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Wildlife in the Grand Canyon
The three most common amphibians in the Grand Canyon are the canyon treefrog, red-spotted toad, and Woodhouse’s rocky mountain toad. These amphibians need the Colorado River or perennial tributaries in order to breed, since their egg masses and tadpoles are water bound. However, they are more tolerant of desiccation than most amphibians, and red-spotted toads have been found as far as one-half mile from a known water source. Leopard frogs are very rare in the Colorado River corridor, and are known to exist at only a few sites.
The lush vegetation and diversity of plant species along the riparian zone create many bird habitats in a relatively small area. Of the 355 bird species recorded in the greater Grand Canyon region, 250 are found in the Colorado River corridor. Only 48 bird species regularly nest along the river while others use the river as a migration corridor or as overwintering habitat. The Bald eagle is one species that uses the river corridor as winter habitat. The trout rich waters of the Colorado River provide a perfect food source for the eagles. Since the construction of Glen Canyon Dam, large numbers of waterfowl have begun using the stretch of river below the dam during the winter, peaking in late December and early January. Nineteen species have been regularly reported between Lees Ferry and Soap Creek, at a density of 136 ducks per mile.
There are 33 crustacean species found in the Colorado River and its tributaries within Grand Canyon National Park. Of these 33, 16 are considered true zooplankton organisms. Grand Canyon's crustacean species can be grouped into five major types: Calanoid copepods, Cyclopoid copepods, cladocerans, amphipods, and ostracods. The zooplankton crustaceans constitute a significant food source for larval rainbow trout, larval bluehead and flannelmouth suckers, as well as many benthic invertebrates.
Until Glen Canyon Dam was completed in 1963, the Colorado River’s aquatic system was dominated by native fish. These native species were specifically adapted to highly variable seasonal fluctuations in sediment load, flow, and temperature, and were severely impacted by dramatic changes resulting from the dam. The introduction of non-native fish contributed to competition and direct mortality. Predation on native fish has been documented for channel catfish, black bullhead, brown trout, and rainbow trout, and competition is implied for many species. Of the eight native species found in the River before 1963, three species are now extirpated (the Colorado squawfish, bonytail chub and roundtail chub), two species are federally listed as endangered (the humpback chub and razorback sucker*), and three species (the speckled dace, flannelmouth sucker, and bluehead sucker) still have adequate populations.
Programs to introduce non-native species for sport and food began at the turn of the century. Most releases were cool-water fish, although warm-water fish, including carp and brown trout from the Eastern U.S., were also stocked. Trout were introduced for sport purposes by the National Park Service (NPS), Arizona Game and Fish Department (AGFD), and the US Fish and Wildlife Service (USFWS) in the 1920s. While the NPS ceased stocking in 1964, AGFD continued to plant rainbow trout near Lees Ferry until the 1990's. Twenty-four species of non-native fishes have been reported in Grand Canyon since 1958 with approximately 12 present today. This number may increase in the future, as fish stocked in Lake Mead continue to move upriver into the park.
* some experts believe the razorback sucker has been extirpated from the Colorado River above Diamond Creek.
Insects, Spiders, Centipedes, Millipedes
The insect species commonly found in the river corridor and tributaries are midges, caddis flies, mayflies, stoneflies, black flies, mites, beetles, butterflies, moths, and fire ants. Numerous species of spiders and several species of scorpions including the bark scorpion and the giant hairy scorpion inhabit the riparian zone.
Riparian: Of the 34 mammal species found along the Colorado River corridor, 15 are rodents and eight are bats. Of the rodents, river otters may have disappeared from the park in the last decade and muskrats are extremely rare. However, an increase in the population size and distribution of beavers has occurred seen since the construction of Glen Canyon Dam. Beavers cut willows, cottonwoods, and shrubs for food, and can significantly affect the riparian vegetation. Other rodents, such as antelope squirrels and pocket mice, are mostly omnivorous, using many different vegetation types. Grand Canyon bats typically roost in desert uplands, but forage on the abundance of insects along the river and its tributaries.
In addition to bats, coyotes, ringtails, and spotted skunks are the most numerous riparian predators. They prey on invertebrates, rodents, and reptiles. Raccoon, weasel, bobcat, gray fox, and mountain lion are also present, but are much more rare. Mule deer and desert bighorn sheep are the ungulates that frequent the river corridor. Since the removal of 500 ferral burros in the early 1980's, bighorn sheep numbers have rebounded. Mule deer are generally not permanent residents along the river, but travel down from the rim when food and water resources there become scarce.
Eleven aquatic and 26 terrestrial species of mollusks have been identified in and around Grand Canyon National Park. Of the aquatic species, two are bivalves (clams) and nine are gastropods (snails). All of the aquatic snails located in Grand Canyon are of the subclass Pulmonata. This means that although they are aquatic, they are lung breathers. They do not have gills, but have a large pulmonary sac which they use for gaseous exchange. Three of the nine snail species found here are lymnaeids of the genus Fossaria. Lymnaeid snails have shells that coil to the right. Physids, of which Grand Canyon has five species of the genus Physella, are snails that possess shells that coil to the left. The remaining aquatic snail species is called a planorbid of the genus Gyralus. Planorbid snail shells are coiled in a single plane, appearing flatter than most snails.
The two aquatic bivalves are thought to be introduced species, since they were found in a cobble bar near Lees Ferry just downriver from the Glen Canyon Dam. These two clam species are of the genus Pisidium.
Twenty-six species of terrestrial gastropods have been identified, primarily land snails and slugs. The ambersnail family, Succineidae, is of special interest in Grand Canyon. This family of land snails gets its common name, "amber snail," from the snails' characteristic orange colored shell. One species of amber snail found in the park, the Kanab Ambersnail (Oxyloma haydeni kanabensis), is listed as endangered by the U.S. Fish and Wildlife Service. Only two populations of this species are known to exist.
Riparian: There are a approximately 47 reptile species in Grand Canyon National Park. Ten are considered common along the river corridor and include lizards and snakes. Reptiles use both upland desert and riparian sites, but higher densities are supported in riparian areas due to the rich invertebrate food source and vegetation. Lizard density tends to be highest along the stretch of land between the water's edge and the beginning of the upland desert community. Within this zone, exotic saltcedar (tamarisk) is abundant, which is excellent lizard habitat. One can also find gila monsters and chuckwallas here, the two largest lizards in the Canyon.
Many snake species, which are not directly dependent on surface water, may be found both within the inner gorge and the Colorado River corridor. Since many snakes feed on lizards, higher prey densities along the river probably result in higher snake densities as well. Six rattlesnake species have been recorded in the park. Two are species rarely encountered, the South-western speckled rattlesnake and the Northern black-tailed rattlesnake. The other four rattlesnakes are subspecies of the Western Diamondback rattlesnake complex: the Grand Canyon pink rattlesnake, Great Basin rattlesnake, Mojave "green" rattlesnake, and Hopi rattlesnake. Of these, the Grand Canyon pink rattlesnake is the most common.
As the demand for reptiles in the pet trade increases and collectors seek new sources of supply, many national parks are having problems with illegal reptile collection, especially rattlesnakes. Approaching and feeding wildlife in the park is illegal and poaching is a punishable crime.
Desert Riparian Habitat