YOSEMITE TOAD } Bufo canorus
DESCRIPTION: The Yosemite toad is a small to medium-sized toad (two to three inches long) with exceptionally smooth skin. Males and females look nothing alike: the females are larger, with a strikingly colored mosaic of dark blotches on an olive-tan background; adult males are smaller and mature to a color ranging from dull yellow to olive green to bright lemon with black speckles.
HABITAT: Yosemite toads occur from the upper montane into the subalpine zone, just below timberline. Their preferred habitat is wet, montane meadows and lakeshores, among lodgepole pines. During breeding season they may be found in pools, small, slow-moving streams, or boggy meadows.
RANGE: The Yosemite toad inhabits a 130-mile-long segment of the central Sierra Nevada of California, from Alpine County to Fresno County, at elevations of 6,400 to 11,300 feet.
MIGRATION: Yosemite toads do not really migrate, as their hibernation sites are within 100 meters from breeding ponds.
BREEDING: Yosemite toads breed from early May to July, depending upon the elevation and amount of snowfall the previous winter. Almost immediately following snowmelt, males and females make their way to breeding ponds from their winter hibernation sites. Breeding normally takes place in shallow pools fed by melting snow. Males arrive first and call from the shoreline to attract a mate or search silently. Fertilization takes place externally, with sperm released onto the eggs as they are laid in shallow water.
LIFE CYCLE: These toads are active for only four to five months a year, when they reproduce and eat for hibernation. Eggs hatch in one week, with the tadpoles metamorphosing into young toads five to seven weeks later. After making the transition to land, young toads have four to six weeks to feed before hibernation. They are sexually mature after three to five years for males and four to six years for females.
FEEDING: Toads normally consume a variety of arthropods, including ants, beetles, millipedes, flies, spiders, and even bees and wasps. They hunt by staying still until a prey animal approaches, and then capturing it with their sticky tongue.
THREATS: The Yosemite toad is imperiled by introduced fish, pesticides and other airborne chemical pollutants, increased ultraviolet radiation from ozone depletion, cattle grazing, pathogens, and drought.
POPULATION TREND: The Yosemite toad was historically abundant in the high country of the central Sierra Nevada, but by the early 1990s had been eliminated from about 50 to 69 percent of known historical sites. Many known large populations of toads have recently crashed by up to 99 percent or disappeared completely. Declines of the toad have been especially alarming in Yosemite National Park, with recent studies at Tioga Pass documenting wholesale population crashes. In 1915, biologists found the Yosemite toad to be “numerous” and “abundant” at many locations in the park, but a re-survey in 1992 found that toads had disappeared from 50 percent of historic Yosemite locations.
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