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Anaxyrus canorusYosemite Toad

By maria filipowska

Geographic Range

Yosemite toads are found in a small area of the Sierra Nevada Mountains in California. They have never been found outside of California. Anaxyrus canorus range from the Blue Lakes region of Ebbets Pass to Kaiser Pass located near Evolution Lake in the Darwin Canyon area. They are found at high elevations in only two Californian counties, Alpine and Fresno counties. (Hammerson, October 2002; Leonard, 2002)

Habitat

Yosemite toads are found in wet mountain meadows, often near pine forests. Even though they spend most of their time on land, they are never far from a permanent body of water. In their juvenile stage, Yosemite toad tadpoles swim in shallow pools of melted ice water, and in slow moving mountain streams. Anaxyrus canorus live at high elevations, anywhere from 1950 meters to 3450 meters up on a mountain side. These grassland amphibians burrow under the soil, crawl beneath rocks and fallen logs and seek shelter in abandoned rodent holes during the night. (Davidson and Kagarise Sherman, July 1994; Hammerson, October 2002)

  • Aquatic Biomes
  • rivers and streams
  • temporary pools
  • Range elevation
    1950 to 3450 m
    6397.64 to 11318.90 ft

Physical Description

Anaxyrus canorus are moderate size amphibians ranging from 4.5 cm to 7.5 cm. They show the highest degree of sexual dichromatism, different coloration between sexes, found among Californian toads. As in most sexually dimorphic animals, males exhibit brighter colors than females. Yosemite toad males are olive green to yellow green with small dark flecks, while females are gray or brown with large dark spots. (Davidson and Kagarise Sherman, July 1994; Romanisic and Chaver, 2002; Shaffer, et al., 2000; Kagarise Sherman, 1980)

The young tadpoles look nothing like the adult toads, but it only takes them 7 to 9 weeks to metamorphose into adults. Yosemite toads are closely related to three other toads, the black, western and Amargosa toads. Together they make up the "boreas group." The Yosemite toads' high degree of sexual dichromatism distinguishes them from their relatives. Other features that distinguish the A. canorus from closely related species are their smaller size, wider paratoid glands and lack of a vertebral stripe. (Davidson and Kagarise Sherman, July 1994)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • male more colorful
  • Range length
    4.5 to 7.5 cm
    1.77 to 2.95 in

Development

Yosemite toads lay their eggs in shallow pools of water from May to mid August. Eggs hatch in 10 to 12 days and tadpoles metamorphose into adults seven to nine weeks after hatching. The first few years of Anaxyrus canorus lives are not reproductive. Females reach reproductive age at four to six years and males at three to five years. (Davidson and Kagarise Sherman, July 1994)

The biggest cause of mortality among tadpoles is desiccation. When the snowfall is low the pools of water that form in the spring dry up too quickly for the toads to metamorphose in time. Recent drought in California may be one reason this toads' population has greatly declined. (Davidson and Kagarise Sherman, July 1994; Shaffer, et al., 2000)

Reproduction

Yosemite toads spawn, lay eggs, in shallow pools and slow moving streams in mountain meadows. After hibernation the males leave the meadows and search for water. They arrive at their breeding sites several days before the females. Both sexes are active during the day and there are about ten times as many males at breeding sites as females. Males stay at an individual site for a maximum of two weeks and females only for a few days. Both sexes try to increase their fitness by mating as often as possible with as many partners as possible. The males try to attract their mates by emitting very melodious sounds during the day. Many people mistake the mating calls of the Yosemite toads for songs of spring birds. Canorus means "tuneful" in Latin. (Davidson and Kagarise Sherman, July 1994; Hammerson, October 2002; Romanisic and Chaver, 2002)

Breeding season of A. canorus begins in May, when the ice melts and forms shallow pools, and continues until mid August. Like most frogs and toads, Yosemite toads have external fertilization. The females lay their eggs in single or double strands and sometimes in clusters in shallow water and the males fertilize them. Females may lay anywhere from 1500 to 2000 eggs. These hatch in less than a week and a half and metamorphose into adults in about two months. A temperature of below 31 degrees Celsius must be maintained in order for the eggs to develop. For the larvae to survive, a temperature of less than 36 degrees Celsius is necessary. Adults do not seem to react to varying temperatures during their active season; instead they are sensitive to moisture. The females reach reproductive age at four to six years and males at the age of three to five. Anaxyrus canorus have been known to hybridize with Anaxyrus boreas in the northern parts of their range. (Davidson and Kagarise Sherman, July 1994; Hammerson, October 2002; Kagarise Sherman, 1980; Romanisic and Chaver, 2002)

  • Breeding season
    May to mid August
  • Range number of offspring
    1500 to 2000
  • Range time to hatching
    10 to 12 (days till eggs hatch) days
  • Range age at sexual or reproductive maturity (female)
    4 to 6 years
  • Range age at sexual or reproductive maturity (male)
    3 to 5 years

Yosemite toads do not exhibit parental care. After eggs have been fertilized both parents go in search of other mates. (Davidson and Kagarise Sherman, July 1994)

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

B. canorus is a long living species. Females live at least 15 years while males live shorter lives of at least 12 years. (Davidson and Kagarise Sherman, July 1994; Kagarise Sherman, 1980)

  • Range lifespan
    Status: wild
    15 (low) years

Behavior

Yosemite toads are only active during the day. During the night they burrow in soil, under logs, and in rodent tunnels. They are solitary creatures except during the breeding season, when males are found congregated around shallow pools of water emitting their melodious trills. A. canorus start hibernation in late September or early October, and they come out of their deep sleep sometimes in April, May or July depending on temperature. Even though the Yosemite toads keep to themselves they are not territorial. (Davidson and Kagarise Sherman, July 1994; Kagarise Sherman, 1980)

Communication and Perception

During breeding season B. canorus males assemble in the day and call to the females in choruses. Their melodious calls are often mistaken for bird calls. (Davidson and Kagarise Sherman, July 1994; Leonard, 2002)

Food Habits

The feeding patterns of the adult and larvae Yosemite toads differ. Anaxyrus canorus larvae eat plankton and detritus, while the adults are primarily insectivorous. In the summer, hymenopterans are a major part of the toads' diet. Some specific foods of B. canorus are ants, centipedes, spiders, ladybird beetles, mosquitoes, weevils, tenebrionid beetles, and millipedes. (Davidson and Kagarise Sherman, July 1994; Hammerson, October 2002; Romanisic and Chaver, 2002)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods

Predation

It may be that the coloration of B. canorus makes it hard to spot for predators. These toads' main defense mechanisms against predation, however, are their poison glands. Like many other toads, this species has enlarged paratoid glands at the side of its neck. The paratoid glands secrete a white poison that protects the Yosemite toads from prospective predators by causing nausea, inflammation of the mouth, or irregular heart beat. This poses a danger to the toads' predators and can be irritating to humans if it gets into the mouth or eyes. In extreme cases the poison can cause death to its ingestor. The taste of the mucous-like poison is also very unpleasant. (Davidson and Kagarise Sherman, July 1994; Hammerson, October 2002; Leonard, 2002; Romanisic and Chaver, 2002)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

The Yosemite toads and tadpoles provide a minor food source for birds and snakes in the Sierra Nevada Mountain ecosystem. Their number and success may be an indicator of the amount of pollution in that ecosystem, but this has not yet been determined. The toads' soil burrowing habits may also contribute minimally to the aeration of the soil. (Davidson and Kagarise Sherman, July 1994; Hammerson, October 2002)

Economic Importance for Humans: Positive

Yosemite toads may be beneficial to people by controlling populations of insects. The poison in the paratoid glands may also be beneficial once researched.

  • Positive Impacts
  • research and education
  • controls pest population

Economic Importance for Humans: Negative

The poison in the paratoid glands of the Yosemite toads irritates the skin and causes inflammation, and may be dangerous to humans if it gets into the eyes and mouth. (Leonard, 2002)

Conservation Status

In addition to its listing as an endangered animal on the IUCN Red List, Anaxyrus canorus is a Category 2 candidate for listing as an Endangered Species by the United States fish and Wildlife Service. Vehicular traffic kills, prolonged periods of drought, and disease all claim partial responsibility in the rapid decline of Anaxyrus canorus. Attempts are being made at various zoological institutions throughout the U.S. to successfully breed and reintroduce this species back into its native range. (Romanisic and Chaver, 2002)

Contributors

David Armitage (editor), Animal Diversity Web.

maria filipowska (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

choruses

to jointly display, usually with sounds, at the same time as two or more other individuals of the same or different species

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

detritus

particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

insectivore

An animal that eats mainly insects or spiders.

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

phytoplankton

photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)

poisonous

an animal which has a substance capable of killing, injuring, or impairing other animals through its chemical action (for example, the skin of poison dart frogs).

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

saltatorial

specialized for leaping or bounding locomotion; jumps or hops.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

soil aeration

digs and breaks up soil so air and water can get in

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

References

Davidson, C., C. Kagarise Sherman. July 1994. "Bufo canorus - Yosemite Toad" (On-line ). Species Tour of California. Accessed 3/19/03 at http://ice.ucdavis.edu/Toads/canorus.html.

Hammerson, G. October 2002. "Bufo canorus" (On-line ). NatureServe Explorer: An online encyclopedia of life. Accessed 03/19/03 at http://www.natureserve.org/explorer.

Kagarise Sherman, C. 1980. A comparison of the natural history and mating system of two Anurans : Yosemite toads (Bufo canorus) and black toads (Bufo exsul). Thesis (Ph. D.)--University of Michigan: 378-394.

Leonard, W. 2002. "Yosemite Toad" (On-line ). eNature.com. Accessed 03/19/03 at http://www.enature.com.

Romanisic, J., Y. Chaver. 2002. "Bufo canorus" (On-line). Amphibia Web. Accessed March 19, 2003 at http://amphibiaweb.org/.

Shaffer, B., G. Fellers, A. Magee, R. Voss. 2000. The genetics of amphibian declines: population substructure and molecular differentiation in the Yosemite toad, Bufo canorus (Anura, Bufonidae) based on single-strand conformation polymorphism analysis (SSCP) and mitochondrial DNA sequence data. Molecular Ecology, 9/3: 245-257.

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