hear call (86.4K RM file)

[call details here]

Description
A small to medium-sized toad, from 50-75 mm in length. Female and young may have many blotches on a pale background, paratoids are usually tan-colored, and the dorsal stripe is usually narrow or absent. The males are yellow-green or dark olive above, with dark blotches virtually absent or reduced to small scattered flecks. Males and females have pale throats (Stebbins 1985).

The Yosemite toad can be distinguished from its closest relative, the Western toad (Anaxyrus boreas), by its smaller size and lack of a vertebral stripe. It also has wider parotoid glands than the Western toad, with a smaller gap between the glands (Stebbins 1985).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: United States

U.S. state distribution from AmphibiaWeb's database: California

	View distribution map in BerkeleyMapper.
	View Bd and Bsal data (81 records).

Endemic to the boreal zone of the central Sierra Nevada mountain range of California. Found mostly at elevations of 8,500-10,000 ft (Karlstrom 1973). Lives in wet, relatively open mountain meadows, never far from a permanent water source. Found in damp areas under logs, stones, or other objects, and in rodent tunnels (Karlstrom 1962).

Life History, Abundance, Activity, and Special Behaviors
Anaxyrus canorus eggs often occur in clusters, unlike the eggs of the closely related A. boreas, which are always laid in long strings (Karlstrom 1962).

Active in the daytime, especially during the breeding period, which starts as soon as shallow ice-melt pools form in the spring. Breeding call is a mellow, sustained, musical trill of 10-20 or more notes.

Eats a variety of insects, centipedes, and spiders, and is in turn preyed upon by garter snakes, birds, and by Rana muscosa, the Mountain yellow-legged frog (Karlstrom 1962).

Larva
The eggs and larvae of A. canorus are extremely melanistic, more so than those of A. boreas (Karlstrom 1962).

Trends and Threats
This species has been declining rapidly and few populations remain. At a Tioga Pass Meadow site, calling males dropped from a mean of 275.5 ±83.1 between 1974 and 1978 to only 28 in 1982. By 1990, 47% of 75 historic site in the species range lacked signs of the toads. Many hypotheses have been proposed to explain the decline, including increased predation, and disease caused by increased stress (such as "red-leg" disease, caused by Aeromonas hydrophilia infection). Perhaps fluctuations in yearly snowfall disrupt reproduction, or even an increase in the chance of summer frost (causing high egg mortality). Too little snowfall may cause their breeding ponds to dry up in the summer before tadpoles can metamorphose. Too much snowfall may shorten the breeding season, preventing tadpoles from metamorphosing completely before the onset of cold fall weather. It is possible that simply studying and handling the toads could contribute to their decline (Sherman and Morton 1993). Karltsrom (1962) suggested that vibrations caused by vehicles passing near breeding sites may reduce their reproductive efficiency. He also noticed that males ceased calling when vehicles drove by on nearby roads. However, no relationship between distance from the nearest road and population declines has been found. Also, habitat disturbance since the mid 1970's has been relatively light, suggesting that habitat destruction is not causing the decline (Sherman and Morton 1993).

Relation to Humans
Named and renowned for its melodious call, which is unique enough that one could mistake it for a bird call (Karlstrom 1962). The name canorus means "tuneful" in Latin (Karlstrom 1973).

Hear Yosemite Toad calls at the Western Sound Archive.

Possible reasons for amphibian decline

Disturbance or death from vehicular traffic
Prolonged drought
Disease

Comments
The extent of sexual dichromatism in Anaxyrus canorus is rare among frogs (including other toads). However, the color differences between males and females do not seem to help the male toad distinguish between sexes, as many observations have been made of these toads attempting to mate with other species, even dead toads (Karlstrom 1962).

This toad is a member of the "boreas group" together with A. boreas (Western toad), A. exsul (Black toad), and A. nelsoni (Amargosa toad) (Blair 1964).

This species was featured in News of the Week 3 June 2024:

There are many iconic amphibian species around the world, and when they disappear, people notice. The Yosemite toad (Anaxyrus canorus) is endemic to California’s Sierra Nevada mountains, and suffered mass die-offs in the late 1970s. Dodge et al (2024) investigated the historical and contemporary effects of Batrachochytrium dendrobatidis (Bd), which causes a fatal amphibian disease called chytridiomycosis on the Yosemite toad. When global amphibian declines were first noticed in the 1970s and 1980s, it was decades before Bd was discovered (1998). This study used a retrospective analysis to determine Bd presence/absence on 719 museum specimens collected between 1915 and 2005, and on an additional 1,678 samples collected from live animals in the wild (2004–2012). Their study found that: 1) Bd emerged coincident with historical declines; 2) Bd is currently widely distributed throughout the species range; 3) life stage, elevation, and precipitation regime were associated with Bd infection likelihood; and, 4) the juvenile life stage was the most highly infected, with some having Bd infection loads surpassing a mortality threshold identified in other species. Thus, Bd may have played a significant yet unrecognized role in the decline of the Yosemite toad, and may continue to affect survival, recruitment, and extinction risk. These represent key insights for efforts to recover this species across its historical range and may also be important in hundreds of other species that declined before Bd was discovered. (Written by Vance Vredenburg)

See another account at californiaherps.com.

References

Blair, F. W. (1964). ''Evidence bearing on the relationships of the Bufo boreas group of toads.'' Texas Journal of Science, 16(2), 181-192.

Camp, C. L. (1916). ''Description of Bufo canorus, a new toad from Yosemite National Park.'' University of California Publications in Zoology, 17, 59-62.

Cunningham, J. D. (1963). ''Additional observations on the ecology of the Yosemite Toad, Bufo canorus.'' Herpetologica, 19(1), 56-61.

Drost, C. A., and Fellers, G. M. (1996). "Collapse of a regional frog fauna in the Yosemite area of the California Sierra Nevada, USA." Conservation Biology, 10(2), 414-425.

Karlstrom, E. L. (1962). The Toad Genus Bufo in the Sierra Nevada of California: Ecological and Systematic Relationships. University of California Press, Berkeley, California.

Karlstrom, E. L. (1963). ''Bufo canorus.'' Catalog of American Amphibians and Reptiles. W. J. Riemer, eds., American Society of Ichthyologists and Herpetologists, 132.1-132.2.

Mullally, D. P. (1953). ''Observations on the ecology of the toad Bufo canorus.'' Copeia, 1953(3), 182-183.

Sherman, C. K., and Morton, M. L. (1993). ''Population declines of Yosemite Toads in the eastern Sierra Nevada of California.'' Journal of Herpetology, 27(2), 186-198.

Stebbins, R. C. (1985). A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin, Boston.

Species Account Citation: AmphibiaWeb 2024 Anaxyrus canorus: Yosemite Toad <https://amphibiaweb.org/species/135> University of California, Berkeley, CA, USA. Accessed Jul 26, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 26 Jul 2024.

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