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Description
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
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. The eggs and larvae of A. canorus are extremely melanistic more so than those of A. boreas (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).
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).
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.
Originally submitted by: John Romansic and Yair Chaver (first posted 1999-02-21)
Edited by: Kellie Whittaker, Michelle S. Koo (2020-02-12)Species Account Citation: AmphibiaWeb 2020 Anaxyrus canorus: Yosemite Toad <https://amphibiaweb.org/species/135> University of California, Berkeley, CA, USA. Accessed Apr 1, 2023.
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Citation: AmphibiaWeb. 2023. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 1 Apr 2023.
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