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North American Amphibians
Distribution and Diversity
By David M. Green, Linda A. Weir, Gary S. Casper, Michael J. Lannoo
UNIVERSITY OF CALIFORNIA PRESSCopyright © 2013 The Regents of the University of California
All rights reserved.
FROGS OF NORTH AMERICA
Readers seeking supporting citations for the frog species accounts in this section may turn to the Notes section at the back of this book, as well as the original, unabridged species accounts with extensive citations on pages 382–600 in Amphibian Declines, from which most of the information in these accounts is derived.
Ascaphus montanus Nielson, Lohman, and Sullivan, 2001
Rocky Mountain Tailed Frog
Rocky Mountain Tailed Frogs occur in southeast Washington and northeastern Oregon, in west central and northern Idaho, in southeastern British Columbia and in western Montana. The population in the Columbia Mountains of British Columbia appears to be isolated from the rest of the range. Rocky Mountain Tailed Frogs are found up near to timberline, which is at an elevation of 2100 m in the Wallowa Mountains.
Both adult Rocky Mountain Tailed Frogs and their tadpoles occupy cold, swift mountain streams with cobble substrates. Tadpoles typically require permanent water. Adult Rocky Mountain Tailed Frogs seldom move more than 10 m upstream or downstream, although they may move preferentially into smaller, more shaded streams during the summer. After heavy rains or dews, especially during the spring and autumn, adults and juveniles may be found on land in moist woods.
The specialized habitat of Rocky Mountain Tailed Frogs makes them vulnerable to habitat degradation and destruction following timber harvest or road construction near their habitats. Sedimentation and warmer water temperatures in streams tend to be associated with lower abundances of Rocky Mountain Tailed Frogs.
In Canada, Rocky Mountain Tailed Frogs are considered to be endangered, and they are on the British Columbia Red List of Threatened and Endangered Species.
Ascaphus truei Stejneger, 1899
Coastal Tailed Frog
Coastal Tailed Frogs occur from sea level to near the timberline in the Coast Mountains of British Columbia north to the Nass River, in the Cascades Range, in the Olympic Mountains, and in the Coast Range in the U.S. south to the Mendocino Range in California. This range is divided by fjords, deep valleys, and major rivers such as the Columbia and Fraser, which limit the dispersal of Coastal Tailed Frogs.
Coastal Tailed Frogs occupy cold, swift mountain streams with cobble substrates. Their tadpoles typically require permanently running streams. Severe floods that scour stream bottoms can remove entire tadpole populations. Adults may move into smaller, more shaded streams during the summer, as they avoid warm water temperatures. After heavy rains or dews, adult Coastal Tailed Frogs may be found on land in moist woods, especially during the spring and autumn.
Lower abundances of Coastal Tailed Frogs have been documented following timber harvest and local road construction. They have been characterized as both environmentally sensitive and resilient to large-scale disturbance. They were one of the first vertebrates to recover following the 1980 eruption of Mt. St. Helens.
Coastal Tailed Frogs are listed a species of Special Concern under the Canadian Species at Risk Act and are on British Columbia's Blue List of species of Special Concern.
Anaxyrus americanus Holbrook, 1836
American Toads are found throughout most of North America east of the central U.S. plains and Canadian prairies. Their northern limit goes from north of Lake Winnipeg to Hudson Bay at the Winisk River in Ontario and the Great Whale River in Québec and east to Lake Melville on the Labrador coast. To the south, American toads are absent from much of the Gulf and Atlantic Coastal Plains, including Florida, except for an extension south through eastern Mississippi and eastern Lousiana to about Lake Pontchartrain. They are absent from eastern Long Island, and are introduced on Anticosti Island and the island of Newfoundland. American Toads are found at elevations over 1524 m in the Great Smoky Mountains.
American Toads are to be found in a great range of habitats, including gardens, fields, lawns, and barnyards. Adults congregate to breed in shallow, often grassy, areas within lakes, ponds, streams, and assorted types of ephemeral wetlands, preferentially not overly shaded by trees. American Toads are mainly nocturnal and seek cover during the day under stones, boards, woodpiles, walkways, porches, or other cover. These toads establish small home ranges of 6 m2 or more in size and will repeatedly use particular hiding places. During wet periods, American Toads may travel great distances, easily exceeding 1 km. They are tolerant of brackish estuarine waters.
American Toads are considered the common and abundant "hoptoad" of the East. They tolerate humans well and are frequently abundant throughout their range. They do not appear to be as sensitive to habitat fragmentation as are many other species of co-occurring amphibians, and they are often the first amphibian to reinvade clear-cut or burned areas of forest. Tadpoles are, however, susceptible to the low pH caused by acid precipitation and chemical contaminants.
Nowhere is the American Toad considered to be under any threat of disappearance, although population sizes can fluctuate dramatically.
Anaxyrus baxteri Porter, 1968
Wyoming Toads are native only to the flood plains of the Big and Little Laramie rivers at an elevation of 2164 m in the Laramie Basin of Wyoming.
Wyoming Toads frequent a variety of wetland habitats in shortgrass prairie, including lakes, ponds, streams, marshes, and roadside ditches. Adults live close to water and are almost always restricted to the shoreline. Wyoming Toads deposit their eggs in shallow areas of ponds and small lakes, and metamorphosis usually takes place in early July, which corresponds to the annual bloom of small black flies, possibly a food source for young toads. Wyoming Toads have been found near pocket gopher or ground squirrel burrows in the spring and fall, and it is assumed that these are used for hibernation.
The abundance of Wyoming Toads has greatly declined, and they have disappeared from most of their former ranges. The only known current localities in nature for Wyoming Toads are in and around Mortenson Lake. Considering their limited numbers, low genetic diversity, reliance on captive breeding, and continuing problems with disease, Wyoming Toads are likely the most endangered amphibian species in North America.
Wyoming Toads are listed as Endangered under the U.S. Endangered Species Act.
Anaxyrus boreas Baird and Girard, 1852
Western Toads occur throughout most of the mountainous regions of western North America. Their range encompasses the entire Pacific Coast from Prince William Sound in southern Alaska to extreme northern Baja California, including Haida Gwaii and Vancouver Island. To the east, they can be found to the Rocky Mountain foothills, including north central New Mexico and western Colorado, Wyoming, and Montana, and western and central Alberta. Western toads are also found in far northern British Columbia, southern Yukon, and extreme southwestern Northwest Territories, generally associated with warm springs in that region. They can occur at elevations to nearly 3400 m in western Wyoming.
Adult Western Toads breed in wetlands in still or barely moving water, typically ponds and small lakes, streams, rain pools, and ditches. Juveniles move from their natal wetlands to nearby terrestrial sites or to other nearby wetlands. Adult Western Toads are often found at the water's edge or basking on partially submerged logs in the spring and early summer. Later in the year, they use a variety of habitat types from upland aspen/conifer stands to rocky areas. During cold weather, Western Toads use gopher and ground squirrel holes as retreats. At higher elevations, Western Toads hibernate in rock-lined chambers near creeks, in ground squirrel burrows, under the root systems of evergreen trees, under large boulders, and in beaver and muskrat lodges.
Severe declines and extirpations of many populations of Western Toads have occurred in areas where they once were abundant, especially in the Rocky Mountains of Colorado and Wyoming. In New Mexico, a number of Western Toad populations have declined rapidly and are now thought to be extirpated. Western Toads are currently abundant within the blast zone of the 1980 Mount St. Helens eruption; however, they are rare in the lowlands of Puget Sound in Washington and the Fraser Valley of British Columbia. Habitat degradation and destruction, including fish introductions and disturbances due to livestock, fungal infections and other pathogens, acid and mineral pollution from mine water drainage, and increased ultraviolet radiation, is contributing most to the decline of Western Toads.
The U.S. Fish and Wildlife Service lists Western Toads in Colorado, New Mexico, and Wyoming as a candidate species for listing. The Colorado Division of Wildlife and the New Mexico Department of Game and Fish list Western Toads as Endangered, and Western Toads are a Protected Species in Wyoming. The Utah Division of Wildlife Resources, as well as the U.S. Bureau of Land Management, has listed them as Sensitive in Utah. Western Toads are listed as a species of Special Concern under the Canadian Species at Risk Act, though British Columbia considers them not to be at risk.
Anaxyrus californicus Camp, 1915
Arroyo Toads occur in southwestern California and adjacent northern Baja California in Mexico, (not shown) mostly on the coastal slopes. They also occupy a few drainages on the desert slopes of the San Gabriel and San Bernardino ranges in California.
Arroyo Toads are closely associated with low-gradient drainages that have extensive terrace systems, braided channels, and large areas of fine sediment deposits that are episodically reworked by flooding. They construct shallow burrows within the riparian zone, where they shelter by day during their active season.
Arroyo Toads have declined in abundance, often to extirpation, at most historical sites. Surviving populations have suffered because of drought, development, and adverse land-use and water-management practices, which include the widespread alteration of the middle reaches of larger drainages by dams and flood control projects. These practices have highly fragmented the current distribution of Arroyo Toads through the loss of coastal lowland habitats. Many isolated populations are either restricted to small headwater drainages above impoundments, where conditions are marginal, or confined to narrow riparian corridors along larger drainages that are subject to extensive disturbance from water-management practices, gravel mining, urbanization, and military training.
Arroyo Toads are listed in the U.S. as Endangered.
Anaxyrus canorus Camp, 1916
Yosemite Toads are restricted to high elevations, from about 2000 to 3500 m, in the central Sierra Nevada Mountains of California from Ebbetts Pass to the Spanish Mountain area.
Yosemite Toads inhabit high-elevation, open, montane meadows; willow thickets; and adjoining forests. Although adult Yosemite Toads spend little time in water, they are seldom found more than 100 m away from permanent lakes, ponds, or streams. During the day, adults take cover in rodent burrows, under surface objects, and in willow thickets.
Populations of Yosemite Toads have disappeared from about half of their former range, largely at lower elevations on the western edge of their distribution. Yosemite Toads may have declined in abundance because of disease, drought, or airborne contaminants; livestock grazing may also contribute to their decline because of trampling, alteration of meadow habitat, and possible lowered water quality. Yosemite Toads may also be subject to increased predation by introduced stocked fish and by increasing numbers of Common Ravens.
The State of California lists Yosemite Toads as a Species of Special Concern. The U.S. Fish and Wildlife Service considers Yosemite Toads a candidate species under the Endangered Species Act.
Anaxyrus cognatus Say, 1823
Great Plains Toad
Great Plains Toads occur across the southern Canadian Prairies and the Great Plains of the U.S. from southeast Alberta, southern Saskatchewan, and eastern Montana to the southwestern corner of Manitoba and western Minnesota; south to western Oklahoma and northern Texas; west to the Imperial Valley of California and up the Colorado River though eastern Nevada and southern Utah. Their range extends south to central Mexico (not shown). Great Plains Toads generally are found at elevations less than 1900 m but go up to near 2500 m in the San Luis Valley of Colorado.
Great Plains Toads are found in shortgrass and tallgrass prairies, sandhills, desert mesquite, or desert scrub, but rarely in upland woodlands. They are associated with temporary ponds, irrigation ditches, and bottom lands. Great Plains Toads are tolerant of agriculture and urban conditions. They are proficient burrowers and will form deep burrows in the shape of an inverted question mark, with the toad positioned at the upper, terminal end.
Despite being described as common in many portions of their range, Great Plains Toads are fossorial and difficult to monitor except during spring breeding. In some portions of their range, populations may be scattered and isolated. Population densities are known to fluctuate widely in association with periodic droughts.
Great Plains Toads currently receive no federal or state protection in the U.S. They are, however, listed in Canada as a species of Special Concern under the Species at Risk Act. In Alberta, they are recognized as a species that may be at risk and in Manitoba as Threatened, but they are not listed as a species at risk in Saskatchewan.
Anaxyrus debilis Girard, 1854
Chihuahuan Green Toad
Chihuahuan Green Toads range from southwestern Kansas and adjacent southeastern Colorado south into Mexico (not shown) through central and western Texas, eastern and southern New Mexico, and southeastern Arizona.
Chihuahuan Green Toads are found in arid regions below elevations of about 1500 m in open, grassy plains, native prairie, desert grasslands, mesquite and creosote bush brushlands, and playa bottom grasslands, especially along the valleys of small creeks. Chihuahuan Green Toads often take refuge under rocks or in existing rodent or other burrows and may occur in grasslands that have been converted to agriculture but where herbicide and/or pesticide levels do not exceed lethal limits.
Localized populations of Chihuahuan Green Toads have likely declined in recent years because of the disappearance of their habitat, especially from the conversion and disappearance of wetlands and low-lying areas that the toads use in reproduction. Chihuahuan Green Toads are localized but frequently abundant in remaining areas of suitable habitat.
Chihuahuan Green Toads are listed as Protected in Kansas.
Anaxyrus exsul Myers, 1942
Black Toads are native only to the Deep Springs Valley in east central California. There is also a population of Black Toads inhabiting a flowing well near Salt Lake in Death Valley National Park that has been introduced.
Black toads inhabit the margins of marshes, streams, and sloughs associated with desert springs, where there is an abundance of wetland vegetation, including sedges, rushes, bulrushes, watercress, and rabbitsfoot grass. Because the surrounding desert is dry and cold, Black Toads are aquatic and may never go more than 12 m from standing water. Adults generally are diurnal but they may be active during the morning and early evening hours at air temperatures between 17 and 22°C.
The entire natural range of Black Toads encompasses approximately 15 hectares, one of the smallest ranges for any North American amphibian. As with any species with such a highly restricted distribution, there is concern that a catastrophic event or introduction of a disease or predator could eliminate the entire species.
Black Toads are listed as Threatened by the California Fish and Game Commission.
Anaxyrus fowleri Hinckley, 1882
Fowler's Toads occur throughout most of eastern North America south of the Great Lakes, as well as the northern shore of Lake Erie, but largely excluding the southern Atlantic Coastal Plain and the Florida Peninsula. The western edge of the range of Fowler's Toads runs approximately from eastern Texas and Oklahoma northeast across central Missouri to southeastern Iowa, avoiding Kansas. This boundary, though, is ill defined because of the intergradation of Fowler's Toads with the more westerly occurring Woodhouse's Toads.
Excerpted from North American Amphibians by David M. Green, Linda A. Weir, Gary S. Casper, Michael J. Lannoo. Copyright © 2013 The Regents of the University of California. Excerpted by permission of UNIVERSITY OF CALIFORNIA PRESS.
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