The Colorado River toad (Bufo=Incilius alvarius) is a large mainly terrestrial toad ranging in length from 4.3 to 7.4 inches (110 to 187 mm). It has leathery skin that ranges in color from olive brown to black with a few, low rounded bumps and enlarged glands on the back of the limbs. Females contain reddish-colored warts in straight lines on the back. Tadpoles of this species have a brassy coloration, rounded tail, flattened body, and can reach a size of 2.2 inches (57 mm) total length.
The Colorado River toad is not federally listed. It is listed as threatened in New Mexico. Natureserve ranks the Colorado River toad as secure on a national and global level. Additionally, it is ranked as secure in Arizona, imperiled in New Mexico, and possibly locally extinct in California.
The Colorado River toad is a nocturnal toad in the family Bufonidae. Common names for this species are the Colorado River toad and the Sonoran Desert Toad. The first described specimen was a female collected in Fort Yuma, Imperial county, California, in 1855.
The Colorado River Toad breeds from May through August in ponds, slow-moving streams, temporary pools, or man made structures that hold water. In Arizona, it usually breeds in temporary pools formed by monsoon rains. Breeding and chorusing activity usually occurred one to three nights following rainfall events. However, it has also been found that while breeding activity is stimulated by rainfall, it is not necessary for reproductive activity. The persistence of the Colorado River toad over a 6-year time period has been observed in the absence of successful breeding through many seasons.Clutch size is between 7,500 and 8,000 eggs per female. Eggs are deposited in shallow water in pools. When compared to other frogs and toads, the Colorado River toad develops from zygote to hatchling at a remarkably fast rate, taking less than 30 days for an egg to develop into a froglet.
Colorado River toad adults are active foragers and feed on invertebrates, lizards, small mammals, and amphibians. Colorado River toads have been known to eat beetles, wasps, ants, bees, termites, sun spiders, true bugs, butterflies and moths, spiders, mites, scorpions, grasshoppers, locusts, crickets, millipedes, and centipedes. Tadpoles eat algae and aquatic insects. The Colorado River toad is able to eat prey that is protected by sting mechanisms or defensive secretions.
Habitat loss and alteration in the LCR region likely have had an impact on Colorado River toad populations. Extensive use of pesticides after World War II may have had an effect on this species. Nonnative species to the LCR that have an effect on many native species, such as the American Bullfrog and the spiny softshell turtle, may also affect Colorado River toad populations along the LCR. Illegal collection of the Colorado River toad for use in the drug trade is also a threat to this species.Predators include raccoons, possibly birds, other mammals, and reptiles. It has been observed that the defensive posture and skin toxins of the Colorado River toad protects it from the striped skunk. It is likely that adult Colorado River toads are safe from most predators due to the toxicity of their secretions and their large size.
Updated December 20, 2013
The historical range of the Colorado River toad in California extended along the floodplain of the Lower Colorado River (LCR) and in the southern Imperial Valley. Historically, it was documented on the LCR from Fort Yuma to the Blythe-Ehrenberg Region. The range likely extended along the LCR to extreme southern Nevada, near Fort Mohave. The Lower Colorado River Multi-Species Conservation Program (LCR MSCP) planning area is on the western edge of the historical range of the Colorado River toad.
The Colorado River toad is currently restricted to the Sonoran Desert in lowland and riparian areas of southern Arizona and adjacent corners of southeastern California, southwestern New Mexico, and northeastern Baja California, through most of Sonora, and to seven miles west of Guamuchil, Sinoloa Mexico. This species is found at elevations ranging from above sea level to 1 mile (1600 m). The Colorado River toad is common throughout its range in Arizona but has declined in California and New Mexico.
Click on the map below to see the distribution range of the Colorado River Toad within the LCR MSCP area using the interactive GIS map.
The Colorado River toad is a mainly terrestrial toad that occurs primarily in desert habitat, including mesquite/creosote lowlands, but also inhabits arid grasslands, oak-woodland habitat, riparian areas, and pine-oak-juniper forest. This species is found at elevations ranging from above sea level to 1 mile (1610 m). The Colorado River toad has been observed in pine-oak woodlands, characterized by high densities of Chihuahua pine, Mexican pinyon, alligator bark juniper, and various oaks, and a native grassland in Chihuahuan desert scrub. This species has also been observed associated with Agave, Ephedra, Prosopis, Slasola, Yucca, Gutierrezia, and grasses. The Colorado River toad may have also expanded its range to agricultural areas when large-scale conversion of native habitat to agriculture took place.
Breeding habitat includes seasonal and permanent pools. Preferred Colorado River toad habitat is described as damp areas near permanent springs or manmade watering holes. They are also known to utilize artificial water bodies, such as canals, flood control impoundments, stock tanks, water irrigation ditches, and reservoirs. Agricultural drains, dam seepages, irrigation canals, and backwaters along the lower Colorado River are described as "marginal habitat" for this species. Habitat for the Colorado River toad when dormant or hiding places during active period includes rodent burrows, rocky outcroppings, or in hollows under watering troughs.
LCR MSCP Conservation Measures
The Habitat Conservation Plan provides conservation measures specific to each species. Listed below are the species specific conservation measures for the Colorado River toad. Click on the arrows to expand the table.
|CRTO1—Conduct research to better define the distribution, habitat requirements, and factors that are limiting the distribution of the Colorado River toad|
Develop and implement a multiyear integrated research program to determine the range, status, habitat requirements, population biology, factors that currently limit Colorado River toad abundance and distribution, and factors that have contributed to the decline of the species in the LCR MSCP planning area.
|CRTO2—Protect existing unprotected occupied Colorado River toad habitat|
Based on results of research conducted under conservation measures CRTO1 and within funding constraints of the LCR MSCP, protect existing unprotected occupied Colorado River toad habitat that is located through the research program.
|CRTO3—Conduct research to determine feasibility of establishing the Colorado River toad in unoccupied habitat|
Conduct research necessary to determine the feasibility for successfully establishing the Colorado River toad in unoccupied habitat. If feasible, implement a pilot introduction into unoccupied habitat, and monitor the success of methods and establishment of the Colorado River toad in unoccupied habitat.
Research and Monitoring Activities
The LCR MSCP conducts a variety of research and monitoring activities along the LCR encompassing both MSCP and non-MSCP species. For a complete list of all activities, please see the Research and Monitoring Activities web page.
The following list includes different research and monitoring activities for amphibians. Click on the link for more information.
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