By the early 1920s, overgrazing was beginning to result in reduced livestock production. This spurred the development of better grazing management systems that proved instrumental in providing more usable habitat for mule deer, particularly on National Forests. In various parts of the West, grazing capacity for livestock in the early 1930's was estimated to be 60 to 90 percent less than in pioneer days9. By 1960, sheep numbers had fallen to about 2.5 million from from about 8 million in 1918.5 Much of the reduction in livestock use was due to the Taylor Grazing Service which was created in 1934 to better manage grazing impacts on public lands. During this period, state wildlife management agencies were also beginning to actively engage in the management of big game species and habitats. In 1934, Cooperative Wildlife Research Units were initiated at universities across the nation to conduct wildlife research and provide academic training in professional wildlife management. Meanwhile, populations of "vermin" like mountain lions, wolves, bobcats, lynx, and coyotes continued to be suppressed by government-funded predator control programs.
The 1930s might also be considered the dawn of the era of modern wildlife management. In 1937, President Franklin D. Roosevelt signed the Pittman-Robertson Federal Aid in Wildlife Restoration Act, providing funding which Colorado first used to undertake research on nutritional requirements of the Sapinero deer herd and Gunnison elk herd.
By the mid-1930s, statewide estimates placed the number of elk at 27,000 and deer at between 50,000 and 60,000, numbers that were beginning to compromise the quality of winter range. Colorado's first aerial big game counts were flown in 1938 to provide better data for big game managers. In 1939 the Game and Fish Commission was granted authority to open seasons on female deer and elk which had been closed for over thirty years. In 1940, surveys of both mule deer numbers and deer habitat were conducted in the Gunnison Basin of southwestern Colorado. The basin's mule deer population was estimated at approximately 22,000 deer while carrying capacity was estimated at approximately 12,000 deer.
In 1937 Congress authorizes the Colorado Big Thompson Project to bring water from the headwaters of the Colorado river to the South Platte drainage on the eastern slope.
However, several weather events during this period reminded wildlife managers about the vulnerability of mule deer to environmental extremes. Colorado experienced severe drought during the 'dust bowl' years of the 1930's, which limited browse availability for deer. A heavy winter in 1935-1936 spurred the Game and Fish Department to feed more than 15,000 animals in the Gunnison basin. In January 1941, more than 1,600 deer died of malnutrition from insufficient browse on overgrazed range. The resurgent elk population convinced the Department to offer the first limited licenses for a late-season elk hunt. By the end of the winter of 1942 the Department disposed of 5,266 deer that had died on the Gunnison feeding grounds. The winter of 1948-1949 was so harsh that artificial feeding, abandoned after the winter of 1941-1942, was reinstated.
Nevertheless, by the 1940s and 1950s, wildlife managers found themselves dealing with tens of thousands of game animals in a region where just a half-century earlier, there were too few to hunt. Mounting agricultural damage complaints and increasing demand for recreational and subsistence hunting opportunity during the war ushered in an era of liberal harvest management. During this period, wildlife managers regularly extended hunting seasons. In certain areas, a hunter could take two deer on a license.
The early 1940s saw the harvest of the last gray wolf in the state.
In 1945, resident hunters enjoyed their first pronghorn season in more than four decades.
From the 1940's to the 1950's, the "Uranium boom" created significant mining activity in the Paradox valley southwest of Montrose to feed the wartime mills in Grand Junction and Rifle. This exposed the Uncompahgre Plateau's deer herds to a rapid increase in hunting pressure. In the 1950's, the White River deer herd was estimated to be over 50,000 deer. In 1951 two deer of either sex were allowed per license. By 1953, in certain areas, hunters could buy unlimited licenses and take a deer on each license. The abundance of game and liberal hunting regulations produced large game harvests by the late 1950s, with 114,529 deer taken in 1957 and 10,820 elk harvested in 1958.
The science of wildlife management also saw significant advances during the 1940s.
In 1945, the state Legislature granted the Wildlife Commission the authority to buy and sell lands and water. The Little Hills big game research station, which would become one of the premier wildlife research stations in the country, was purchased the following year. With its 15,000 acres of prime Piceance Basin winter range, Little Hills was large enough to allow researchers to apply range analysis techniques, originally developed for livestock, to deer and elk.
The mid-1940s also marked the first effort by the Department to collect information from hunters, via a postcard attached to big game licenses. Meanwhile in 1957, the state introduced the game management unit concept in the area west of the Continental Divide, the first application of what would become the basis for Colorado's herd management system.
The recovery of deer and elk in Colorado from the 1930's to the 1950's reflected a trend across the West. Population surveys showed that deer and elk numbers during this period were greater than at any previous time in the 20th century. For example, mule deer were scarce in Jackson Hole, Wyo. prior to 1930 but common by 1950.9 In Nevada, the Ruby Mountain deer herd expanded to between 25,000 and 30,000 animals by the mid-1950s, according to the state fish and game department. In Utah, the mule deer population jumped more than 40-fold from an estimated 8,500 in 1916 to 375,000 between 1945 and 1950. Idaho officials estimated that their deer population (including white-tailed deer) increased from 45,000 in 1923-24 to 315,000 in 1963.3
Numerous wildlife and range studies 3,10,11 including a general synopsis12 published in 1986 and endorsed by the Western Association of Fish and Wildlife Agencies, concluded that a major reason mule deer populations expanded so dramatically by the 1950s was that human activity promoted a widespread shift from bunchgrass-dominated vegetation to early- and mid-successional stages of sagebrush and other shrubs. These changes in plant community composition favored mule deer.