Mule Deer

The Deer That Lewis Named:

Mule Deer and the Uneasy Arithmetic of Montana Wildlife

A Species Described on the Missouri

On May 10, 1805, a northwest wind forced the Corps of Discovery to tie up on the south bank of the Missouri River, at a bend now beneath Fort Peck Reservoir (Lewis, "May 10, 1805"). The captains sent hunters into the hills to look for Assiniboine camps, which they did not find. The hunters returned with two mule deer, a white-tailed deer, two buffalo, and five beaver. That evening Meriwether Lewis wrote a detailed field description of the mule deer, an animal the party had already been killing.

Lewis judged it about a third larger than the common deer, with a wider difference in size between buck and doe. He measured the ears of one large buck at eleven inches long and noted that the antlers fork into equal branches instead of sprouting points from a single main beam. He also recorded the white rump patch and the black-tipped tail. French boatmen called the animal the black-tailed deer, a name Lewis thought poorly chosen because most of the tail is white. The party instead adopted "mule deer," comparing the ears to a mule's (Lewis, "May 10, 1805").

His remarks on habitat were equally precise. Mule deer, he wrote, were rarely found outside rough country and preferred open ground. When flushed from river-bottom timber they ran for the hills, as elk do. He reasoned that the animals, together with three bighorn sheep seen that day, meant the expedition was nearing broken or mountainous terrain. Sergeant John Ordway's entry for the same day recorded "moose deer," which the editors of the journals take to be a slip for mule deer (Lewis, "May 10, 1805"). On May 18, near the Musselshell River, Clark killed four deer, two of them mule deer (Lewis, "May 18, 1805").

Deer Without a Ledger, 1865 to 1900

For the next ninety years the sources consulted for this article say little about mule deer as a species. Nineteenth-century records generally speak of "deer" without distinguishing between mule and white-tailed.

Regulation arrived slowly. The 1865 territorial legislature took Montana's first steps toward protecting wildlife, though Montana Fish, Wildlife & Parks (FWP) describes those measures as aimed at fishing methods (Dickson 32-34; Hagerman-Benton). Closed seasons on big game followed in the early 1870s. The two sources disagree on the year, one giving 1872 and the other 1873. In 1895 the legislature created a Board of Game and Fish Commissioners and set Montana's first harvest limits, which allowed a hunter eight deer (Dickson 32-34; Tabish).

The limits followed a period of heavy pressure. Hunting and fishing parties were arriving in the Flathead region by the early 1890s (Tabish). One account holds that two Demersville residents killed 1,500 deer in three months near the Flathead and Swan rivers, selling the skins for thirty cents each. That figure comes from a single newspaper source, and it does not name the species (Tabish). FWP's own history says that during the nineteenth century bison were nearly eliminated and beaver trapped to scarcity. Elk, pronghorn, deer, and bighorn sheep vanished from much of their former range (Dickson 32-34). In 1900, L. H. Mills of Saco answered a Board of Game and Fish questionnaire by saying that deer were being rapidly exterminated and were hunted with dogs (Dickson 32-34).

Wardens, Licenses, and a Closed East, 1900 to 1960

The 1895 law let counties hire their own wardens, and the arrangement failed. By 1900 only five of the state's twenty-four counties had one. Morton J. Elrod, the University of Montana biologist who chaired the game board, reported that county commissioners had shown no interest in protecting game (Dickson 32-34). In spring 1901 the legislature created a state department under a state fish and game warden. W. F. Scott took the post, hired eight deputies within two months, and began enforcing roughly a dozen game regulations (Dickson 32-34; Hagerman-Benton). Resident hunting licenses became mandatory in 1905 (Dickson 32-34; Hagerman-Benton).

A timeline compiled by the Sanders County Ledger from FWP records states that in 1917 much of eastern Montana was closed to deer hunting. I could not corroborate this in a second source. If accurate, it is notable, because eastern Montana is now where the state's mule deer are most numerous (Hagerman-Benton; Montana Fish, Wildlife and Parks, "2023 Mule Deer Population Report").

Systematic counting came later. FWP hired Robert F. Cooney as its first professional wildlife biologist in 1940, and in 1941 his crews surveyed game across eastern Montana county by county (Dickson 36-39). The same Ledger timeline reports that the statewide deer harvest reached 100,000 in 1955, another figure with a single source (Hagerman-Benton). The Montana Historical Society holds deer hunting regulations from the late 1950s onward in its Research Center Archives, but many are catalogued as unprocessed accessions, which limits their use by researchers (Montana Historical Society Research Center Archives).

Counting Deer, 2001 to 2017

In 2001 FWP adopted an adaptive harvest management plan for mule deer, tying hunting regulations to biological indicators of population trend. A FWP biologist reviewing the first nineteen years in Region 6, in northeastern Montana, reported that mule deer densities there rose significantly. Antlerless licenses in the region ranged from none in two separate years to more than 6,000 in 2019 as managers tried to hold numbers near average and limit conflicts with landowners (Williamson).

FWP's statewide model shows the same rise. Estimated mule deer numbers climbed from 232,268 in 2013 to 386,175 in 2017. The agency cautions that these figures come from modeling with survey and harvest inputs, carry no confidence intervals, and reflect a method changed in 2015 (Montana Fish, Wildlife and Parks, "2023 Mule Deer Population Report").

The Contraction

By 2023 the statewide estimate had fallen to 255,989, about a third below the 2017 peak and 17 percent below the ten-year average. The losses were uneven. Region 7 in southeastern Montana went from 135,000 in 2016 to 55,604 in 2023, or 41 percent below its average. Region 5 stood 20 percent below average and Region 4 stood 14 percent below. Regions 3 and 6 were slightly above average (Montana Fish, Wildlife and Parks, "2023 Mule Deer Population Report"; Eggert).

FWP attributes the southeastern drop mainly to drought. FWP wildlife manager Brett Dorak said that drought from 2020 through 2023 cut fawn recruitment there. A 2024 spring survey showed a 20 percent rebound in the region, still roughly 40 percent under the ten-year average (Desroches). FWP's disease report agrees that drought was the main driver and names bluetongue and epizootic hemorrhagic disease as lesser ones. It also records the licensing response: the Region 7 antlerless mule deer license quota fell from 11,000 in 2021 to 5,500 in 2022 and to 1,000 in 2023 and 2024 (McCormick et al.). In 2024 FWP also cut antlerless tags by about half in northeastern Montana (Desroches).

Chronic wasting disease, first detected in Montana's wild deer in 2017, is a separate concern. In the 2024-25 season FWP tested 9,504 animals, including 3,131 mule deer. Of 356 positives, 128 were mule deer, and the disease has now been found in 30 percent of hunting districts. Three-year prevalence among adult mule deer in positive districts ranged from under 1 percent to 23 percent, highest in districts 600, 640, and 670 in the northeast. Adult males carried about three times the infection risk of adult females (McCormick et al.). FWP notes that mule deer herds in Wyoming and Colorado declined at prevalences of 20 to 30 percent, but it does not attribute Montana's statewide decline to the disease (McCormick et al.).

Habitat research adds a further factor. A study of 136 GPS-collared mule deer in northwestern Montana, summarized by The Wildlife Society, found adult female survival near 79 percent against roughly 85 percent in a stable population. The researchers pointed to declining fire and logging disturbance, which once produced the young vegetation mule deer favor (The Wildlife Society). That finding rests on a single summary. FWP's Mule Deer Citizen Advisory Council, convened in 2024 as the agency began revising its management approach, listed habitat quality, hunting pressure, weather, and disease as possible contributors (Eggert).

What the Record Shows

The record supports three conclusions. Mule deer numbers have always moved in wide swings. Region 7 alone rose from 53,934 to 135,000 and back to 55,604 in a decade (Montana Fish, Wildlife and Parks, "2023 Mule Deer Population Report"). Systematic counting of the species is recent, and the modeled figures carry real uncertainty. And the causes of the current decline vary by region, with drought central in the southeast and disease and habitat more prominent elsewhere. Lewis's 1805 description, written on a windbound day on the Missouri, came two centuries before anyone measured these animals with any precision.

Works Cited

Desroches, Kayla. "Montana Mule Deer Population Continues Long-Term Decline, Hunting Tags to Be Limited." Yellowstone Public Radio, 28 June 2024, https://www.ypradio.org/wildlife-outdoors/2024-06-28/montana-mule-deer-population-continues-long-term-decline-hunting-tags-to-be-limited. Accessed 21 Oct. 2026.

Dickson, Tom. "FWP 125th Anniversary." Montana Outdoors, July-Aug. 2026, pp. 32-43, https://fwp.mt.gov/binaries/content/assets/fwp/montana-outdoors/2026/ja26/fwp-125th-anniversary.pdf. Accessed 21 Oct. 2026.

Eggert, Amanda. "FWP Solicits Public Comment on Mule Deer Management." Montana Free Press, 22 July 2024, https://montanafreepress.org/2024/07/22/montana-fwp-solicits-public-comment-on-mule-deer-management/. Accessed 21 Oct. 2026.

Hagerman-Benton, Sherry. "Remember When?" Sanders County Ledger, 18 Oct. 2018, https://www.scledger.net/story/2018/10/18/communities/remember-when/1959.html. Accessed 21 Oct. 2026.

Lewis, Meriwether. "May 10, 1805." The Journals of the Lewis and Clark Expedition, edited by Gary E. Moulton, U of Nebraska-Lincoln, https://lewisandclarkjournals.unl.edu/item/lc.jrn.1805-05-10. Accessed 21 Oct. 2026.

---. "May 18, 1805." Lewis and Clark Research Database, Terrain360 and Lewis and Clark Trust, https://lewisandclarkresearch.org/journal/lewis-may-18-1805/. Accessed 21 Oct. 2026.

McCormick, Bevin, et al. Montana Fish, Wildlife & Parks' 2024 Chronic Wasting Disease Surveillance and Monitoring Report. Montana Fish, Wildlife and Parks, 19 Aug. 2025, https://fwp.mt.gov/binaries/content/assets/fwp/conservation/cwd/2024-chronic-wasting-disease-annual-report_final.pdf. Accessed 21 Oct. 2026.

Montana Fish, Wildlife and Parks. 2023 Mule Deer Population Report. 13 Nov. 2023, https://fwp.mt.gov/binaries/content/assets/fwp/conservation/deer/2023-mt-mule-deer-estimates.pdf. Accessed 21 Oct. 2026.

Montana Historical Society Research Center Archives. "Montana. Department of Fish, Wildlife, and Parks." ArchivesSpace Public Interface, https://mhs.libraryhost.com/agents/corporate_entities/54. Accessed 21 Oct. 2026.

Tabish, Dillon. "An Age-Old Pursuit Renewed." Flathead Beacon, 1 Oct. 2015, https://flatheadbeacon.com/2015/10/01/an-age-old-pursuit-renewed/. Accessed 21 Oct. 2026.

The Wildlife Society. "JWM: For Montana Mule Deer, Is Migration Worth the Effort?" The Wildlife Society, n.d., https://wildlife.org/?p=54084. Accessed 21 Oct. 2026.

Williamson, Ryan M. "Looking Back at 19 Years of Mule Deer Adaptive Harvest Management in FWP Region 6." Intermountain Journal of Sciences, vol. 26, no. 1-4, Dec. 2020, https://arc.lib.montana.edu/ojs/index.php/IJS/article/view/3499. Accessed 21 Oct. 2026.