Tuesday 18 June
Boreal toad (Anaxyrus boreas)
Boreal toad fact file
- Find out more
- Print factsheet
Boreal toad description
A large, robust amphibian of western North America, the boreal toad (Anaxyrus boreas) has thick, dry skin that is covered in dark or rusty blotches (1) (3). Variable in colour, the boreal toad has a mixture of green, tan, reddish-brown, dusky gray, and yellow on the upperparts (3), while the underparts tend to be pale with black mottling (4). There is also a pale stripe down the middle of the back, and the throat is pale (3) (4).
The boreal toad has a stocky body, with short legs, and tends to walk rather than hop. The head is wide, with a prominent kidney-shaped swelling called a ‘parotoid gland’ behind the large eyes. The eyes are beautifully flecked with gold and have distinctive horizontal pupils (4). The male boreal toad is generally smaller than the female,and has less blotched, smoother skin (3). The male also has dark pads on the thumbs that help it cling to the female during mating (4).
Unlike many other toads, the male boreal toad has no vocal sac and, therefore, no mating call. However, males are known to emit a chirping sound when distressed, when clasped by other males, or when gathered in breeding aggregations. Females will also emit a chirping sound, but are usually silent (2).
There are currently two recognised subspecies of the boreal toad: the California toad, Anaxyrus boreas halophilus, and the nominate, Anaxyrus boreas boreas. Anaxyrus boreas boreas generally has more dark blotches on the belly than the California toad, as well as a wider head, larger eyes and smaller feet (3).
- Also known as
- California toad, western toad.
- Bufo boreas, Bufo politus.
- Female snout-vent length: c. 11 cm (2)
- Male snout-vent length: c. 9.5 cm (2)
- Tadpole head-body length: 1.4 - 1.7 cm (2)
- Tadpole tail length: 1.6 - 2 cm (2)
IUCN Amphibian Specialist Group:
- Simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
- The flesh of a dead animal.
- Litter formed from fragments of dead material.
- An organ that makes and secretes substances used by the body.
- A winter survival strategy in which the animal passes the winter in a resting state. This period of inactivity is characterised by specific biological and biochemical changes including lowered blood pressure and respiration rate.
- Animals with no backbone, such as insects, worms, spiders and corals.
- An abrupt physical change from the larval to the adult form.
- Nominate subspecies
- The subspecies indicated by the repetition of the specific name.
IUCN Red List (May, 2011)
- U.S. Fish & Wildlife Service (2004) Species Assessment and Listing Priority Form. U.S. Fish & Wildlife Service, U.S.
CaliforniaHerps.com - Anaxyrus boreas halophilus (May, 2011)
Government of British Columbia - Western toad (May, 2011)
Colorado Division of Wildlife - boreal toad (May, 2011)
- view the contents of, and Material on, the website;
- download and retain copies of the Material on their personal systems in digital form in low resolution for their own personal use;
- teachers, lecturers and students may incorporate the Material in their educational material (including, but not limited to, their lesson plans, presentations, worksheets and projects) in hard copy and digital format for use within a registered educational establishment, provided that the integrity of the Material is maintained and that copyright ownership and authorship is appropriately acknowledged by the End User.
Boreal toad biology
Active by night and day, the boreal toad seeks out its invertebrate prey by moving slowly across the ground (3). The boreal toad locates its prey using its excellent vision, and then lunges its large sticky tongue to catch the target and bring it to its mouth to eat. Boreal toad tadpoles consume algae and detritus, including fish carrion (3).
For defence, the boreal toad relies on its paratoid glands and warts, which secrete a poison that deters predators. As a result, many predators have learned to avoid the boreal toad to prevent them ingesting this poison. However, some other predators have learnt to only consume edible body parts; ravens, for example, only eat the internal organs (3).
The boreal toad hibernates through winter months. In mountainous regions, it emerges from its burrow refuge when the snow has melted and the temperature during the day remains above freezing. Breeding begins soon after it emerges, occurring in July or August at higher altitudes, but as early as May at lower altitudes (2). The male boreal toad arrives at the breeding sites first, using scent cues to find its way (3). It soon initiates breeding by vigorously pursuing and clasping receptive females (2). Mating takes place in water and during amplexus (the mating embrace), the mating male will kick away other males, occasionally even engaging in brief fights (3). The female boreal toad lays 2 strings of up to 16,500 eggs in shallow water (2). The eggs contain some of the adult boreal toad’s toxins, which offers some protection from predation, and the eggs hatch after three to ten days (3).
Tadpole development is highly dependent on water temperature, and the tadpoles may enter metamorphosis as early as 30 days after hatching in warm water (3), but may take as long as 75 days in cold water (2). During metamorphosis, the tadpoles aggregate in shallow water. Newly-transformed boreal toads often spend the winter at the border of the wetland in which they hatched, although they may disperse to nearby sites. The boreal toad may live for up to nine years (3).Top
Boreal toad range
The boreal toad occurs throughout much of the mountainous areas and along the Pacific coastline of the western United States (2). It ranges from southern Alaska south to Baja California, and eastward to the Rocky Mountains in west-central Alberta, Montana, Wyoming, Utah and Colorado. It formerly occurred in northern New Mexico, but is now thought to be extinct at this location (1).
The California toad ranges throughout most of California, from the northern forests, east into west-central Nevada, and south through most of the state, east of the deserts, into northern Baja California (3).Top
Boreal toad habitat
Occupying a great variety of habitats, the boreal toad may be found around desert springs, meadows, woodlands and mountain wetlands, as well as ponds, lakes, reservoirs, and slow-moving rivers and streams (1) (3). During the breeding season the boreal toad is most commonly found near permanent or temporary water bodies that have shallow sandy bottoms, while after breeding it disperses into terrestrial habitats, such as forests and grasslands. Even when it roams far from water, the boreal toad prefers moist conditions (4). This species is found at elevations between sea level and around 3,640 metres (1).Top
Boreal toad status
The boreal toad is classified as Near Threatened (NT) on the IUCN Red List (1).Top
Boreal toad threats
The boreal toad population has undergone a drastic decline, disappearing completely from many parts of its range. A number of threats to the boreal toad have been identified, yet the exact cause of this decline, as well as the significance of each threat, is currently poorly understood. The Rocky Mountain populations in Colorado and Wyoming have undergone a drastic decline since the 1970s. Populations of the boreal toad have also declined greatly in the Yosemite area of the Sierra Nevada, while this species is also undergoing localised declines in Yellowstone National Park, Montana (1).
One of the greatest threats to the boreal toad is thought to be habitat destruction and degradation (1). Development in and around wetlands can destroy or isolate populations, while traffic on roads can kill migrating toads (3). The pollution and introduction of aquatic predators, such as fish stocking in lakes, also degrades this species’ habitat, as well as causing increased mortality and the greater likelihood of the spread of disease (4). In the Cascade Range of Oregon, predation by ravens during the toad breeding season appears to have contributed significantly to some population declines, while significant predation by birds has also been observed in Colorado and Idaho (1).
Another threat to the boreal toad is the chytrid fungus, which may have been the cause of mass deaths in the southern Rockies. This threat is likely to increase in significance with global climate change, which will create the ideal conditions for the spread of this deadly disease (1) (4).Top
Boreal toad conservation
The boreal toad is afforded sanctuary in a number of national parks, wildlife refuges, and wilderness areas in the U.S, where its habitat is protected. In Mexico, its habitat is also protected by the Parque Nacional Sierra de San Pedro Martir (1).
The alarming decline of the boreal toad has prompted a large amount of conservation action. In some areas, monitoring programmes have been implemented, while surveys have been conducted to identify breeding sites and assess the habitat requirements of this species (4). Other research has focused on developing methodologies for reintroducing the boreal toad to areas where it formerly occurred, as well as refining husbandry practices for captive toads and ways to detect the chytrid fungus in the wild (5).Top
Find out more
For more information on amphibian conservation:
This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
More »Related species
Play the Team WILD game
MyARKive offers the scrapbook feature to signed-up members, allowing you to organize your favourite ARKive images and videos and share them with friends.
Terms and Conditions of Use of Materials
Copyright in this website and materials contained on this website (Material) belongs to Wildscreen or its licensors.
Visitors to this website (End Users) are entitled to:
End Users shall not copy or otherwise extract, alter or manipulate Material other than as permitted in these Terms and Conditions of Use of Materials.
Additional use of flagged material
Green flagged material
Certain Material on this website (Licence 4 Material) displays a green flag next to the Material and is available for not-for-profit conservation or educational use. This material may be used by End Users, who are individuals or organisations that are in our opinion not-for-profit, for their not-for-profit conservation or not-for-profit educational purposes. Low resolution, watermarked images may be copied from this website by such End Users for such purposes. If you require high resolution or non-watermarked versions of the Material, please contact Wildscreen with details of your proposed use.
Creative commons material
Certain Material on this website has been licensed to Wildscreen under a Creative Commons Licence. These images are clearly marked with the Creative Commons buttons and may be used by End Users only in the way allowed by the specific Creative Commons Licence under which they have been submitted. Please see http://creativecommons.org for details.
Any other use
Please contact the copyright owners directly (copyright and contact details are shown for each media item) to negotiate terms and conditions for any use of Material other than those expressly permitted above. Please note that many of the contributors to ARKive are commercial operators and may request a fee for such use.
Save as permitted above, no person or organisation is permitted to incorporate any copyright material from this website into any other work or publication in any format (this includes but is not limited to: websites, Apps, CDs, DVDs, intranets, extranets, signage, digital communications or on printed materials for external or other distribution). Use of the Material for promotional, administrative or for-profit purposes is not permitted.