Editing Yellowstone National Park (section)

== Biology and ecology ==
{{Main|Greater Yellowstone Ecosystem|Ecology of the Rocky Mountains}}
[[File:Beautiful Meadow in Yellowstone National Park.JPG|thumb|Meadow in Yellowstone National Park]]
Yellowstone National Park is the centerpiece of the {{convert|20|e6acre|km2 mi2|sigfig=4}} Greater Yellowstone Ecosystem, a region that includes [[Grand Teton National Park]], adjacent [[United States National Forest|National Forests]] and expansive [[wilderness]] areas in those forests. The ecosystem is the largest remaining continuous stretch of mostly undeveloped pristine land in the contiguous United States, considered the world's largest intact ecosystem in the northern temperate zone.<ref name="ecosystem" /> With the successful [[wolf reintroduction]] program, which began in the 1990s, much of the original faunal and floral species known to inhabit the region when the first explorers entered the area can be found there.<ref>{{Cite web |last=Rappaport Clark |first=Jamie |date=March 21, 2020 |title=We Were Wrong About Wolves, Here's Why |url=https://defenders.org/blog/2020/03/we-were-wrong-about-wolves-heres-why#:~:text=Wolf%20reintroduction%20caused%20unanticipated%20change,%2C%20eagles%2C%20foxes%20and%20badgers. |access-date=June 7, 2023 |website=Defenders of Wildlife |archive-date=June 8, 2023 |archive-url=https://web.archive.org/web/20230608224227/https://defenders.org/blog/2020/03/we-were-wrong-about-wolves-heres-why#:~:text=Wolf%20reintroduction%20caused%20unanticipated%20change,%2C%20eagles%2C%20foxes%20and%20badgers. |url-status=live }}</ref><ref>{{Cite web |last=Farquhar |first=Brodie |date=June 30, 2021 |title=Wolf Reintroduction Changes Ecosystem in Yellowstone |url=https://www.yellowstonepark.com/things-to-do/wildlife/wolf-reintroduction-changes-ecosystem/ |access-date=June 7, 2023 |website=yellowstonepark.com |archive-date=June 9, 2023 |archive-url=https://web.archive.org/web/20230609064737/https://www.yellowstonepark.com/things-to-do/wildlife/wolf-reintroduction-changes-ecosystem/ |url-status=live }}</ref> The site is home to a key field observation site for the [[National Ecological Observatory Network]].<ref name="NSF NEON 2020">{{cite web |title=Yellowstone National Park NEON — Open Data to Understand our Ecosystems |website=NSF NEON |date=April 30, 2020 |url=https://www.neonscience.org/field-sites/yell |access-date=October 16, 2023 |archive-date=October 22, 2023 |archive-url=https://web.archive.org/web/20231022224404/https://www.neonscience.org/field-sites/yell |url-status=live }}</ref>

=== Flora ===
Over 69,000 [[species]] of trees and other [[vascular plant]]s 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.<ref name="facts"/> Other conifers, such as [[subalpine fir]], [[Engelmann spruce]], [[Rocky Mountain Douglas-fir]] and [[whitebark pine]], are found in scattered groves throughout the park. As of 2007,{{update after|2021|3|4}} the whitebark pine is threatened by a fungus known as [[Cronartium ribicola|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.<ref name="whitebark">{{cite web |last=Kendall |first=Katherine |url=http://biology.usgs.gov/s+t/SNT/noframe/wm147.htm |title=Whitebark Pine |website=Our Living Resources |publisher=U.S. Geological Survey |access-date=March 13, 2007 |archive-url=https://web.archive.org/web/20060927145101/http://biology.usgs.gov/s%2Bt/SNT/noframe/wm147.htm |archive-date=September 27, 2006 |url-status=dead }}</ref> [[Quaking Aspen]] and [[willow]]s 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 the recent recovery of the aspen to the [[History of wolves in Yellowstone|reintroduction of wolves]] which has changed the grazing habits of local elk.<ref name="aspen">{{cite web |title=Presence Of Wolves Allows Aspen Recovery in Yellowstone |url=https://www.sciencedaily.com/releases/2007/07/070726150904.htm |access-date=August 1, 2007 |url-status=live |archive-url=https://web.archive.org/web/20071001001225/https://www.sciencedaily.com/releases/2007/07/070726150904.htm |archive-date=October 1, 2007 }}</ref>
[[File:Abronia ammophila.jpg|thumb|[[Abronia ammophila|Yellowstone sand verbena]] is endemic to Yellowstone's lakeshores]]

There are dozens of species of flowering plants that have been identified, most of which bloom between May and September.<ref name="flowers">{{cite web |url=http://www.nps.gov/yell/naturescience/upload/286wildflowers.pdf |title=Where Are the Bloomin' Wildflowers? |publisher=National Park Service |date=February 2004 |access-date=March 13, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070616094322/http://www.nps.gov/yell/naturescience/upload/286wildflowers.pdf |archive-date=June 16, 2007 }}</ref> The [[Abronia ammophila|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.<ref name="verbena">{{cite web |url=http://www.nps.gov/yell/naturescience/verbena.htm |title=Yellowstone Sand Verbena |website=Nature and Science |publisher=National Park Service |date=July 20, 2006 |access-date=March 13, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070607165823/http://www.nps.gov/yell/naturescience/verbena.htm |archive-date=June 7, 2007 }}</ref>
[[File:Microbes, Yellowstone National Park.jpg|thumb|Microbial mat in cooled geyser water, Upper Geyser Basin]]
In Yellowstone's hot waters, bacteria form mats of bizarre shapes consisting of trillions of organisms. These bacteria are some of the most primitive life forms on earth. Flies and other [[arthropod]]s 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 [[Hyperthermophile|hyperthermophilic]] species is [[hydrogen|molecular hydrogen]].<ref name="bacteria">{{cite web |url=http://www.colorado.edu/news/releases/2005/30.html |title=Microbes in Colorful Yellowstone Hot Springs Fueled By Hydrogen, CU-Boulder Researchers Say |publisher=University of Colorado at Boulder |date=January 24, 2005 |access-date=March 13, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20130426150324/http://www.colorado.edu/news/releases/2005/30.html |archive-date=April 26, 2013 }}</ref>

''[[Thermus aquaticus]]'' is a [[Bacteria|bacterium]] found in the Yellowstone hot springs that produces an important enzyme (Taq polymerase) that is easily replicated in the lab and is useful in replicating [[DNA]] as part of the [[polymerase chain reaction]] (PCR) process. The retrieval of these bacteria can be achieved with no impact on the ecosystem. Other bacteria in the Yellowstone hot springs may also prove useful to scientists who are searching for cures for various diseases.<ref>{{cite web |title=The Yellowstone Thermophiles Conservation Project |publisher=World Foundation for Environment and Development |url=http://www.wfed.org/projects/yellowstone/project.htm |date=April 27, 2004 |access-date=March 15, 2007 |url-status=usurped |archive-url=https://web.archive.org/web/20070320104815/http://www.wfed.org/projects/yellowstone/project.htm |archive-date=March 20, 2007 }}</ref> In 2016, researchers from Uppsala University reported the discovery of a class of thermophiles, [[Hadesarchaea]], in Yellowstone's Culex Basin. These organisms are capable of converting carbon monoxide and water to carbon dioxide and hydrogen.<ref name=Baker>{{cite journal |last1=Baker |first1=Brett J. |last2=Saw |first2=Jimmy H. |last3=Lind |first3=Anders E. |last4=Lazar |first4=Cassandra Sara |last5=Hinrichs |first5=Kai-Uwe |last6=Teske |first6=Andreas P. |last7=Ettema |first7=Thijs J.G. |title=Genomic inference of the metabolism of cosmopolitan subsurface Archaea, Hadesarchaea |journal=Nature Microbiology |volume=1 |issue=3 |pages=16002 |date=February 16, 2016 |language=en |doi=10.1038/nmicrobiol.2016.2 |pmid=27572167 |doi-access=free }}</ref><ref name=IBTimes>{{cite web |last=Atherton |first=Matt |url=http://www.ibtimes.co.uk/god-underworld-microbes-hadesarchaea-discovered-living-toxic-gas-deep-below-yellowstone-hot-1543919 |title=God of the underworld microbes Hadesarchaea discovered living on toxic gas deep below Yellowstone hot springs |website=IB Times |date=February 15, 2016 |access-date=February 25, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160229090040/http://www.ibtimes.co.uk/god-underworld-microbes-hadesarchaea-discovered-living-toxic-gas-deep-below-yellowstone-hot-1543919 |archive-date=February 29, 2016 }}</ref>

Non-native plants sometimes threaten native species by occupying 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.<ref name="exotic">{{cite web |url=http://www.nps.gov/yell/naturescience/upload/ExoticVeg_2_1_06.pdf |title=Exotic Vegetation Management in Yellowstone National Park |website=Nature and Science |publisher=National Park Service |date=February 1, 2006 |access-date=March 13, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070612125909/http://www.nps.gov/yell/naturescience/upload/ExoticVeg_2_1_06.pdf |archive-date=June 12, 2007 }}</ref>

=== Fauna ===
{{Main|Animals of Yellowstone|Birds of Yellowstone National Park|History of wolves in Yellowstone|Yellowstone Park Bison Herd|Small mammals of Yellowstone National Park|Fishes of Yellowstone National Park|Amphibians and reptiles of Yellowstone National Park}}
Yellowstone is widely considered to be the finest [[megafauna]] wildlife habitat in the [[contiguous United States|lower 48 states]]. There are almost 60 species of [[mammal]]s in the park, including the [[northwestern wolf|Rocky Mountain wolf]], [[Mountain coyote|coyote]], the [[Canada lynx|Canadian lynx]], [[cougar]]s, and [[American black bear|black]] and [[grizzly bear]]s.<ref name="facts"/> Other large mammals include the [[American bison|bison]] (often referred to as buffalo), [[Rocky Mountain elk|elk]], [[moose]], [[mule deer]], [[white-tailed deer]], [[mountain goat]], [[pronghorn]], and [[bighorn sheep]].
[[File:American Bison (Yellowstone).jpg|thumb|left|[[American bison]]]]

The [[Yellowstone Park bison herd]] is the largest public herd of American bison in the United States. 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. The Yellowstone Park bison herd reached a peak in 2005 with 4,900 animals. Despite a summer estimated population of 4,700 in 2007, the number dropped to 3,000 in 2008 after a harsh winter and controversial brucellosis management strategies which sent hundreds to slaughter.<ref name="bison2">{{cite web |title=Frequently Asked Questions About Bison |website=Nature and Science |publisher=National Park Service |url=http://www.nps.gov/yell/naturescience/bisonqa.htm |date=August 9, 2006 |access-date=April 1, 2007 |url-status=live |archive-url=https://web.archive.org/web/20071013103606/http://www.nps.gov/yell/naturescience/bisonqa.htm |archive-date=October 13, 2007 }}</ref>
[[File:Mother Elk Nursing Her Calf.JPG|thumb|[[Elk]] mother nursing her calf]]

The Yellowstone Park bison herd is believed to be one of only four free-roaming and genetically pure herds on public lands in North America. The other three herds are the [[Henry Mountains bison herd]] of [[Utah]], at [[Wind Cave National Park]] in [[South Dakota]], and in [[Elk Island National Park]] in Alberta.<ref>{{cite news |last=Prettyman |first=Brett |title=Moving Bison |newspaper=[[Salt Lake Tribune]] |date=January 10, 2008 |url=http://www.sltrib.com//ci_7924854?IADID=Search-www.sltrib.com-www.sltrib.com |access-date=January 12, 2008 |url-status=live |archive-url=https://web.archive.org/web/20080408132149/http://www.sltrib.com/ci_7924854?IADID=Search-www.sltrib.com-www.sltrib.com |archive-date=April 8, 2008 }}</ref>

The relatively large bison populations are a concern for ranchers, who fear that the species can transmit [[bovine]] diseases to their domesticated cousins. 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 [[Miscarriage|miscarry]]. The disease has little effect on park bison, and no reported cases of transmission from wild bison to domestic livestock have been filed. Elk also carry the disease and are believed to have transmitted the infection to horses and cattle.<ref name="aphis">{{cite web |title=Brucellosis and Yellowstone Bison |website=Brucellosis |publisher=Animal and Plant Health Inspection Service |url=http://www.aphis.usda.gov/vs/nahps/brucellosis/cattle.htm |archive-url=https://web.archive.org/web/20070228214304/http://www.aphis.usda.gov/vs/nahps/brucellosis/cattle.htm |archive-date=February 28, 2007 |access-date=August 24, 2011 }}</ref>

To combat the perceived threat of [[brucellosis]] transmission to cattle, national park personnel regularly corral bison herds back into the park when they venture outside of the area's borders. During the winter of 1996–1997, the bison herd was so large that 1,079 bison that had exited the park were either shot or sent to slaughter.<ref name="aphis"/> [[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.<ref name="aphis"/>
[[File:WolfRunningInSnow.jpg|left|thumb|A reintroduced [[wolf]] in Yellowstone National Park]]

Starting in 1914, to protect elk populations, the U.S. Congress appropriated funds to be used for "destroying wolves, [[prairie dog]]s, 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. Gradually, wolves were virtually [[History of wolves in Yellowstone|eliminated from Yellowstone]].<ref name="dow">{{cite web |title=Defenders of Wildlife |website=A Yellowstone Chronology |url=http://www.defenders.org/wildlife/wolf/ynpchro.html |access-date=March 19, 2007 |archive-url=https://web.archive.org/web/20070607214843/http://www.defenders.org/wildlife/wolf/ynpchro.html |archive-date=June 7, 2007 }}</ref> 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.<ref name="dow"/> After the wolves were extirpated from Yellowstone, the [[coyote]] then became the park's top canine predator. Since the coyote is not able to bring down large animals, this lack of an [[apex predator]] resulted in a marked increase in lame and sick megafauna.{{citation needed|date=February 2022}}

By the 1990s, the Federal government had reversed its views on wolves. In a controversial decision by the [[United States Fish and Wildlife Service|U.S. Fish and Wildlife Service]] (which oversees threatened and endangered species), northwestern 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.<ref name="rmw">{{cite web |title=Rocky Mountain Wolf Recovery 2005 Interagency Annual Report |publisher=U.S. Fish and Wildlife Service, Nez Perce Tribe, National Park Service, Montana Fish, Wildlife & Parks, Idaho Fish and Game, and USDA Wildlife Services |url=http://www.fws.gov/mountain-prairie/species/mammals/wolf/annualrpt05/2005_WOLF_REPORT_TOTAL.pdf |year=2006 |access-date=March 19, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070616094301/http://www.fws.gov/mountain-prairie/species/mammals/wolf/annualrpt05/2005_WOLF_REPORT_TOTAL.pdf |archive-date=June 16, 2007 }}</ref> Almost all the wolves documented were descended from the 66 wolves reintroduced in 1995–96.<ref name="rmw"/> The recovery of populations throughout the states of Wyoming, Montana, and Idaho has been so successful that on February 27, 2008, the U.S. Fish and Wildlife Service removed the Northern Rocky Mountain wolf population from the [[Lists of IUCN Red List endangered species|endangered species list]].<ref name="delisting">{{cite web |title=Final Rule Designating the Northern Rocky Mountain Population of Gray Wolf as a Distinct Population Segment and Removing This Distinct Population Segment From the Federal List of Endangered and Threatened Wildlife |publisher=U.S. Fish and Wildlife Service |date=February 27, 2008 |url=http://www.regulations.gov/fdmspublic/component/main?main=DocumentDetail&o=09000064803cae39 |access-date=June 11, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20090121172210/http://www.regulations.gov/fdmspublic/component/main?main=DocumentDetail&o=09000064803cae39 |archive-date=January 21, 2009 }}</ref> As of January 2023, there are at least 108 wolves in the park in 10 packs.<ref name=":0">{{Cite web |title=Gray Wolf - Yellowstone National Park |url=https://www.nps.gov/yell/learn/nature/wolves.htm |access-date=November 25, 2023 |website=National Park Service |archive-date=November 30, 2023 |archive-url=https://web.archive.org/web/20231130022546/https://www.nps.gov/yell/learn/nature/wolves.htm |url-status=live }}</ref> Wolves in Yellowstone sit at the core of a larger population connected throughout the Greater Yellowstone Ecosystem.<ref name=":0" />
[[File:Black bear sow with cub, Tower Fall (18393659291).jpg|thumb|[[American black bear|Black bear]] and cub near [[Tower Fall]]]]

[[American black bear|Black bears]] are common in the park and were a park symbol due to visitor interaction with the bears starting in 1910. Feeding and close contact with bears has not been permitted since the 1960s to reduce their desire for human foods.<ref name="bbears">{{cite web |title=Black Bears |publisher=National Park Service |url=http://www.nps.gov/yell/naturescience/bbears.htm |date=March 31, 2014 |access-date=April 16, 2014 |url-status=live |archive-url=https://web.archive.org/web/20140418042904/http://www.nps.gov/yell/naturescience/bbears.htm |archive-date=April 18, 2014 }}</ref> Yellowstone is one of the few places in the United States where black bears can be seen coexisting with grizzly bears.<ref name="bbears" /> Black bear observations occur most often in the park's northern ranges, and in the [[Bechler River|Bechler]] area which is in the park's southwestern corner.<ref name="bbinfo">{{cite web |title=Black Bear Information Continued |publisher=National Park Service |url=http://www.nps.gov/yell/naturescience/bbinfo.htm |date=April 3, 2014 |access-date=April 16, 2014 |url-status=live |archive-url=https://web.archive.org/web/20140418053542/http://www.nps.gov/yell/naturescience/bbinfo.htm |archive-date=April 18, 2014 }}</ref>

{{As of|2017}}, an estimated 700 grizzly bears were living in the Greater Yellowstone Ecosystem,<ref>Frank T. van Manen, Mark A. Haroldson, and Bryn E. Karabensh (2018). [https://prd-wret.s3-us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/atoms/files/2017_AnnualReport_Final_tagged_Secured_v3.pdf "Yellowstone Grizzly Bear Investigations 2017: Annual Report of the Interagency Grizzly Bear Study Team"] ({{usurped|1=[https://web.archive.org/web/20181218012656/https://prd-wret.s3-us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/atoms/files/2017_AnnualReport_Final_tagged_Secured_v3.pdf archive]}}). page 23 (of PDF file). U.S. Geological Survey, Wyoming Game and Fish Department, National Park Service, U.S. Fish and Wildlife Service, Montana Fish, Wildlife and Parks, U.S. Forest Service, Idaho Department of Fish and Game, Eastern Shoshone and Northern Arapaho Tribal Fish and Game Department. Retrieved December 19, 2018.</ref> with about 150 grizzlies living wholly or partially within Yellowstone National Park.<ref>[https://www.nps.gov/yell/learn/nature/grizzlybear.htm "Grizzly Bears"]. ''nps.gov''. National Park Service. April 2, 2018. {{usurped|1=[https://web.archive.org/web/20181010113713/https://www.nps.gov/yell/learn/nature/grizzlybear.htm Archived]}} from the original on October 10, 2018. Retrieved December 19, 2018.</ref> The grizzly was initially listed as a threatened species in the [[contiguous United States]] on July 28, 1975, by the Fish and Wildlife Service. The grizzly bear was taken off the [[United States Fish and Wildlife Service list of endangered mammals and birds|endangered species list]] in 2007.<ref name=esl>[https://www.nps.gov/yell/learn/nature/bearesa.htm "Grizzly Bears & the Endangered Species Act"]. ''nps.gov''. National Park Service. October 5, 2018. {{usurped|1=[https://web.archive.org/web/20181013231744/https://www.nps.gov/yell/learn/nature/bearesa.htm Archived]}} from the original on October 13, 2018. Retrieved December 19, 2018.</ref> Opponents of delisting the grizzly expressed concerns that states might once again allow hunting and that better conservation measures were needed to ensure a sustainable population.<ref name="geographic">{{cite news |last=Mott |first=Maryann |title=Bald Eagle, Grizzly: U.S. Icons Endangered No More? |publisher=National Geographic News |date=July 2, 2004 |url=http://news.nationalgeographic.com/news/2004/06/0628_040628_baldeagle.html |access-date=March 19, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20061210164506/http://news.nationalgeographic.com/news/2004/06/0628_040628_baldeagle.html |archive-date=December 10, 2006 }}</ref> A federal district judge overturned the delisting ruling in 2009, reinstating the grizzly. The grizzly was once again removed from the list in 2017.<ref name=esl/> In September 2018, a U.S. district judge ruled that the grizzly's protections must be restored in full, arguing the Fish and Wildlife Service was mistaken in removing the bear from the threatened status list.<ref>{{cite news |url=https://www.nytimes.com/2018/09/25/science/yellowstone-grizzly-hunt.html |title=Hunt of Yellowstone Grizzly Bears Canceled as a Result of Judge's Ruling |newspaper=The New York Times |author=Jim Robbins |date=September 25, 2018 |access-date=September 27, 2018 |archive-date=September 26, 2018 |archive-url=https://web.archive.org/web/20180926182101/https://www.nytimes.com/2018/09/25/science/yellowstone-grizzly-hunt.html |url-status=live }}</ref> Hunting is prohibited within Yellowstone National Park while hunters may transport the carcass through the park with a permit.<ref name=carcass>{{cite web |title=Transporting Carcasses Through Yellowstone |url=https://www.nps.gov/yell/learn/management/transportingcarcasses.htm |publisher=National Park Service |access-date=September 27, 2018 |archive-date=September 27, 2018 |archive-url=https://web.archive.org/web/20180927065758/https://www.nps.gov/yell/learn/management/transportingcarcasses.htm |url-status=live }}</ref>
[[File:Bull Elk herd.jpg|left|thumb|Elk in Hayden Valley]]

Population figures for elk are more than 30,000—the largest population of any large mammal species in Yellowstone. The northern herd has decreased enormously since the mid‑1990s; this has been attributed to wolf predation and causal effects such as elk using more forested regions to evade [[predation]], consequently making it harder for researchers to accurately count them.<ref name="elk count">{{cite news |title=2006–2007 Winter Count of Northern Yellowstone Elk |publisher=National Park Service |date=January 16, 2007 |url=http://www.nps.gov/yell/parknews/nycwwg.htm |access-date=March 19, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070520102047/http://www.nps.gov/yell/parknews/nycwwg.htm |archive-date=May 20, 2007 }}</ref> The northern herd migrates west into southwestern Montana in the winter. The southern herd migrates southward, and the majority of this elk winter on the [[National Elk Refuge]], immediately southeast of Grand Teton National Park. The southern herd migration is the largest mammalian migration remaining in the U.S. outside of Alaska.{{citation needed|date=February 2022}}

In 2003 the tracks of one female lynx and her cub were spotted and followed for over {{convert|2|mi|km}}. Fecal material and other evidence obtained were tested and confirmed to be those of a lynx. No visual confirmation was made, however. Lynx have not been seen in Yellowstone since 1998, though [[DNA]] taken from hair samples obtained in 2001 confirmed that lynx were at least transient to the park.<ref name="lynx">{{cite web |last=Potter |first=Tiffany |title=Reproduction of Canada Lynx Discovered in Yellowstone |website=Nature: Year in Review |publisher=National Park Service |date=April 13, 2004 |url=http://www2.nature.nps.gov/YearinReview/yir2003/07_E.html |access-date=March 19, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070325193828/http://www2.nature.nps.gov/YearinReview/yir2003/07_E.html |archive-date=March 25, 2007 }}</ref> Other less commonly seen mammals include the mountain lion and [[wolverine]]. The mountain lion has an estimated population of only 25 individuals parkwide.<ref name="lion">{{cite web |title=Mountain Lions |publisher=National Park Service |date=July 26, 2006 |url=http://www.nps.gov/yell/naturescience/mtlions.htm |access-date=March 19, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070903154004/http://www.nps.gov/yell/naturescience/mtlions.htm |archive-date=September 3, 2007 }}</ref> Accurate population figures for the wolverine are not known.<ref name="wolverine">{{cite journal |last=Marquis |first=Amy Leinbach |title=Out of Sight, Out of Mind |journal=National Parks |volume=80 |issue=3 |pages=20–21 |date=Summer 2006 }}</ref> These uncommon and rare mammals provide insight into the health of protected lands such as Yellowstone and help managers make determinations as to how best to preserve habitats.
[[File:Antilocapra americana.jpg|thumb|[[Pronghorn]] are commonly found on the grasslands in the park]]

Eighteen species of fish live in Yellowstone, including the core range of the [[Yellowstone cutthroat trout]]—a fish highly sought by [[fishing|anglers]].<ref name="facts"/><ref name="fish">{{cite web |title=Fishing in Yellowstone National Park |publisher=National Park Service |date=April 4, 2007 |url=http://www.nps.gov/yell/planyourvisit/fishing.htm |access-date=March 19, 2007 |url-status=live |archive-url=https://web.archive.org/web/20131109002421/http://www.nps.gov/yell/planyourvisit/fishing.htm |archive-date=November 9, 2013 }}</ref> The Yellowstone cutthroat trout has faced several threats since the 1980s, including the suspected illegal introduction into Yellowstone Lake of [[lake trout]], an [[invasive species]] which consume the smaller cutthroat trout.<ref name="lake trout">{{cite web |title=The Yellowstone Lake Crisis: Confronting a Lake Trout Invasion |publisher=National Park Service |url=http://www.nps.gov/yell/planyourvisit/upload/laketrout2.pdf |year=1995 |access-date=March 19, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070612130055/http://www.nps.gov/yell/planyourvisit/upload/laketrout2.pdf |archive-date=June 12, 2007 }}</ref> Although lake trout were established in [[Shoshone Lake|Shoshone]] and [[Lewis Lake (Wyoming)|Lewis]] lakes (on the Snake River drainage) after U.S. government stocking operations in 1890, it was never officially introduced into the Yellowstone River drainage.<ref>{{cite book |last=Kendall |first=W. C. |title=The Fishes of the Yellowstone National Park |publisher=Department of Commerce, Bureau of Fisheries |location=Washington D.C. |pages=22–23 |year=1915 }}</ref> The cutthroat trout has also faced an ongoing drought, as well as the accidental introduction of a parasite—[[Myxobolus cerebralis|whirling disease]]—which causes a terminal nervous system disease in younger fish. Since 2001, all native sport fish species caught in Yellowstone waterways are subject to catch and release regulations.<ref name="fish"/>

Yellowstone is also home to seven species of reptiles: [[painted turtle]], [[Rubber boa]], [[Crotalus viridis|prairie rattlesnake]], [[bullsnake]], [[sagebrush lizard]], [[Common garter snake#Subspecies|valley garter snake]] and [[Western terrestrial garter snake#Subspecies|wandering garter snake]]. Four species of [[amphibians]] are present: [[boreal chorus frog]], [[tiger salamander]], [[western toad]] and [[columbia spotted frog]].<ref name="reptiles">{{cite web |title=Vital Habitats: Wetlands and Wildlife |publisher=National Park Service |url=http://www.nps.gov/yell/naturescience/upload/vitalhabitats.pdf |access-date=March 19, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070616094258/http://www.nps.gov/yell/naturescience/upload/vitalhabitats.pdf |archive-date=June 16, 2007 }}</ref>

Three hundred eleven species of birds have been reported, almost half of which nest in Yellowstone.<ref name="facts"/> In 1999, twenty-six pairs of nesting [[bald eagle]] were documented. Extremely rare sightings of [[whooping crane]]s have been recorded; however, only three examples of this species are known to live in the Rocky Mountains out of 385 known worldwide.<ref name="eagle">{{cite web |title=Threatened and Endangered Species |publisher=National Park Service |date=July 26, 2006 |url=http://www.nps.gov/yell/naturescience/endangeredbirds.htm |access-date=March 19, 2007 |archive-url=https://web.archive.org/web/20071013103610/http://www.nps.gov/yell/naturescience/endangeredbirds.htm |archive-date=October 13, 2007 |url-status=dead }}</ref> Other birds, considered to be species of special concern because of their rarity in Yellowstone, include the [[common loon]], [[harlequin duck]], [[osprey]], [[peregrine falcon]] and the [[trumpeter swan]].<ref name="concern">{{cite web |title=Species of Special Concern |publisher=National Park Service |date=July 28, 2006 |url=http://www.nps.gov/yell/naturescience/specialconcern.htm |access-date=March 19, 2007 |url-status=live |archive-url=https://web.archive.org/web/20071013103631/http://www.nps.gov/yell/naturescience/specialconcern.htm |archive-date=October 13, 2007 }}</ref>