Yellowstone National Park

 

2,219,791 acres (899,015 hectares), the world's first national park (est. 1872), NW Wyo., extending into Montana and Idaho. It lies mainly on a broad plateau in the Rocky Mts., on the Continental Divide, c.8,000 ft (2,440 m) above sea level, surrounded by mountains from 10,000 to 14,000 ft (3,048–4,267 m) high. The area, a huge craterlike volcanic basin (caldera), is a geological “hot spot” and the site of several massive eruptions, the most recent occurring some 600,000 years ago. The plateau is mostly formed from once-molten lava.

Volcanic activity is evidenced by nearly 10,000 hot springs, 200 geysers, and many vents and mud pots. The more prominent geysers are unequaled in size, power, and variety. Old Faithful, the best known although not the largest, erupts every 40 to 70 min and shoots c.11,000 gal (41,640 liters) of water some 150 ft (46 m) high. Mammoth Hot Springs, a series of five terraces with reflecting pools, continues to grow as residue from the mineral-rich water is deposited.

The park also has petrified forests, lava formations, and the “black glass” Obsidian Cliff. Eagle Peak, 11,370 ft (3,466 m), is the highest point. Yellowstone Lake, the Grand Canyon of the Yellowstone, and waterfalls are notable features on the Yellowstone River, which crosses the park. The park has a wide variety of flowers and other plant life. Bears, mountain sheep, elk, bison, moose, many smaller animals, and more than 200 kinds of birds inhabit Yellowstone, which is one of the world's largest wildlife sanctuaries. Fires in 1988 burned about 36% of the park, but animal and plant life rebounded quickly, as the nutrient influx in the ash nourished the soil.

See also National Parks and Monuments, table.

Bibliography

See J. Muir, Yellowstone National Park (1979); B. T. Scott, The Geysers of Yellowstone (rev. ed. 1986); G. Wuerthner, Yellowstone & the Fires of Change (1988).

Yellowstone National Park
IUCN Category II (National Park)
Location	Wyoming, Montana and Idaho, U.S.
Coordinates	44°36′0″N 110°30′0″W / 44.6, -110.5
Area	2,219,789 acres (8,983 km²)[1]
Established	March 1, 1872
Total visitation	2,870,295[2] (in 2006)
Governing body	National Park Service
World Heritage Site	September 8, 1978

Yellowstone National Park became the world's first national park on March 1, 1872.^[1] Located mostly in the U.S. state of Wyoming, the park extends into Montana and Idaho. The park is known for its wildlife and geothermal features, especially Old Faithful Geyser, one of the most popular areas in the park.

Native Americans have lived in the Yellowstone region for at least 11,000 years. The region was bypassed during the Lewis and Clark Expedition in the early 1800s. Aside from visits by mountain men during the early to mid-1800s, organized exploration did not begin until the late 1860s. The U.S. Army was commissioned to oversee the park just after its establishment. In 1917, administration of the park was transferred to the National Park Service, which had been created the previous year. Hundreds of structures have been built and are protected for their architectural and historical significance, and researchers have examined more than 1,000 archaeological sites.

Yellowstone National Park spans an area of 3,472 square miles (8,987 km²), comprising lakes, canyons, rivers and mountain ranges.^[1] Yellowstone Lake is the largest high-altitude lake in North America and is centered over the Yellowstone Caldera, the largest supervolcano on the continent. The caldera is considered an active volcano; it has erupted with tremendous force several times in the last two million years. Half of the world's geothermal features are in Yellowstone, fueled by this ongoing volcanism.^[3] Lava flows and rocks from volcanic eruptions cover most of the land area of Yellowstone. The park is the centerpiece of the Greater Yellowstone Ecosystem, the largest remaining, nearly-intact ecosystem in the Earth's northern temperate zone.^[4]

Hundreds of species of mammals, birds, fish and reptiles have been documented, including several that are either endangered or threatened.^[1] The vast forests and grasslands also include unique species of plants. Grizzlies, wolves, and free-ranging herds of bison and elk live in the park. Forest fires occur in the park each year; in the large forest fires of 1988, nearly one third of the park burned. Yellowstone has numerous recreational opportunities, including hiking, camping, boating, fishing and sightseeing. Paved roads provide close access to the major geothermal areas as well as some of the lakes and waterfalls. During the winter, visitors often access the park by way of guided tours that use either snow coaches or snowmobile.

Early history

The park is located at the headwaters of the Yellowstone River, from which it takes its name. In the eighteenth century, French Trappers named the river "Roche Jaune," which is probably a translation of the Minnetaree name "Mi tsi a-da-zi" (Rock Yellow River). Later, American trappers rendered the French name in English as "Yellow Stone." Although it is commonly believed that the river was named for the yellow rocks seen in the Grand Canyon of the Yellowstone, the Native American name source is not clear.^[5]

The human history of the park begins at least 11,000 years ago when Native Americans first began to hunt and fish in the region. During the construction of the post office in Gardiner, Montana, in the 1950s, an obsidian projectile point of Clovis origin was found that dated from approximately 11,000 years ago.^[6] These Paleo-indians, of the Clovis culture, used the significant amounts of obsidian found in the park to make such cutting tools and weapons. Arrowheads made of Yellowstone obsidian have been found as far away as the Mississippi Valley, indicating that a regular obsidian trade existed between local tribes and tribes farther east.^[7] By the time white explorers first entered the region during the Lewis and Clark Expedition in 1805, they encountered the Nez Perce, Crow and Shoshone tribes. While passing through present day Montana, the expedition members were informed of the Yellowstone region to the south, but they did not investigate it.^[7]

In 1806, John Colter, a member of the Lewis and Clark Expedition, left to join a group of fur trappers. After splitting up with the other trappers in 1807, Colter passed through a portion of what later became the park, during the winter of 1807–1808. He observed at least one geothermal area in the northeastern section of the park, near Tower Falls.^[8] After surviving wounds he suffered in a battle with members of the Crow and Blackfoot tribes in 1809, he gave a description of a place of "fire and brimstone" that was dismissed by most people as delirium. The supposedly imaginary place was nicknamed "Colter's Hell." Over the next forty years, numerous reports from mountain men and trappers told of boiling mud, steaming rivers and petrified trees, yet most of these reports were believed at the time to be myth.^[9]

After an 1856 exploration, mountain man Jim Bridger reported observing boiling springs, spouting water, and a mountain of glass and yellow rock. These reports were largely ignored because Bridger was known for being a "spinner of yarns". His stories did arouse the interest of explorer and geologist Ferdinand Vandeveer Hayden, who, in 1859, started a two-year survey of the upper Missouri River region. Bridger and United States Army surveyor W.F. Raynolds acted as guides. After exploring the Black Hills region in what is now the state of South Dakota, the party neared the Yellowstone River, but heavy snows forced them to turn back. The American Civil War hampered further organized explorations until the late 1860s.^[10]

The first detailed expedition to the Yellowstone area was the Folsom Expedition of 1869, which consisted of three privately funded explorers. The Folsom party followed the Yellowstone River to Yellowstone Lake.^[11] The members of the Folsom party kept a journal and based on the information it reported, a party of Montana residents organized the Washburn-Langford-Doane Expedition in 1870. It was headed by the surveyor-general of Montana Henry Washburn, and included Nathaniel P. Langford (who later became known as "National Park" Langford) and a U.S. Army detachment commanded by Lt. Gustavus Doane. The expedition spent about a month exploring the region, collecting specimens, and naming sites of interest. A Montana writer and lawyer named Cornelius Hedges, who had been a member of the Washburn expedition, proposed that the region should be set aside and protected as a National Park; he wrote numerous detailed articles about his observations for the Helena Herald newspaper between 1870 and 1871. Hedges essentially restated comments made in October 1865 by acting Montana Territorial Governor Thomas Francis Meagher, who had previously commented that the region should be protected.^[12] Others made similar suggestions. In a 1871 letter from Jay Cooke to Ferdinand Hayden, Cooke wrote that his friend, Senator William D. Kelley had also suggested "Congress pass a bill reserving the Great Geyser Basin as a public park forever".^[13]

Park creation and later history

In 1871, eleven years after his failed first effort, F.V. Hayden was finally able to make another attempt to explore the region. With government sponsorship, Hayden returned to Yellowstone with a second, larger expedition. He compiled a comprehensive report on Yellowstone, which included large-format photographs by William Henry Jackson, as well as paintings by Thomas Moran. His report helped to convince the U.S. Congress to withdraw this region from public auction; on March 1, 1872, President Ulysses S. Grant signed a bill into law that created Yellowstone National Park.^[14]

Nathaniel Langford was appointed as the park's first superintendent in 1872. He served for five years but was denied a salary, funding, and staff. Langford lacked the means to improve the land or properly protect the park, and without formal policy or regulations, he had few legal methods to enforce such protection. This left Yellowstone vulnerable to poachers, vandals, and others seeking to raid its resources. As a result, Langford was forced to step down in 1877.^[15][16] Having traveled through Yellowstone and witnessed land management problems first hand, Philetus Norris volunteered for the position following Langford's exit. Congress finally saw fit to implement a salary for the position, as well as to provide a minimal funding to operate the park. Norris used these funds to expand access to the park, building numerous crude roads and facilities.^[16] Norris hired Harry Yount to control poaching and vandalism in the park. Today, Harry Yount is considered the first national park ranger.^[17] However, these measures still proved to be insufficient in protecting the park, as neither Norris, nor the three superintendents who followed, were given sufficient manpower or resources.

The Northern Pacific Railroad built a train station in Livingston, Montana, connecting to the northern entrance in the early 1880s, which helped to increase visitation from 300 in 1872 to 5,000 in 1883.^[18] Visitors in these early years were faced with poor roads and limited services, and most access into the park was on horse or via stagecoach. By 1908 visitation increased enough to also attract a Union Pacific Railroad connection to West Yellowstone, though rail visitation fell off considerably by World War II and ceased around the 1960s.

Ongoing poaching and destruction of natural resources continued unabated until the U.S. Army arrived at Mammoth Hot Springs in 1886 and built Camp Sheridan. Over the next 22 years the army constructed permanent structures, and Camp Sheridan was renamed Fort Yellowstone.^[19] With the funding and manpower necessary to keep a diligent watch, the army developed their own policies and regulations that permitted public access while protecting park wildlife and natural resources. When the National Park Service was created in 1916, many of the management principles developed by the army were adopted by the new agency.^[19] The army turned control over to the National Park Service on October 31, 1918.^[20]

By 1915, 1,000 automobiles per year were entering the park, resulting in conflicts with horses and horse driven transportation. In subsequent years horse travel on roads was eventually prohibited.^[21] Between 1933 and 1941, the Civilian Conservation Corps built the majority of the early visitor centers, campgrounds and the current system of park roads. During World War II, staffing and visitation both decreased, and many facilities fell into disrepair.^[22] By the 1950s, visitation increased tremendously in Yellowstone and other national parks. To accommodate the increased visitation, park officials implemented Mission 66, an effort to modernize and expand park service facilities. Planned to be completed by 1966, in honor of the 50th anniversary of the founding of the National Park Service, Mission 66 construction diverged from the traditional log cabin style with design features of a modern style.^[23] During the late 1980s, most construction styles in Yellowstone reverted back to the more traditional designs. After the enormous forest fires of 1988 damaged much of Grant Village, structures there were rebuilt in the traditional style. The visitor center at Canyon Village, which opened in 2006, incorporates a more traditional design as well.^[24]

In 1959, a powerful earthquake just west of Yellowstone at Hebgen Lake damaged roads and some structures in the park. In the northwest section of the park, new geysers were found, and many existing hot springs became turbid.^[25]

The wildfires during the summer of 1988 were the largest in the history of the park. Approximately 793,880 acres (3,213 km²) or 36% of the parkland was impacted by the fires, leading to a systematic reevaluation of fire management policies. The fire season of 1988 was considered normal until a combination of drought and heat by mid-July contributed to an extreme fire danger. On "Black Saturday," August 20, 1988, strong winds expanded the fires rapidly, and more than 150,000 acres (610 km²) were consumed.^[26]

The expansive cultural history of the park has been documented by the 1,000 archeological sites that have been discovered. The park has 1,106 historic structures and features, and of these Obsidian Cliff and five buildings have been designated National Historic Landmarks.^[1] Yellowstone was designated an International Biosphere Reserve on October 26, 1976, and a United Nations World Heritage Site on September 8, 1978.

Geography

Approximately 96% of the land area of Yellowstone National Park is located within the state of Wyoming. Another 3% is within Montana, with the remaining 1% in Idaho. The park is 63 miles (102 km) north to south, and 54 miles (87 km) west to east by air. At 2,219,789 acres (8,983 km²), Yellowstone is larger than the states of Rhode Island and Delaware combined. Rivers and lakes cover 5% of the land area, with the largest water body being Yellowstone Lake at 87,040 acres (352.2 km²). Yellowstone Lake is up to 400 feet (122 m) deep and has 110 miles (177 km) of shoreline. Sitting at an elevation of 7,733 feet (2,357 m) above sea level, Yellowstone Lake is the largest high altitude lake in North America. Forests comprise 80% of the land area of the park; most of the rest is grassland.^[1]

The Continental Divide of North America runs diagonally through the southwestern part of the park. The divide is a topographic feature that separates Pacific Ocean and Atlantic Ocean water drainages. About one third of the park lies on the west side of the divide. The origins of the Yellowstone and Snake Rivers are near each other but on opposite sides of the divide. As a result, the waters of the Snake River flow to the Pacific Ocean, while those of the Yellowstone find their way to the Atlantic Ocean via the Gulf of Mexico.

The park sits on the Yellowstone Plateau, at an average altitude of 8,000 feet (2,400 m) above sea level. The plateau is bounded on nearly all sides by mountain ranges of the Middle Rocky Mountains, which range from 9,000 to 11,000 feet (2,743 to 3,352 m) in elevation. The highest point in the park is atop Eagle Peak (11,358 ft/3,462 m) and the lowest is along Reese Creek (5,282 ft/1,610 m).^[1] Nearby mountain ranges include the Gallatin Range to the northwest, the Beartooth Mountains in the north, the Absaroka Range to the east, and the Teton Range and the Madison Range to the southwest and west. The most prominent summit on the Yellowstone Plateau is Mount Washburn at 10,243 feet (3,122 m).

Yellowstone National Park has one of the world's largest petrified forests, trees which were long ago buried by ash and soil and transformed from wood to mineral materials. There are 290 waterfalls of at least 15 feet (4.5 m) in the park, the highest being the Lower Falls of the Yellowstone River at 308 feet (94 m).^[1]

Two deep canyons are located in the park, cut through the volcanic tuff of the Yellowstone Plateau by rivers over the last 640,000 years. The Lewis River flows through Lewis Canyon in the south, and the Yellowstone River has carved the colorful Grand Canyon of the Yellowstone in its journey north.

Geology

Main articles: Geothermal areas of Yellowstone, Yellowstone Caldera, and Supervolcano

Yellowstone is at the northeastern end of the Snake River Plain, a great U-shaped arc through the mountains that extends from Boise, Idaho some  mi ( km) to the west. This feature traces the route over the last 17 million years of the North American Plate as it was transported by plate tectonics across a stationary mantle hotspot. The landscape of present-day Yellowstone National Park is but the most recent manifestation of this hotspot below the crust of the Earth.^[27]

The Yellowstone Caldera is the largest volcanic system in North America. It has been termed a "supervolcano" because the caldera was formed by exceptionally large explosive eruptions. The current caldera was created by a cataclysmic eruption that occurred 640,000 years ago, which released 240 cubic miles (1,000 km³) of ash, rock and pyroclastic materials. This eruption was 1,000 times larger than the 1980 eruption of Mount St. Helens.^[28] It produced a crater nearly a two thirds of a mile (1 km) deep and 52 by 28 miles (85 by 45 km) in area and deposited the Lava Creek Tuff, a welded tuff geologic formation. The most violent known eruption, which occurred 2.1 million years ago, ejected 588 cubic miles (2,450 km³) of volcanic material and created the rock formation known as the Huckleberry Ridge Tuff.^[29] A smaller eruption ejected 67 cubic miles (280 km³) of material 1.2 million years ago, forming the Island Park Caldera and depositing the Mesa Falls Tuff.^[28]

Each of the three climax eruptions released vast amounts of ash that blanketed much of central North America falling many hundreds of miles away. The amount of ash and gases released into the atmosphere probably caused significant impacts to world weather patterns and led to the extinction of many species, primarily in North America.^[30]

A subsequent minor climax eruption occurred 160,000 years ago. It formed the relatively small caldera that contains the West Thumb of Yellowstone Lake. Later, two smaller eruptive cycles, the last one ending about 70,000 years ago, buried much of the caldera under thick lava flows.^[29]

Each eruption is in fact a part of an eruptive cycle that climaxes with the collapse of the roof of a partially emptied magma chamber. This creates a crater, called a caldera, and releases vast amounts of volcanic material, usually through fissures that ring the caldera. The time between the last three cataclysmic eruptions in the Yellowstone area has ranged from 600,000 to 900,000 years, but the small number of such climax eruptions cannot be used to make a prediction for future volcanic events.^[31]

Between 630,000 and 700,000 years ago, Yellowstone Caldera was nearly filled in with periodic eruptions of rhyolitic lavas such as those that can be seen at Obsidian Cliffs and basaltic lavas which can be viewed at Sheepeaters Cliff. Lava strata are most easily seen at the Grand Canyon of the Yellowstone, where the Yellowstone River continues to carve into the ancient lava flows. The canyon is a classic V-shaped valley, indicative of river-type erosion rather than erosion caused by glaciation.

The most famous geyser in the park, and perhaps the world, is Old Faithful Geyser, located in Upper Geyser Basin; the park also contains the largest active geyser in the world—Steamboat Geyser in the Norris Geyser Basin. There are 300 geysers in Yellowstone and a total of at least 10,000 geothermal features altogether. Half the geothermal features and two-thirds of the world's geysers are concentrated in Yellowstone.^[32]

In May 2001, the U.S. Geological Survey, Yellowstone National Park, and the University of Utah created the Yellowstone Volcano Observatory (YVO), a partnership for long-term monitoring of the geological processes of the Yellowstone Plateau volcanic field, for disseminating information concerning the potential hazards of this geologically active region.^[33]

In 2003, changes at the Norris Geyser Basin resulted in the temporary closure of some trails in the basin. New fumaroles were observed, and several geysers showed enhanced activity and increasing water temperatures. Several geysers became so hot that they were transformed into purely steaming features; the water had become superheated and they could no longer erupt normally.^[34] This coincided with the release of reports of a multiple year United States Geological Survey research project which mapped the bottom of Yellowstone Lake and identified a structural dome that had uplifted at some time in the past. Research indicated that these uplifts posed no immediate threat of a volcanic eruption, since they may have developed long ago, and there had been no temperature increase found near the uplifts.^[35] On March 10, 2004, a biologist discovered 5 dead bison which apparently had inhaled toxic geothermal gases trapped in the Norris Geyser Basin by a seasonal atmospheric inversion. This was closely followed by an upsurge of earthquake activity in April 2004.^[36] In 2006, it was reported that the Mallard Lake Dome and the Sour Creek Dome— areas that have long been known to show significant changes in their ground movement— had risen at a rate of 1.5 to 2.4 inches (4 to 6 cm) per year since 2004.^[37] These events inspired a great deal of media attention and speculation about the geologic future of the region. Experts responded to the conjecture by informing the public that there was no increased risk of a volcanic eruption in the near future.^[38]

Yellowstone experiences thousands of small earthquakes every year, virtually all of which are undetectable to people. There have been six earthquakes with at least magnitude 6 or greater in historical times, including a 7.5 magnitude quake that struck just outside the northwest boundary of the park in 1959. This quake triggered a huge landslide, which caused a partial dam collapse on Hebgen Lake; immediately downstream, the sediment from the landslide dammed the river and created a new lake, known as Earthquake Lake. Twenty-eight people were killed, and property damage was extensive in the immediate region. The earthquake caused some geysers in the northwestern section of the park to erupt, large cracks in the ground formed and emitted steam, and some hot springs' normally clear water turned muddy.^[25] A 6.1 magnitude earthquake struck inside the park on June 30 1975, but damage was minimal. For three months in 1985, 3,000 minor earthquakes were detected in the northwestern section of the park, during what has been referred to as an earthquake swarm, and has been attributed to minor subsidence of the Yellowstone caldera.^[28] Beginning on April 30, 2007, sixteen small earthquakes with magnitudes up to 2.7 occurred in the Yellowstone Caldera for several days. These swarms of earthquakes are common, and there have been 70 such swarms between 1983 and 2006.^[39]

Biology and ecology

Main article: Greater Yellowstone Ecosystem

Yellowstone National Park is the centerpiece of the 20 million acre/31,250 mi² (8,093,712 ha/80,937 km²) Greater Yellowstone Ecosystem, a region that includes Grand Teton National Park, adjacent National Forests and expansive wilderness areas in those forests. The ecosystem is the largest remaining continuous stretch of mostly undeveloped pristine land in the United States outside of Alaska and is considered to be the world's largest intact ecosystem in the northern temperate zone.^[4] With the successful wolf reintroduction program, which began in the 1990s, virtually all the original faunal species known to inhabit the region when white explorers first entered the area can still be found there.

Flora

1,700 species of trees, plants, lichens and other vascular plants are native to the park. Another 170 species are considered to be exotic species and are non-native. Of the eight conifer tree species documented, Lodgepole pine forests cover 80% of the total forested areas.^[1] Other conifers, such as the douglas fir and whitebark pine, are found in scattered groves throughout the park. As of 2007, the whitebark pine is threatened by a fungus known as white pine blister rust; however, this is mostly confined to forests well to the north and west. In Yellowstone, about seven percent of the whitebark pine species have been impacted with the fungus, compared to nearly complete infestations in northwestern Montana.^[40] Aspen and willow are the most common species of deciduous trees. The aspen forests have declined significantly since the early 20th century, but scientists at Oregon State University attribute recent recovery of the aspen to the reintroduction of wolves which has changed the grazing habits of local elk.^[41]

There are dozens of species of flowering plants that have been identified, most of which bloom between the months of May and September.^[42] The Yellowstone Sand Verbena is a rare flowering plant found only in Yellowstone. It is closely related to species usually found in much warmer climates, making the sand verbena an enigma. The estimated 8,000 examples of this rare flowering plant all make their home in the sandy soils on the shores of Yellowstone Lake, well above the waterline.^[43]

In Yellowstone's hot waters, bacteria form mats of bizarre shapes consisting of trillions of individuals. These bacteria are some of the most primitive lifeforms on earth. Flies and other arthropods live on the mats, even in the middle of the bitterly cold winters. Initially, scientists thought that microbes there gained sustenance only from sulfur. In 2005, researchers from the University of Colorado at Boulder discovered that the sustenance for at least some of the diverse hyperthermophilic species is molecular hydrogen.^[44]

Thermus aquaticus is a bacteria found in the Yellowstone hot springs produces an important enzyme that is easily replicated in the lab and is useful in diagnosing hereditary and infectious diseases, as well as identification of genetic fingerprints. The retrieval of these bacteria can be achieved with no impact to the ecosystem. Other bacteria in the Yellowstone hot springs may also prove useful to scientists who are searching for cures for various diseases.^[45]

Non-native plants sometimes threaten native species by using up nutrient resources. Though exotic species are most commonly found in areas with the greatest human visitation, such as near roads and at major tourist areas, they have also spread into the backcountry. Generally, most exotic species are controlled by pulling the plants out of the soil or by spraying, both of which are time consuming and expensive.^[46]

Fauna

Main articles: Animals of Yellowstone and Wolf reintroduction

Yellowstone is widely considered to be the finest megafauna wildlife habitat in the lower 48 states. There are almost 60 species of mammals in the park, including the endangered gray wolf, the threatened lynx, and grizzly bears.^[1] Other large mammals include the bison (buffalo), black bear, elk, moose, mule deer, mountain goat, pronghorn, bighorn sheep and mountain lion.

The relatively large bison populations are a concern for ranchers, who fear that the species can transmit bovine diseases to their domesticated cousins. In fact, about half of Yellowstone's bison have been exposed to brucellosis, a bacterial disease that came to North America with European cattle that may cause cattle to miscarry. The disease has little effect on park bison, and no reported case of transmission from wild bison to domestic livestock has been filed. However, the Animal and Plant Health Inspection Service (APHIS) has stated that Bison are the "likely source" of the spread of the disease in cattle in Wyoming and North Dakota. Elk also carry the disease and are believed to have transmitted the infection to horses and cattle.^[47] Bison once numbered between 30 and 60 million individuals throughout North America, and Yellowstone remains one of their last strongholds. Their populations had increased from less than 50 in the park in 1902 to 4,000 by 2003.^[48]

To combat the perceived threat, national park personnel regularly harass bison herds back into the park when they venture outside of the area's borders. During the winter of 1996–97, the bison herd was so large that 1,079 bison that had exited the park were shot or sent to slaughter.^[47] Animal rights activists argue that this is a cruel practice and that the possibility for disease transmission is not as great as some ranchers maintain. Ecologists point out that the bison are merely traveling to seasonal grazing areas that lie within the Greater Yellowstone Ecosystem that have been converted to cattle grazing, some of which are within National Forests and are leased to private ranchers. APHIS has stated that with vaccinations and other means, brucellosis can be eliminated from the bison and elk herds throughout Yellowstone.^[47]

After the wolves were extirpated from Yellowstone, the coyote then became the park's top canine predator. However, the coyote is not able to bring down large animals, and the result of this lack of a top predator on these populations was a marked increase in lame and sick megafauna. Starting in 1914, in an effort to protect elk populations, the U.S. Congress appropriated funds to be used for the purposes of "destroying wolves, prairie dogs, and other animals injurious to agriculture and animal husbandry" on public lands. Park Service hunters carried out these orders, and by 1926 they had killed 136 wolves, and wolves were virtually eliminated from Yellowstone.^[49] Further exterminations continued until the National Park Service ended the practice in 1935. With the passing of the Endangered Species Act in 1973, the wolf was one of the first mammal species listed.^[49]

By the 1990s, the Federal government had reversed its views on wolves. In a controversial decision by the U.S. Fish and Wildlife Service (which oversees threatened and endangered species), Mackenzie Valley wolves, imported from Canada, were reintroduced into the park. Reintroduction efforts have been successful with populations remaining relatively stable. A survey conducted in 2005 reported that there were 13 wolf packs, totaling 118 individuals in Yellowstone and 326 in the entire ecosystem. These park figures were lower than those reported in 2004 but may be attributable to wolf migration to other nearby areas as suggested by the substantial increase in the Montana population during that interval.^[50] Almost all the wolves documented were descended from the 66 wolves reintroduced in 1995–96.^[50] The recovery of populations throughout the states of Wyoming, Montana and Idaho has been so successful that the U.S. Fish and Wildlife Service has proposed delisting the wolf as a threatened and endangered species.^[51]

An estimated 600 grizzly bears live in the Greater Yellowstone Ecosystem, with more than half of the population living within Yellowstone. The grizzly is currently listed as a threatened species, however the U.S. Fish and Wildlife Service has announced that they intend to take it off the endangered species list for the Yellowstone region but will likely keep it listed in areas where it has not yet recovered fully. Opponents of delisting the grizzly are concerned that states might once again allow hunting and that better conservation measures need to be implemented to ensure a sustainable population.