Boreal Toad
Boreal Toad
Anaxyrus boreas boreas
Anaxyrus boreas boreas
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Population, Conservation Status, Threats:
Considered endangered in Colorado, boreal toad populations are in steep decline across their range. They are threatened by many factors, including habitat loss and pollution, habitat fragmentation, and the chytrid fungus.
Physical Description:
Boreal toads are brown-gray in color, with dark blotches across the entirety of their body, and a light stripe running down their back. Immature toadlets are completely black.
Overall range of the boreal toad and the California toad from CaliforniaHerps. Boreal toad range is shown in red - in Colorado, they are only found in portions of the Rocky Mountains.
Habitat:
Boreal toads are the only alpine toad in Colorado, found at elevations from 7,000 to 12,000 feet. Toads prefer bodies of slow or still water with large shallow areas for breeding, and are a species that benefits greatly from beaver-made ponds and marshes. Adult toads spend their time both in damp marshland areas and at the margins of bodies of water, and in upland spruce-fir forests and alpine meadows, while young are entirely aquatic.
Behavior:
Boreal toads spend over half the year hibernating underground. Unlike most toad species, boreal toads lack vocal sacs and are unable to produce loud mating calls, instead vocalizing only with soft chirps and squeaks. Their primary defense against predators is the poison glands just behind their head, which can produce a noxious toxin.
Diet:
While tadpoles are omnivorous, consuming aquatic plants, carrion, and small animal prey, adult toads are strictly predatory; they prey almost exclusively on invertebrates, both aquatic and terrestrial.
Reproduction:
Depending on altitude, breeding may take place in late spring to mid-to-late summer. Females may not breed every year. When breeding does take place, females lay an average of 5,000 eggs per clutch in shallow water. Eggs will hatch in 3-10 days, and tadpole development is highly dependent on temperature - in cold locations, it can take over a month for tadpoles to metamorphose. Individuals reach sexual maturity at 4-6 years of age.
Associated Species:
Batrachochytrium dendrobatidis, or the chytrid fungus, is a concerning threat to amphibian populations worldwide, including boreal toad populations; the fungus infects skin and keratinized portions of the body, causing hyperplasia and ulcers, and kills by compromising electrolyte balance and osmotic regulation, eventually causing cardiac arrest. Boreal toads are often found in beaver ponds, which make for good habitat and spawning sites. Some animals like ravens have learned to predate upon them despite their toxicity, by learning to avoid their poison-producing glands while hunting and feeding.
Illustration by Willow Sedam
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