This species occurs along the Pacific Coast of North America from southern Alaska (Wiedmer and Hodge 1996) to Baja California in Mexico, and ranges eastward through the Rocky Mountains in west-central Alberta, Montana, Wyoming, Utah (Ross et al. 1995) and Colorado (Hammerson 1999), to northern New Mexico (COSEWIC 2012). It is absent from most of the desert south-west (Stebbins 2003). Its elevational range extends from sea level to at least 3,640 meters.
Habitat and Ecology
This species is found in a wide variety of habitats including desert springs and streams, meadows, marshes, woodland, mountain wetlands and agricultural land. It is also known from around ponds, lakes, reservoirs, and slow-moving rivers and streams. It digs its own burrow in loose soil or uses those of small mammals, or shelters under logs or rocks. The eggs and larvae develop in shallow areas of ponds, lakes, or reservoirs, or in pools of slow-moving streams. The toads undertake seasonal migrations to and from breeding sites; newly metamorphosed young form large aggregations and migrate en masse to upland foraging areas.This species exhibits breeding site fidelity (COSEWIC 2012). Adult males in Alberta and a portion of northwestern Montana are unique in possessing a vocal sac and producing a loud advertisement call, while males from other parts of the range lack this structure and a true advertisement call (Pauly 2008).
The total adult population size of the species is unknown but surely exceeds 100,000. Although this species remains common throughout much of its range, many known sites have experienced population declines. The Rocky Mountain populations in Colorado and Wyoming underwent a drastic decline between the 1970s and 1990s (Corn et al. 1989; Hammerson 1989, 1992, 1999; Carey 1993; Muths et al. 2003). The species has also declined greatly in the Yosemite area of the Sierra Nevada, California (Drost and Fellers 1996), and has declined in Yellowstone National Park (Peterson et al. 1992) and Montana (Reichel and Flath 1995). Declines have been observed in southwestern British Columbia, but the species remains widespread within the northern portion of its range in the province (COSEWIC 2012). Overall, the recent and current rate of decline is unlikely to exceed or come close to 30 percent over 10 years or three generations.
Die-offs in the southern Rockies have been associated with chytrid fungus (
This species occurs in many national parks, wildlife refuges, and wilderness areas where habitat destruction is not a major threat (but pathogen-related declines may still occur). In Mexico, this species occurs in San Pedro Martir National Park, and Valle de los Cirios Protected Area. In Canada, it is listed as Special Concern under the federal Species At Risk Act. The taxonomic status of the various regional populations of this species is in need of further study.
IUCN SSC Amphibian Specialist Group 2015. Anaxyrus boreas. In: IUCN 2014