Fauna of North America

The wildlife of North America can be grouped within two large regions—the Nearctic realm, which covers most of North America from the Arctic to northern Mexico, and the Neotropical realm, which covers southern Mexico and all Central America. Species in the Nearctic region are similar to those of Eurasia and North Africa, and originally reached North America from Eurasia by passing over the Bering Strait land bridge that once connected Siberia and Alaska, about sixty million years ago. Species in the Neotropical zone are distinctly different from Nearctic wildlife and reached Central America and Mexico by gradual movement up the isthmus of Panama from South America.

North America’s fauna also can be grouped by regions that reflect such climatic influences as latitude, the position of mountain ranges and oceans, and the plants and trees that grow in that area (grasslands, desert, forest, or tundra). Generally, arctic animals are found to the far north, and on the highest slopes of mountains. As one goes farther south, or farther down the sides of mountains, the animals to be found will be those of the forest, grasslands, or desert environments.

Arctic Tundra

Animals of the far north are similar to those found in Eurasia and are well adapted to their cold, treeless environment. Many of these animals evolved from Ice Age species as the glaciers that once covered North America slowly retreated northward. They are large in size and thickly furred, allowing them to maximize conservation of body heat. Large herbivores such as musk oxen and caribou graze on grasses, lichens, and mosses and are, in turn, a food source for polar bears and arctic wolves. Smaller predators, such as the arctic white fox, feed on arctic hares and small rodents, such as voles, lemmings, or the arctic ground squirrels that subsist upon the small shrubs, berries, and grass seeds of the tundra.

Seals and whales proliferate in the Arctic seas. Birdlife in the Arctic tundra is nearly absent in the winter months, with the exception of willow ptarmigans and snowy owls. In the three to four months of summer, several bird species use the region as a breeding ground where young can be hatched and fed with the abundant insect life that emerges during the long and warmer days of summer. Among these migratory species are many varieties of waterfowl, including Canada geese, snow geese, whooping swans, trumpeter swans, phalaropes, plovers, and arctic terns.

The Arctic has experienced more rapidly warming temperatures than any other region of the world. This has caused ice caps and glaciers to melt and shrink at a rate of 12 to 13 percent per decade. These environmental changes are also changing the habits and habitats of fauna in the region, often leaving animals more vulnerable to predation because of less sea ice coverage. However, it can also impact predatory animals who rely on the sea ice for other purposes. Polar bears, for example, rely on sea ice to hunt. Because there is less ice, polar bears have been forced to fast for longer periods of time as they often struggle to find food. This also affects their mating, breeding, and, therefore, their population. One study documented a 40 percent population loss from 2000 to 2010. Other species are experiencing similar impacts.

Forests

Farther south, below the tree line, coniferous northern forests of fir, spruce, cedar, hemlock, and pine provide shelter and food for the moose, mule deer, and snowshoe hares that browse on the needles of these trees. Squirrels, chipmunks, and porcupines also thrive in the forests of the far north. Predators of this region include martens, fishers, lynx, wolves, weasels, red foxes, and wolverines. Ponds, rivers, marshes, and swamps are common in this habitat, and provide homes for beavers, muskrats, river otters, mink, and such common fish species as whitefish, perch, pickerel, and pike.

Bird species native to the boreal forest include jays (Canada, blue, and gray), thrushes, finches, nuthatches, loons, osprey, ravens, and crows. A wide variety of songbirds (warblers) and some hummingbirds nest in the boreal woods in the summer months.

The eastern half of North America, from southern Canada to Florida, was once thickly covered by deciduous forests of maple, oak, beech, ash, sycamore, hickory, and other trees that shed their leaves in the winter. Where this forest remains, it provides food for a wide variety of mammals, including black bears, red foxes, raccoons, red and gray squirrels, mink, muskrats, jackrabbits, cottontail rabbits, groundhogs, chipmunks, mice, moles, bobcats, skunks, ermine, opossums, and porcupines. Fish species common to the rivers of eastern and southeastern North America include catfish, suckers, and gar. Several species of salamanders and turtles live in the marshes, streams, and rivers of the deciduous forests, especially in the Appalachians. Waterfowl such as kingfishers, herons, ducks, and grebes also live along the waterways of the hardwood forest region.

Grasslands

The prairies in the center of North America provide abundant grasses and other herbaceous plants for many small mammals and grazing animals. Jackrabbits, badgers, prairie chickens, and small rodents such as pocket gophers, prairie dogs, and Richardson’s ground squirrels, feed on grass and roots, as do such larger herbivores as pronghorn antelope and the American bison. The numerous small rodents and the openness of the grasslands provide optimal habitat conditions for such raptors as owls, hawks, and falcons. Waterfowl nest in the many seasonal watering holes (sloughs) that dot the prairies, although farm drainage and extended periods of drought have greatly reduced this habitat. Seeds and insects are plentiful in the grasslands, supporting such bird species as grouse, quail, partridge, and finches.

Rocky Mountains

The high mountains that run along the western side of North America are inhabited by a number of unique species. Bighorn sheep, Rocky mountain goats, mule deer, and elk graze on the grasses of the foothills and slopes of the mountains. Kodiak bears, grizzly bears, and mountain lions prey upon the grazing animals, and bald and golden eagles subsist upon the ground squirrels, marmots, voles, shrews, and pikas that live in the grasses and scattered forests of the lower mountain slopes. Dipper birds feed from the fast-running mountain streams and are found nowhere else on the continent.

Southwestern Deserts

A large number of animals have adapted to the lack of vegetation and water that exists in much of the southwestern United States and Mexico. Kangaroo rats, pocket mice, jackrabbits, armadillos, peccaries, ring-tailed cats, and ground squirrels all survive in that hostile environment. Predators include bobcats, desert foxes, badgers, and coyotes.

The most prolific forms of wildlife in the arid deserts of southernmost North America are the reptiles, including many different species of lizards, rattlesnakes, toads, and iguanas. Because they can only be active when the outside air temperature provides warmth for basic body functions, reptiles and amphibians are quite rare in the most northern parts of the continent but thrive in the arid and hot southern parts of North America. Roadrunners are a major bird predator of these reptiles, along with eagles and hawks.

Neotropical Forests

The tropical rain forests of Central America and southern Mexico have an astonishing variety of wildlife. The forest canopy has abundant bird life in the form of macaws, parrots, turkey vultures, and flycatchers. Monkeys of many varieties (spider, howler, squirrel, and capuchin), as well as sloths and tamarinds, also live in the canopy, feeding on the many fruiting trees. On the floor of the forest, many varieties of ants, spiders, beetles, and chiggers provide food for smaller predators such as anteaters and various species of bats. A number of animals indigenous to South America have adapted to and thrive in Central America, including tapirs, capybaras, pacas, jaguars, ocelots, and agoutis.

Coastal Regions

The beaches, shores, lagoons, and marshes that line the North American continent are home to many kinds of animals that feed upon the ocean life or the intertidal plants and animals that live in the midzone between fresh and saltwater. Many kinds of migratory waterfowl exploit the small crustaceans and mollusks that live at the water’s edge, including sandpipers, stilts, curlews, and flamingos. Seals, sea otters, and walruses are found on both coasts in the north of the continent, while Steller’s sea lions and California sea lions are found only on the Pacific coast. The lagoons of the southern Atlantic coast and the Gulf of Mexico are home to alligators, pelicans, egrets, and spoonbills.

Changes in ocean water temperatures are impacting the varieties of marine life and the availability of food for some predators. For example, some marine species that live in colder waters are moving further north to escape rising temperatures. Examples include black sea bass, Atlantic salmon, butterfish, and lobsters. One study found, though, that these migratory shifts, which would seem to benefit these populations, can negatively impact abundance. Furthermore, rising sea levels have caused habitat changes for some species, such as eroding nesting areas for sea turtles and shorebirds. Changing sea levels have also caused freshwater habitats to become contaminated with saltwater as the oceans push into the land, which can impact freshwater populations.

Principal Terms

Grazing Species: Animals that eat grass; some are wild, but many grazers have also been domesticated

Herbivore: An animal that only eats plants

Migratory Species: A species of animal that lives part of the year in one habitat and then moves to another habitat for another part of the year

Predator: An animal that obtains food by hunting other animals

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