decline in the market demand for timber products in the late 2000s, and new research and federal plans/incentives that favor more limited restoration thinning activities. Habitat potential has improved where prescribed stand thinning and forest restoration activities still occur while forage production, and thereby fawn and calf recruitment, have declined where both thinning and natural wildfires have not occurred.
Noxious weeds, particularly spotted knapweed, have proliferated on winter ranges and present one of the largest threats to habitat productivity.[iv] Studies have shown reductions of up to 98% in elk use of rangelands heavily infested with noxious species and dramatic increases in use of ranges where species are removed.[v],[vi] Agriculture, livestock grazing, and expanding urban centers now dominate low-elevation ranges that are critical to ungulate survival during winter. Development activity throughout the west since 1950 has influenced mule deer habitat both directly by reducing available habitat in winter and summer ranges, and indirectly by changing fire dynamics in those ranges.[vii] In Wyoming rapidly expanding oil/gas fields are further contributing to winter range losses.
Vulnerability to mortality is furthered by a combination of influences such as avoidance behavior near roads, mortality caused by vehicle collisions, and illegal poaching.[viii],[ix],[x] Research conducted in northern Idaho estimated that 18% of all cow elk hunting mortality was attributable to poaching, which has been shown to rise with increasing road densities.[xi],[xii] Off-highway vehicle (OHV) registration and illegal access to restricted areas by OHV operators during the hunting season has increased remarkably since the 1990s and may surpass any other human land use activity in promoting elk vigilance[xiii],[xiv]. For mule deer, motorized vehicle disturbance tends to displace them to marginal habitats with less available forage and high exposure to inclement weather. [xv]
Climate – Mule deer inhabit highly variable climates and have become more susceptible to winter die-offs as a consequence of loss and fragmentation of critical winter range. White-tailed deer have a higher potential maximum rate of increase and are less susceptible to over-harvest and habitat loss but are more sensitive to harsh winters. Survival in both deer and elk across the northern montane environments of the study area was heavily impacted by the severe winters of 2009 and 2010 and responded positively to mild winters in subsequent years.
Although ungulate survival throughout western North America is often driven by snowfall and winter precipitation, variation in adult female pregnancy rates, juveniles-at-heel in late autumn, and spring recruitment are heavily influenced by summer forage production, which determines adult female nutritional condition and juvenile body mass entering winter.[xvi] April 1st snowpack has declined at an unprecedented rate in the northern Rockies and Greater Yellowstone regions since the late-20th century and is expected to continue to decline due to positive reinforcement of anthropogenic warming.[xvii],[xviii] Ungulates are in the poorest physical condition of the year immediately prior to the spring “green-up” in late-April, early-May when snowmelt and abundant runoff occur, leading to a sudden increase in available forage. Earlier green-ups can have serious detrimental effects on migratory elk herds that delay migration following harsh winters or are forced to winter on higher-elevation ranges.[xix],[xx]
Significant changes in fire season (July-September) precipitation trends in the Northern Rockies have also occurred since the 1980s.[xxi] Precipitation declined throughout Idaho and Montana from 1982 to 2006, resulting in extreme drought conditions in the Rocky Mountain States in the mid-2000s and potentially intensifying fire activity. The fire season also appears to be getting longer. Precipitation events that occur in October and signal the end of the fire season are occurring, on average, 15 days later in the year, which has the potential to increase fuel accumulation and the length of time that fuels actively burn. Drought and extensive fires in the desert and grassland environments have caused declines that are expected to persist through 2014 and may have altered herd distributions on a local scale.
Factors of large-scale climatic variability have traditionally been examined using Pacific Decadal Oscillation (PDO) and El Nino Southern Oscillation (ENSO) indices. Numerous studies have linked PDO and ENSO to fluctuations in snow depth, stream discharge, and fires in the northwest, but few have examined the effects of these sea surface anomalies on ungulate populations. A recent study conducted in Banff National Park in southern Alberta found that elk population growth rate was primarily limited by the North Pacific Oscillation (NPO), which drives atmospheric currents from the arctic down through the Rocky Mountains.[xxii] A correlation between negative peak anomalies in the NPO and record high years of statewide elk harvest in Idaho, and equally correspondent positive peak anomaly phases and major declines in successful harvest across the state indicate a potential climate limitation on Rocky Mountain elk that warrants further research.
Predation – Hunter harvest accounts for the largest source of “predation” mortality in both the Cascades and Rocky Mountains, contributing to the removal of roughly 10-20% of the ungulate populations annually. Furthermore, it has been shown by several studies to be the only source of additive elk mortality across North America due to high rates of removal of prime-aged reproducing females.[xxiii],[xxiv] Removing adult females, which is formally recognized as antlerless harvest, effectively regulates the size, composition, and reproductive rates of a herd and is the most widely-used population control technique employed by wildlife managers today. It is important to note when discussing hunter harvest that hunters provide over $100 million a year for wildlife management through a tax on the purchase of firearms, ammunition, or archery equipment established by the Pittman-Robertson Act of 1937 and millions more through license and public access fees every year.
Predator kills can exceed hunter kills, especially in primitive areas, but remain largely compensatory as predators tend to focus on young, sick, and older individuals with low reproductive value.[xxv],[xxvi] Research has shown that non-human predators do have the potential to produce additive components of mortality in populations well below forage carrying capacity, nutritionally stressed populations, or during/after severe winters.[xxvii],[xxviii] Additive mortality is also possible in multi-predator complexes. Elk herds in the Idaho primitive area, west-central Montana, and the Greater Yellowstone area may be experiencing population depression due to high predator:prey ratios with multiple predators present. In systems with wolves and no grizzly bears, mountain lion and black bear predation are the dominant sources of calf mortality.[xxix],[xxx] In systems with wolves and grizzly bears, mountain lion predation has tended to decline due to a shift in niche space towards mule deer on steeper slopes. Grizzly bears thereby became the major source of calf mortality.[xxxi],[xxxii],[xxxiii],[xxxiv]
A recent study conducted in northwest Wyoming investigated whether non-consumptive risk effects (i.e. increased elk vigilance and avoidance) caused by the presence of wolves were significant enough to affect elk population growth.[xxxv] Although elk vigilance and avoidance increased when wolves were within 1 km, the frequency of encounters between elk and wolves was not high enough to significantly affect elk body fat, condition, and pregnancy rates. Thereby wolf predation impacts on elk population growth are likely limited to direct consumptive effects.
The results of this review of deer and elk dynamics in the Cascades and northern Rocky Mountains suggest that population dynamics for the five subspecies under consideration are being driven primarily by habitat deterioration (human disturbance, forest management practices, and noxious weed invasions), recent climate anomalies, and direct mortality caused by hunting. Urban development, motorized access, increasing predator numbers, and localized disease have also influenced fitness and survival to a lesser degree. With respect to wolves, the aforementioned research summarized in this report indicates that non-human predators are not a significant source of additive mortality or increased vigilance in deer and elk compared with other factors. Therefore predator control as a management tool will have limited impact on addressing low juvenile recruitment and is not a priority. Adaptive management strategies that aim to restore habitat and improve the quality and abundance of native wildlife species have the highest potential to produce healthy ecosystems throughout the west in the face of a rapidly changing landscape.
[i] Rooney, Thomas P. “Deer impacts on forest ecosystems: a North American perspective.” Forestry 74.3 (2001): 201-208. Print.
[ii] Kalisz, Susan, Rachel B. Spigler, and Carol C. Horvitz. “In a long-term experimental demography study, excluding ungulates reversed invader’s explosive population growth rate and restored natives.” Proceedings of the National Academy of Sciences 111.12 (2014): 4501-4506. Print.
[iii] Rollins, Matthew G., Thomas W. Swetnam, and Penelope Morgan. “Evaluating a century of fire patterns in two Rocky Mountain wilderness areas using digital fire atlases.” Canadian Journal of Forest Research 31.12 (2001): 2107-2123. Print.
[iv] Kelsey, Rick G., and Laura J. Locken. “Phytotoxic properties of cnicin, a sesqiterpene lactone from Centaurea maculosa (spotted knapweed).” Journal of Chemical Ecology 13 (1987): 19-33. Print.
[v] DiTomaso, Joseph M. “Invasive weeds in rangelands: species, impacts, and management.” Weed Science 48.2 (2000): 255-265. Print.
[vi] Olson, Bret E. “Impacts of noxious weeds on ecologic and economic systems.” Biology and management of noxious rangeland weeds. Oregon State University Press, Corvallis, OR (1999): 4-18. Print.
[vii] Rachael, John. Project W-170-R-34 Progress Report, Mule Deer, Study I, Job 2, July 1, 2010 to June 30, 2011. Boise: Idaho Department of Fish and Game, Wildlife Bureau, 2011. Print.
[viii] Swenson, Jon E. “Effects of hunting on habitat use by mule deer on mixed-grass prairie in Montana.” Wildlife Society Bulletin (1982): 115-120. Print.
[ix] Johnson, Bruce K., Michael J. Wisdom, and John G. Cook. “Issues of elk productivity for research and management.” The Starkey Project: a synthesis of long-term studies of elk and mule deer. Reprinted from the 2004 Transactions of the North American Wildlife and Natural Resources Conference, Aliance Communications Group, Lawrence, Kansas, USA (2005): 81-93. Print.
[x] McCorquodale, Scott M. A Brief Review of the Scientific Literature on Elk, Roads, & Traffic. Olympia: Washington Department of Fish and Wildlife, 2013. Print.
[xi] Leptich, David J., and Peter E. Zager. Road access management effects on elk mortality and population dynamics. In Proceedings Elk Vulnerability Symposium, eds. A. G. Christensen, L. J. Lyon, and T. N. Lonner, 126-131. Bozeman: Montana State University, 1991. Print.
[xii] Cole, Eric K., Michael D. Pope, and Robert G. Anthony. “Effects of road management on movement and survival of Roosevelt elk.” The Journal of wildlife management (1997): 1115-1126. Print.
[xiii] Ciuti, Simone, et al. “Effects of humans on behaviour of wildlife exceed those of natural predators in a landscape of fear.” PloS one 7.11 (2012): e50611. Print.
[xiv] United States. Oregon Department of Fish and Wildlife. Oregon’s Elk Management Plan. Salem: Oregon Department of Fish and Wildlife, Wildlife Division, 2003. Print.
[xv] Mule Deer Working Group. Range-wide Status of Mule Deer and Black-tailed Deer – 2013. Tuscon: Mule Deer Working Group, Western Association of Fish and Wildlife Agencies, 2013. Print.
[xvi] Johnson, Bruce K., Priscilla K. Coe, and Richard L. Green. “Abiotic, bottom-up, and top-down influences on recruitment of Rocky Mountain elk in Oregon: A retrospective analysis.” The Journal of Wildlife Management 77.1 (2013): 102-116. Print.
[xvii] Pederson, Gregory T., et al. “The unusual nature of recent snowpack declines in the North American Cordillera.” Science 333.6040 (2011): 332-335. Print.
[xviii] McCabe, Gregory J., and Martyn P. Clark. “Trends and variability in snowmelt runoff in the western United States.” Journal of Hydrometeorology 6.4 (2005): 476-482. Print.
[xix] Wilmers, Christopher C., et al. “Climate and Vegetation.” Yellowstone’s Wildlife in Transition (2013): 147. Print.
[xx] United States. Natural Resources Conservation Service (NRCS), and Wildlife Habitat Council. Fish and Wildlife Habitat Management Leaflet: American Elk (Cervus Elaphus). Publication no. 11. N.p.: United States Department of Agriculture (USDA), 1999. Print.
[xxi] Hadlow, Ann M., and Carl A. Seielstad. Changes in Fire Season Precipitation in Idaho and Montana from 1982-2006. Rep. Missoula: National Center for Landscape Fire Analysis, University of Montana College of Forestry and Conservation, 2009. Print.
[xxii] Hebblewhite, Mark. “Predation by wolves interacts with the North Pacific Oscillation (NPO) on a western North American elk population.” Journal of Animal Ecology 74.2 (2005): 226-233. Print.
[xxiii] Brodie, Jedediah, et al. “Relative influence of human harvest, carnivores, and weather on adult female elk survival across western North America.” Journal of Applied Ecology 50.2 (2013): 295-305. Print.
[xxiv] Vucetich, John A., Douglas W. Smith, and Daniel R. Stahler. “Influence of harvest, climate and wolf predation on yellowstone elk, 1961‐2004.” Oikos 111.2 (2005): 259-270. Print.
[xxv] Eberhardt, L. L., et al. “A Seventy‐Year History of Trends in Yellowstone’s Northern Elk Herd.” The Journal of Wildlife Management 71.2 (2007): 594-602. Print.
[xxvi] Dusek, Gary L., Alan K. Wood, and Shawn T. Stewart. “Spatial and temporal patterns of mortality among female white-tailed deer.” The Journal of Wildlife Management (1992): 645-650. Print.
[xxvii] Ballard, Warren B., et al. “Deer-predator relationships: a review of recent North American studies with emphasis on mule and black-tailed deer.” Wildlife Society Bulletin (2001): 99-115. Print.
[xxviii] Singer, Francis J., et al. “Density dependence, compensation, and environmental effects on elk calf mortality in Yellowstone National Park.” The Journal of Wildlife Management (1997): 12-25. Print.
[xxix] United States. Montana Fish, Wildlife & Parks. Bitterroot Elk Project Progress Report Fall 2012. Helena: Montana Fish, Wildlife & Parks, Wildlife Division, 2012. Print.
[xxx] United States. Idaho Department of Fish and Game. “Many Factors Influence Elk Numbers and How Elk are Managed.” Idaho Fish and Game News 25.7 (2013): 2. Print.
[xxxi] Griffin, Kathleen A., et al. “Neonatal mortality of elk driven by climate, predator phenology and predator community composition.” Journal of Animal Ecology 80.6 (2011): 1246-1257. Print.
[xxxii] Bartnick, T. D., et al. “Variation in cougar (Puma concolor) predation habits during wolf (Canis lupus) recovery in the southern Greater Yellowstone Ecosystem.” Canadian Journal of Zoology 91.2 (2013): 82-93. Print.
[xxxiii] Hamlin, Kenneth L., Julie A. Cunningham, and Kurt Alt. “Monitoring and assessment of wolf-ungulate interactions and population trends within the Greater Yellowstone area, southwestern Montana, and Montana statewide.” Rocky Mountain Wolf Recovery Annual Reports 28 (2009). Print.
[xxxiv] Barber-Meyer, Shannon M., L. David Mech, and Patrick James White. “Elk calf survival and mortality following wolf restoration to Yellowstone National Park.” Wildlife Monographs 169.1 (2008): 1-30. Print.
[xxxv] Middleton, Arthur D., et al. “Linking anti‐predator behaviour to prey demography reveals limited risk effects of an actively hunting large carnivore.” Ecology letters 16.8 (2013): 1023-1030. Print.