About Anaxyrus canorus (Camp, 1916)
The Yosemite toad, scientifically named Anaxyrus canorus, formerly classified as Bufo canorus, is a true toad species belonging to the family Bufonidae. This species is endemic to California’s Sierra Nevada, with a range extending from Alpine County to Fresno County. Yosemite toads only occur in the montane to subalpine elevational zone, between 1,950–3,445 m (6,398–11,302 ft) above sea level. It resembles the closely related nearby western toad, Anaxyrus boreas, but has a range of adaptations suited to a high elevation lifestyle. It was first described by Charles Camp, an undergraduate student of Joseph Grinnell, during the Grinnell Survey of California. Yosemite toads primarily use montane and subalpine wet meadows as breeding habitat, though they will occasionally breed in ephemeral ponds, lake margins, and other riparian areas. The species tends to favor flatter, southwesterly meadows that receive more precipitation and hold warmer water. Breeding specifically occurs in shallow snowmelt ponds or flooded areas, with eggs usually laid in water less than 5 cm deep. This shallow water puts eggs at risk of freezing, due to the very low nighttime temperatures during spring snow melt. Female Yosemite toads sometimes split their egg clutches between multiple areas, or lay their clutches communally alongside other breeding pairs in a single spot. Researchers think the relatively high amount of pigment in Yosemite toad eggs and tadpoles helps speed up development. During the day, tadpoles gather in the shallowest, warmest margins of their ponds. At night, tadpoles settle into silty detritus, which insulates them from cold nighttime temperatures. This behavior leaves small divots in the silt, often giving breeding pools a textured appearance described as resembling golf balls. Many breeding ponds dry out completely each season before tadpoles can complete metamorphosis, creating an apparent selective tradeoff: shallow ponds speed up tadpole development, while longer-lasting ponds support higher survival rates. The period from hatching to full tadpole metamorphosis lasts 4–6 weeks, and this timeline is heavily influenced by environmental factors including elevation, weather, food availability and competition, and may also be affected by genetic background. Tadpoles cannot survive overwintering. Habitat use patterns of subadult and adult Yosemite toads remain poorly understood. Newly metamorphosed toads leave breeding ponds soon after transformation, and most likely overwinter nearby in stream channels and associated vegetation like willows, sedges, and grasses. Most juveniles at one year of age or older disperse further upland into adult foraging habitat by mid-summer of their second year, though some can still be found near breeding ponds. Adult upland foraging habitat is typically characterized by seeps and springs, willows, tall forbs, granitic boulders, or forest clearings at lower elevations. Rodent burrows provide essential shelter from predators and harsh weather, alongside willows, logs, and rocks. For overwintering, Yosemite toads use rodent burrows built by species such as pocket gophers, voles, and Belding's ground squirrels, as well as tangled willow roots. These sites maintain the optimal thermal and moist conditions hibernating toads need.
