Mammals are vertebrate animals constituting the class Mammalia, characterized by the presence of mammary glands which in females produce milk for feeding their young, a neocortex, fur or hair, three middle ear bones. These characteristics distinguish them from reptiles and birds, from which they diverged in the late Triassic, 201–227 million years ago. There are around 5,450 species of mammals; the largest orders are the rodents and Soricomorpha. The next three are the Primates, the Cetartiodactyla, the Carnivora. In cladistics, which reflect evolution, mammals are classified as endothermic amniotes, they are the only living Synapsida. The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period around 300 million years ago, this group diverged from the sauropsid line that led to today's reptiles and birds; the line following the stem group Sphenacodontia split off several diverse groups of non-mammalian synapsids—sometimes referred to as mammal-like reptiles—before giving rise to the proto-mammals in the early Mesozoic era.
The modern mammalian orders arose in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs, have been among the dominant terrestrial animal groups from 66 million years ago to the present. The basic body type is quadruped, most mammals use their four extremities for terrestrial locomotion. Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale—the largest animal on the planet. Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale. All modern mammals give birth to live young, except the five species of monotremes, which are egg-laying mammals; the most species-rich group of mammals, the cohort called placentals, have a placenta, which enables the feeding of the fetus during gestation. Most mammals are intelligent, with some possessing large brains, self-awareness, tool use. Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals and echolocation.
Mammals can organize themselves into fission-fusion societies and hierarchies—but can be solitary and territorial. Most mammals are polygynous. Domestication of many types of mammals by humans played a major role in the Neolithic revolution, resulted in farming replacing hunting and gathering as the primary source of food for humans; this led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, the development of the first civilizations. Domesticated mammals provided, continue to provide, power for transport and agriculture, as well as food and leather. Mammals are hunted and raced for sport, are used as model organisms in science. Mammals have been depicted in art since Palaeolithic times, appear in literature, film and religion. Decline in numbers and extinction of many mammals is driven by human poaching and habitat destruction deforestation. Mammal classification has been through several iterations since Carl Linnaeus defined the class.
No classification system is universally accepted. George Gaylord Simpson's "Principles of Classification and a Classification of Mammals" provides systematics of mammal origins and relationships that were universally taught until the end of the 20th century. Since Simpson's classification, the paleontological record has been recalibrated, the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself through the new concept of cladistics. Though field work made Simpson's classification outdated, it remains the closest thing to an official classification of mammals. Most mammals, including the six most species-rich orders, belong to the placental group; the three largest orders in numbers of species are Rodentia: mice, porcupines, beavers and other gnawing mammals. The next three biggest orders, depending on the biological classification scheme used, are the Primates including the apes and lemurs. According to Mammal Species of the World, 5,416 species were identified in 2006.
These were grouped into 153 families and 29 orders. In 2008, the International Union for Conservation of Nature completed a five-year Global Mammal Assessment for its IUCN Red List, which counted 5,488 species. According to a research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495 species included 96 extinct; the word "mammal" is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from the Latin mamma. In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes and therian m
North American cougar
The North American cougar, is a subspecies of the cougar in North America. It was once found in eastern North America, is still prevalent in the western half of the continent, it is the biggest wild cat in North America. The subspecies P. c. couguar encompasses populations found in the United States, western Canada, the critically endangered Florida panther population, the extinct eastern cougar and Central America, South America northwest of the Andes Mountains. Western populations of the cougar are seen in the former range of the extinct eastern population; the population in Costa Rica had been listed as least concern by the IUCN Red List. Puma concolor costaricensis had been regarded as a subspecies in Central America; as of 2017, P. c. cougar was recognised as being valid by the Cat Classification Taskforce of the Cat Specialist Group. The North American cougar weighs 25 -- 80 kg. Females average 50 kg, about the same as a jaguar in the Chamela-Cuixmala Biosphere Reserve on the Mexican Pacific coast.
The cougar can be found in various habitats. Several populations still exist and are thriving in the Western United States and Western Canada, but the North American cougar was once found in eastern portions of the United States, it was believed to be extirpated there in the early 1900s. Cougars in Michigan were thought to have been extinct in the early 1900s. Today there is evidence to support that cougars could be on the rise in Mexico and could have a substantial population in years to come; some mainstream scientists believe that small relict populations may exist in the Appalachian Mountains and eastern Canada. Recent scientific findings in hair traps in Fundy National Park in New Brunswick have confirmed the existence of at least three cougars in New Brunswick; the Ontario Puma Foundation estimates that there are 850 cougars in Ontario. Reported sightings of cougars in the eastern United States continue today, despite their status as extirpated. WisconsinGenetic analysis of DNA from a cougar sighting in Wisconsin in 2008 indicated that a cougar was in Wisconsin and that it was not a captive animal.
The cougar is thought to have migrated from a native population in the Black Hills of South Dakota. Whether other breeding, cougars are present is uncertain. A second sighting was reported and tracks were documented in a nearby Wisconsin community. A genetic analysis could not be done and a determination could not be made; this cougar made its way south into the northern Chicago suburb of Wilmette. On June 3, 2013, a verified sighting was made in Wisconsin; the cougar was photographed by an automatic trail camera, confirmed by DNR biologists in October, 2013. TennesseeOn September 26, 2015, a hair sample was submitted by a hunter in Carroll County, Tennessee. Bobcats in this state reside in regions that were once roamed by cougars. IllinoisOn April 14, 2008, a cougar triggered a flurry of reports before being cornered and killed in the Chicago neighborhood of Roscoe Village while officers tried to contain it; the cougar was the first sighted in the city limits of Chicago since the city was founded in 1833.
On November 22, 2013, a cougar was found on a farm near Morrison in Illinois. An Illinois Department of Natural Resources officer subsequently shot and killed the cougar after determining it posed a risk to the public. ConnecticutIn 2011, a cougar was sighted in Greenwich and killed by an SUV in Milford after travelling 1,500 mi from South Dakota. While the origins of these animals are unknown, some cougar experts believe some are captive animals that have been released or escaped; this felid hunts at night and may sometimes travel long distances in search of food. Its average litter size is three cubs. Like other cougars, it is fast, can maneuver quite and skillfully. Depending on the abundance of prey such as deer, it may share the same prey as the jaguar in Central or North America. Aside from the jaguar, sympatric predators include American black bears. Cougars are known to prey on bear cubs. Rivalry between the cougar and grizzly was a popular topic in North America. Fights between them were staged, those in the wilderness were recorded by people, including Natives.
Though conservation efforts of the cougar have decreased against the "more appealing" jaguar, it is hunted less because it has no spots, is thus less desirable to hunters. Shasta South American cougar American cheetah Felinae Wright, Bruce S; the Eastern Panther: A Question of Survival. Toronto: Clarke and Company, 1972. Eastern Cougar Foundation National Heritage Information Centre: General Element Report: Puma concolor New York State Department of Environmental Conservation: Eastern Cougar Fact Sheet The IUCN Red List of Threatened Species Photograph of a black or dark cougar in Costa Rica Largest North American Cat: Mountain Lion
Yellowstone National Park
Yellowstone National Park is an American national park located in Wyoming and Idaho. It was established by the U. S. Congress and signed into law by President Ulysses S. Grant on March 1, 1872. Yellowstone was the first national park in the U. S. and is widely held to be the first national park in the world. The park is known for its wildlife and its many geothermal features Old Faithful geyser, one of its most popular features, it has many types of ecosystems. It is part of the South Central Rockies forests ecoregion. Native Americans have lived in the Yellowstone region for at least 11,000 years. Aside from visits by mountain men during the early-to-mid-19th century, organized exploration did not begin until the late 1860s. Management and control of the park fell under the jurisdiction of the Secretary of the Interior, the first being Columbus Delano. However, the U. S. Army was subsequently commissioned to oversee management of Yellowstone for a 30-year period between 1886 and 1916. In 1917, administration of the park was transferred to the National Park Service, created the previous year.
Hundreds of structures have been built and are protected for their architectural and historical significance, researchers have examined more than a thousand archaeological sites. Yellowstone National Park spans an area of 3,468.4 square miles, comprising lakes, canyons and mountain ranges. Yellowstone Lake is one of the largest high-elevation lakes 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 geysers and hydrothermal features are in Yellowstone, fueled by this ongoing volcanism. 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. In 1978, Yellowstone was named a UNESCO World Heritage Site. Hundreds of species of mammals, birds and reptiles have been documented, including several that are either endangered or threatened.
The vast forests and grasslands include unique species of plants. Yellowstone Park is the largest and most famous megafauna location in the contiguous United States. Grizzly bears and free-ranging herds of bison and elk live in this park; the Yellowstone Park bison herd is the largest public bison herd in the United States. Forest fires occur in the park each year. Yellowstone has numerous recreational opportunities, including hiking, boating 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 access the park by way of guided tours that use either snow coaches or snowmobiles; the park contains the headwaters of the Yellowstone River. Near the end of the 18th century, French trappers named the river Roche Jaune, a translation of the Hidatsa name Mi tsi a-da-zi. American trappers rendered the French name in English as "Yellow Stone". Although it is believed that the river was named for the yellow rocks seen in the Grand Canyon of the Yellowstone, the Native American name source is unclear.
The human history of the park begins at least 11,000 years ago when Native Americans 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 11,000 years ago; these Paleo-Indians, of the Clovis culture, used the significant amounts of obsidian found in the park to make 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. By the time white explorers first entered the region during the Lewis and Clark Expedition in 1805, they encountered the Nez Perce and Shoshone tribes. While passing through present day Montana, the expedition members heard of the Yellowstone region to the south, but they did not investigate it. 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 became the park, during the winter of 1807–1808. He observed at least one geothermal area near Tower Fall. After surviving wounds he suffered in a battle with members of the Crow and Blackfoot tribes in 1809, Colter described a place of "fire and brimstone" that most people dismissed as delirium. Over the next 40 years, numerous reports from mountain men and trappers told of boiling mud, steaming rivers, petrified trees, yet most of these reports were believed at the time to be myth. After an 1856 exploration, mountain man Jim Bridger reported observing boiling springs, spouting water, a mountain of glass and yellow rock; these reports were ignored because Bridger was a known "spinner of yarns". In 1859, a U. S. Army Surveyor named Captain William F. Raynolds embarked on a two-year survey of the northern Rockies. After wintering in Wyoming, in May 1860, Raynolds and his party – which included naturalist Ferdinand Vandeveer Hayden and guide Jim B
The northwestern wolf known as the Mackenzie Valley wolf, Alaskan timber wolf, Canadian timber wolf, or northern timber wolf, is a subspecies of gray wolf in western North America. It ranges from the upper Mackenzie River Valley; this wolf is recognized as a subspecies of Canis lupus in the taxonomic authority Mammal Species of the World. The subspecies was first written of by Scottish naturalist Sir John Richardson in 1829, he chose to give it the name occidentalis in reference to its geographic location rather than label it by its color, as it was too variable to warrant such. According to one source, phylogenetic analyses of North American gray wolves show that there are three clades corresponding to C. l. occidentalis, C. l. nubilus and C. l. baileyi, each one representing a separate invasion into North America from distinct Eurasian ancestors. C. l. occidentalis, the most northwestern subspecies, is descended from the last gray wolves to colonize North America. It crossed into North America through the Bering land bridge after the last ice age, displacing C. l. nubilus populations as it advanced, a process which has continued until present times.
Along with C. l. nubilus, C. l. occidentalis is the most widespread member of the five gray wolf subspecies in North America, with at least six different synonyms. Northwestern wolves are one of the largest subspecies of wolves. In British Columbia, five adult females averaged 42.5 kg and ten adult males averaged 51.1 kg, with a weight range for all adults of 38.6 to 61.4 kg. In Yellowstone National Park, adult females were reported to average 41 kg and adult males averaged 50 kg, with a mean adult body mass in winter of 43.4 kg. More recent studies have reported the average height and weight of males and females in the north-west of the United States, where the males were between 68 and 91.5 cm tall and weighed between 45 and 66 kg, while the females were between 35 and 50 cm and weighed 36-59 kg. Based on known reported adult average body masses, this would make the northwestern wolf the largest-bodied wolf subspecies, in comparison the mean adult weights of its two nearest rivals in size, the Eurasian wolf and the Interior Alaskan wolf, was reported as 39 kg and 40 kg, respectively.
Sir John Richardson described the northwestern wolf as having a more robust build than the European wolf, with a larger, rounder head and a thicker, more obtuse muzzle. Its ears are shorter, its fur bushier. In Yellowstone National Park, artificially relocated northwestern wolves have been well-documented feeding on elk, they stampede the herd using pack teamwork to separate the younger elk from the adults. They will charge young calves separated from their parents. Winter-weakened or sick elk play an important part of Yellowstone wolf diets and it is estimated that over 50 percent of winter-weakened or sick elk in Yellowstone are killed by wolves. Of these, about 12 percent of carcasses were scavenged by other predators, including ravens, bald eagles, black bears, grizzly bears, coyotes. In the same national park, wolves prey on bison, though such attacks involve sick animals or calves, as bison can kill wolves with their hooves, they are present in Canadian or British safari parks including Longleat and Parc Omega
The Snake River is a major river of the greater Pacific Northwest region in the United States. At 1,078 miles long, it is the largest tributary of the Columbia River, in turn the largest North American river that empties into the Pacific Ocean; the Snake River rises in western Wyoming flows through the Snake River Plain of southern Idaho, the rugged Hells Canyon on the Oregon–Idaho border and the rolling Palouse Hills of Washington, emptying into the Columbia River at the Tri-Cities, Washington. The Snake River drainage basin encompasses parts of six U. S. is known for its varied geologic history. The Snake River Plain was created by a volcanic hotspot which now lies underneath the Snake River headwaters in Yellowstone National Park. Gigantic glacial-retreat flooding episodes that occurred during the previous Ice Age carved out canyons and waterfalls along the middle and lower Snake River. Two of these catastrophic flooding events, the Missoula Floods and Bonneville Flood affected the river and its surroundings.
Prehistoric Native Americans lived along the Snake starting more than 11,000 years ago. Salmon from the Pacific Ocean spawned by the millions in the river, were a vital resource for people living on the Snake downstream of Shoshone Falls. By the time Lewis and Clark explored the area, the Nez Perce and Shoshone were the dominant Native American groups in the region. Explorers and fur trappers further changed and used the resources of the Snake River basin. At one point, sign language used by the Shoshones representing weaving baskets was misinterpreted to represent a snake, giving the Snake River its name. By the middle 19th century, the Oregon Trail had become well established, bringing numerous settlers to the Snake River region. Steamboats and railroads moved agricultural products and minerals along the river throughout the 19th and early 20th centuries. Starting in the 1890s, fifteen major dams have been built on the Snake River to generate hydroelectricity, enhance navigation, provide irrigation water.
However, these dams blocked salmon migration above Hells Canyon and have led to water quality and environmental issues in certain parts of the river. The removal of several dams on the lower Snake River has been proposed, in order to restore some of the river's once-tremendous salmon runs. Formed by the confluence of three tiny streams on the southwest flank of Two Oceans Plateau in Yellowstone National Park, western Wyoming, the Snake starts out flowing west and south into Jackson Lake, its first 50 miles run through Jackson Hole, a wide valley between the Teton Range and the Gros Ventre Range. Below the tourist town of Jackson, the river turns west and flows through Snake River Canyon, cutting through the Snake River Range and into eastern Idaho, it receives the Hoback and Greys Rivers before entering Palisades Reservoir, where the Salt River joins at the mouth of Star Valley. Below Palisades Dam, the Snake River flows through the Snake River Plain, a vast arid physiographic province extending through southern Idaho south-west of the Rocky Mountains and underlain by the Snake River Aquifer, one of the most productive aquifers in the United States.
Southwest of Rexburg, the Snake is joined from the north by Henrys Fork. The Henrys Fork is sometimes called the North Fork of the Snake River, with the main Snake above their confluence known as the "South Fork". From there it turns south, flowing through downtown Idaho Falls past the Fort Hall Indian Reservation and into American Falls Reservoir, where it is joined by the Portneuf River; the Portneuf River Valley is an overflow channel that in the last glacial period carried floodwaters from pluvial Lake Bonneville into the Snake River altering the landscape of the Snake River Plain through massive erosion. From there the Snake resumes its journey west, it is interrupted by several major cataracts, the largest being 212-foot Shoshone Falls, which marked the upriver limit of migrating salmon. A short distance downstream. Near Twin Falls, the Snake approaches the southernmost point in its entire course, after which it starts to flow west-northwest; the Snake continues through its canyon, receiving the Malad River from the east near Bliss and the Bruneau River from the south in C.
J. Strike Reservoir, it passes through an agricultural valley about 30 miles southwest of Boise and flows west into Oregon, before turning north to define the Idaho–Oregon border. Here the Snake River doubles in size as it receives several major tributaries – the Owyhee from the southwest the Boise and Payette rivers from the east, further downstream the Malheur River from the west and Weiser River from the east. North of Boise, the Snake enters Hells Canyon, a steep, rapid-strewn gorge that cuts through the Salmon River Mountains and Blue Mountains of Idaho and Oregon. Hells Canyon is one of the most rugged and treacherous portions of the course of the Snake River, posing a major obstacle for 19th-century American explorers. Here the Snake is impounded by Hells Canyon and Brownlee Dams, which together make up the Hells Canyon Hydroelectric Project. At the halfway point in Hells Canyon, in one of the most remote and inaccessible sections of its course, the Snake River is joined from the east by its largest tributary, the Salmon River.
From there, the Snake begins to form the Washington–Idaho border, receiving the Grande Ronde River from the west before receiving the Clearwater River from the east at Lewiston, which marks the head of navigation on the Snake. The river leaves Hells Canyon and turns west, winding through the Palouse Hills of eastern Washington; the Lower Snake River Project's four dams and
U.S. Route 287
U. S. Route 287 is a north–south United States highway, it is 1,791 miles long. It serves as the major truck route between Fort Worth and Amarillo and between Fort Collins and Laramie, Wyoming; the highway is broken into two segments by Yellowstone National Park, where an unnumbered park road serves as a connector. The highway's northern terminus is in Choteau, Montana, 100 miles south of the Canadian border, at an intersection with US 89, its southern terminus is in Port Arthur, Texas at an intersection with State Highway 87, five miles up the Sabine River from the Gulf of Mexico. It intersects its parent route US 87 twice, overlapping it from Amarillo to Dumas and crossing it in Denver, Colorado. US 287 is the shortest route between Dallas-Fort Worth. US 287 originates at its southern terminus in Port Arthur as a branch of SH 87. From Port Arthur, US 287 runs concurrently with US 69 and US 96 to Lumberton, where US 96 diverges to the northeast and the co-signed US 287/US 69 continues northwesterly until US 287 and US 69 diverge in Woodville.
Continuing northwesterly, US 287 merges with Interstate 45 in Corsicana and follows the Interstate to Ennis, where it branches off and continues through Waxahachie, crossing I-35E and continuing north through Tarrant County, where it encounters and merges with three different Interstates. From Fort Worth, US 287 continues north to Wichita Falls and continues just south of the Oklahoma border before entering the Texas Panhandle. A section of US 287, between Midlothian and Waxahachie, was dedicated as the Chris Kyle Memorial Highway, in honor of fallen SEAL Chris Kyle, whose hometown was Midlothian; the highway continues through Amarillo, where it intersects I-40, runs north to Kerrick and crosses into neighboring Oklahoma. In Oklahoma, US 287 remains within Cimarron County, located at the end of the Panhandle. After crossing the state line north of Kerrick, the highway intersects SH 171 at its southern terminus. US 287 continues northwesterly, crossing the Beaver River, toward the county seat.
On the east side of town, the highway runs concurrently with US 56, US 64, US 412, SH 3. These five highways enter the traffic circle in downtown Boise City. US 287 emerges from the north side of the circle, as well as US 385 and SH 3; these three highways head north to the Colorado state line. SH 3 ends there, while US US 385 continue onward into Colorado. From Oklahoma, US 287 and US 385 enter into a rural part of Colorado, they continue in a north/northwest direction through the state. The two highways pass through the town of Campo, make an interchange with US 160 on the outskirts of Springfield. In Lamar and Carlton, the highways make an interchange with US 50. Here US 385 heads east on US 50, US 287/US 50 continue to the north. Just outside the town the highways make a sharp turn toward the west, the road heading north is SH 196. South of Wiley, US 50 heads west. East of Eads, US 287 turns toward the west again merging with SH 96. In Eads, SH 96 continues toward the west. Near Kit Carson, US 287 again turns toward the west and merges with US 40.
Near Limon, the two highways make two interchanges with I-70 before passing through Limon. The two highways merge with I-70. Near the outskirts of Denver US 36 merges with the group of highways making the road, I-70/US 287/US 36/US 40. Just past E-470, I-70 and US 36 split to follow a more northerly course, while US 287 and US 40 continue west into Downtown Denver on Colfax Avenue; the I-25, US 6, US 87, US 85 interchange marks US 287's second junction with its parent route, US 87. Shortly thereafter, at a cloverleaf interchange with Federal Boulevard, SH 88 runs south, US 40 continues west on Colfax, US 287 turns toward the north on Federal Boulevard. After crossing US 36, US 287 turns west onto 120th Avenue where it overlaps SH 128. Just before meeting US 36 again in Broomfield, US 287 bends back to the north, leaving SH 128 which continues west through an interchange with SH 121 and US 36. At Baseline Road in Lafayette, SH 7 joins US 287 for about a mile, before SH 7 splits to the west on Arapahoe Avenue towards Boulder.
It intersects SH 119 as it enters Longmont on Main Street, it intersects SH 66 at the north edge of town. The road bypasses Berthoud en route to Loveland, where US 287 splits into the pair of one-way streets Lincoln Avenue and Cleveland Avenue, it divides the Loveland cemetery. This is the only cemetery in the US with a US Highway dividing it. Continuing north, US 287 passes through Fort Collins on College Avenue, merging with SH 14 at Jefferson Street. On the edge of the mountains at Ted's Place, SH 14 splits and heads west into Poudre Canyon, while US 287 continues north into Wyoming; the section of US 287 between Fort Collins and Laramie, carries heavy truck traffic and is regarded as quite dangerous. US 287 enters Wyoming through a pass between the Laramie Mountains to the east and the Medicine Bow Mountains to the west. In Laramie, US 287 crosses I-80 and merges with US 30 and the two highways continue to head north. After passing Medicine Bow, these highways turn west-southwest and return to I-80 near Walcott, where they merge with the interstate west until Rawlins.
US heads into the town. US 287 merges with Wyoming Highway 76, WYO 82, WYO 30 for a short distance just outside Rawlins, though WYO 76 ends when US 287 branches to the northwest as a stand-alone highway, it is po
The bald eagle is a bird of prey found in North America. A sea eagle, it forms a species pair with the white-tailed eagle, its range includes most of Canada and Alaska, all of the contiguous United States, northern Mexico. It is found near large bodies of open water with an abundant food supply and old-growth trees for nesting; the bald eagle is an opportunistic feeder which subsists on fish, which it swoops down and snatches from the water with its talons. It builds the largest nest of any North American bird and the largest tree nests recorded for any animal species, up to 4 m deep, 2.5 m wide, 1 metric ton in weight. Sexual maturity is attained at the age of four to five years. Bald eagles are not bald; the adult is brown with a white head and tail. The sexes are identical in plumage; the beak is hooked. The plumage of the immature is brown; the bald eagle is both the national bird and national animal of the United States of America. The bald eagle appears on its seal. In the late 20th century it was on the brink of extirpation in the contiguous United States.
Populations have since recovered and the species was removed from the U. S. government's list of endangered species on July 12, 1995 and transferred to the list of threatened species. It was removed from the List of Endangered and Threatened Wildlife in the Lower 48 States on June 28, 2007; the plumage of an adult bald eagle is evenly dark brown with a white tail. The tail is moderately long and wedge-shaped. Males and females are identical in plumage coloration, but sexual dimorphism is evident in the species, in that females are 25% larger than males; the beak and irises are bright yellow. The legs are feather-free, the toes are short and powerful with large talons; the developed talon of the hind toe is used to pierce the vital areas of prey while it is held immobile by the front toes. The beak is hooked, with a yellow cere; the adult bald eagle is unmistakable in its native range. The related African fish eagle has a brown body, white head and tail, but differs from the bald in having a white chest and black tip to the bill.
The plumage of the immature is a dark brown overlaid with messy white streaking until the fifth year, when it reaches sexual maturity. Immature bald eagles are distinguishable from the golden eagle, the only other large, non-vulturine raptorial bird in North America, in that the former has a larger, more protruding head with a larger beak, straighter edged wings which are held flat and with a stiffer wing beat and feathers which do not cover the legs; when seen well, the golden eagle is distinctive in plumage with a more solid warm brown color than an immature bald eagle, with a reddish-golden patch to its nape and a contrasting set of white squares on the wing. Another distinguishing feature of the immature bald eagle over the mature bird is its black, yellow-tipped beak; the bald eagle has sometimes been considered the largest true raptor in North America. The only larger species of raptor-like bird is the California condor, a New World vulture which today is not considered a taxonomic ally of true accipitrids.
However, the golden eagle, averaging 4.18 kg and 63 cm in wing chord length in its American race, is 455 g lighter in mean body mass and exceeds the bald eagle in mean wing chord length by around 3 cm. Additionally, the bald eagle's close cousins, the longer-winged but shorter-tailed white-tailed eagle and the overall larger Steller's sea eagle, may wander to coastal Alaska from Asia; the bald eagle has a body length of 70–102 cm. Typical wingspan is between 1.8 and 2.3 m and mass is between 3 and 6.3 kg. Females are about 25% larger than males, averaging as much as 5.6 kg, against the males' average weight of 4.1 kg. The size of the bird varies by location and corresponds with Bergmann's rule, since the species increases in size further away from the Equator and the tropics. For example, eagles from South Carolina average 3.27 kg in mass and 1.88 m in wingspan, smaller than their northern counterparts. One field guide in Florida listed small sizes for bald eagles there, at about 4.13 kg. Of intermediate size, 117 migrant bald eagles in Glacier National Park were found to average 4.22 kg but this was juvenile eagles, with 6 adults here averaging 4.3 kg.
Wintering eagles in Arizona were found to average 4.74 kg. The largest eagles are from Alaska, where large females may weigh more than 7 kg and span 2.44 m across the wings. A survey of adult weights in Alaska showed that females there weighed on average 5.35 kg and males weighed 4.23 kg against immatures which averaged 5.09 kg and 4.05 kg in the two sexes. An Alaskan adult female eagle, considered outsized we