In February, 2000, environmental groups submitted formal petitions with the U.S. Fish and Wildlife Service (USFWS) to protect the Yosemite under the Endangered Species Act. In late 2002 the USFWS concluded that it warrants protection under the Endangered Species Act. Unfortunately, the Service noted that budgetary constraints precluded them from listing the toad as threatened or endangered at the time. This decision was followed by more legal action seeking to force the Service from the delay in designating endangered status to the Yosemite toad. As of 2007, this imperiled species is still not listed under the Endangered Species Act and has also lost the proactive conservation measures prescribed in the original Sierra Nevada Framework following the revisions to that plan in 2004. It is currently a Forest Service Sensitive Species and a California State Species of Special Concern.
From 2005 to 2010, the research team conducted experiments on 39 meadows in the Sierra National Forest, analyzing the effects of different management practices including grazing across the entire meadow, fencing to exclude livestock from breeding areas and no grazing within a meadow. They examined the impact of these practices on tadpole density, breeding-pool occupancy, water quality and other elements that support Yosemite toad survival.
Livestock grazing is apparently not the culprit in the steep decline of Yosemite toads and their habitat, according to the results of an extensive, five-year study conducted by UC Davis, UC Berkeley and the U.S. Forest Service.
“A direct correlation between the intensity of cattle use and toad occupancy of meadows was not found for any portion of the grazing season — early, mid or late,” said Leslie Roche, a UC Davis Department of Plant Sciences graduate student who worked on the study.
It has been estimated from population studies that the Yosemite Toad has disappeared from over 50% of its historic range, even in habitats that still appear to be unaltered. Remaining populations may not be reproducing enough to survive. One population at Tioga Pass, counted for more than 20 years, had declined by 90 percent in 1993.
The causes of the decline are unclear. Disease, degradation of habitat by grazing livestock, increased ultraviolet radiation, introduced predatory fishes, a severe 1980's drought, windborne pesticide contamination, and increased predation by Common Ravens, whose population has increasd greatly due to human activities, are all causes which are thought to have contributed to the decline.
An advertisement call is the most well-known call of a toad. It is produced by a male during the breeding season to attract females of his own species. It can also serve an agressive function to defend his calling site by warning rival males of his presence. Toads usually make the calls around bodies of water that are suitable for breeding and egg laying. These calls can be heard during the evening and at night, and sometimes during daylight at the peak of the breeding season.
The advertisement call of the Yosemite Toad is a long, rapid musical trill, repeated at frequent intervals. It is produced by a male to attract females during the breeding season and to warn other rival males of his presence. It seems to vary in pitch and speed among toads, and this might be due to temperature.
Reproduction: Mating occurs between April and July. Unlike the mountain yellowlegged frog, these tadpoles only need a few months to develop into young adults. These toads can be seen hopping across the snow in early spring as they are returning to water in hopes of mating. Due to their short growing season, the sooner they lay their eggs in the water, the sooner their eggs can develop into young adults before it snows again.
Distribution and Habitat:
Yosemite toads ( Bufo canorus ) are endemic to the Sierra Nevada, California, from Ebbetts Pass, Alpine County to the Spanish Mountain area, Fresno County (Karlstrom, 1962, 1973; Stebbins 1966; unpublished Sierra National Forest survey data, 1995, 2002). Sites occur from 1,950–3,444 m elevation, with the majority of sites between 2,590–3,048 m (Karlstrom, 1962). Jennings and Hayes (1994a) estimate that populations have disappeared from 50% of historically reported sites, although the overall range of the species may have only contracted in the far north and in western Fresno County. Disappearances have been concentrated at lower elevation sites on the western edge of the range, with greater persistence at higher elevation sites (Davidson et al., 2002).
Active in daytime, usually in sunny areas. Activity period is relatively short, from April - July, to late September or early October. After breeding, males and females move from the breeding pond into meadows where they feed for 2 - 3 months before the snows return.
During winter, Yosemite Toads shelter in rodent burrows, willow thickets, forest edges adjoining meadows, and in clumps of vegetation near water.
Like most toads, this one is slow moving, often using a walking or crawling motion along with short hops.
Calling males at breeding sites will defend their territory from other males.
For defense, Yosemite toads rely on parotoid glands and warts which can secrete a poison that deters some predators.
Diet consists of a wide variety of invertebrates, including beetles, ants, siders, bees, wasps, flies, and millipedes. The prey is located by vision, then the toad lunges with a large sticky tongue to catch the prey and bring it into the mouth to eat.
Adults are 1 3/4 - 2 3/4 inches from snout to vent ( 4.4 - 7 cm).
Robust and stocky with dry, uniformly warty skin. No cranial crests. Large, flat oval paratoid glands. Eyes are closely set, pupils are horizontal. Dorsal stripe is very faint or absent. Sexes are colored differently. Males are pale yellowish green or olive above, with few or no dark blotches. Females and young are heavily blotched on a light background. Throat and belly is pale on both sexes.
Kingdom: Animalia; Class: Amphibia; Order: Anura; Family: Bufonidae