In recent weeks, a friend of mine living in Emerald in Whistler has had her sleep (not to mention other activities) seriously disrupted by the nightly chorus of amphibians in her local wetland. The Sea to Sky corridor is home to four species of frogs and one species of toad.
The Columbia Spotted frog ( Rana luteiventris ) can be up to 10 cm in length, with females slightly larger than males. This dimorphism is common in most frog and toad species.
Another dimorphism in most species is that only the males are vocal; the male Columbia Spotted frogs call is a weak 5-10 beat cluck, similar to the sound of a human clicking their tongue against the roof of their mouth.
The Wood frog ( Rana sylvatica ) can grow up to 5 cm in length, with the males sounds very much like the quack of a duck. The Pacific treefrog ( Hyla regilla ) is up to 4 cm long. The mating call of the male is a loud krek-ek sound. Lastly the Coast Tailed Frog (Ascaphus truei) is only 3.5 cm from nose to rump and both sexes of this species are voiceless.
The only toad in our area is the Western toad ( Bufo boreas ) with a length of up to 14 cm. Most toads, the Western toad included, have a kidney-shaped parotid gland behind each eye. This gland along with its warts, if it has them, is used to secrete a bitter, sticky substance to ward off predators. The male Western toad does not produce a mating call, but will emit a quiet, twittering release call if they are accidentally grasped by another male during courtship.
The breeding seasons for our local frog and toad species occur sometime between February and June, the exception being the Coast Tailed frog who mates in the autumn. Most species of male frogs and toads have a distinct call to attract females of their species to the breeding area. The breeding area is usually the edge of a small, slow moving body of water or a wetland.
The male produces sound by passing the air from his lungs over the vocal chords to the vocal sacs. The vocal sacs act as resonators, amplifying the sound proportionally to their size. The vocal sacs of the Pacific treefrog amplify their call so loudly they can be heard up to 1.5 km away, whereas the Columbia Spotted frogs call travels only 30 metres.
The male frogs and/or toads calling within a particular wetland create what is called a "chorus". The chorus usually occurs at night to avoid predation, but males will call during the day at the peak of the breeding season. The males can sense vibrations in the water created by approaching females, predators or even a strong breeze. These vibrations can cause individuals or even the entire chorus to stop calling while they determine what created it. When the frogs/toads are sure there is no threat they will begin calling/chorusing again.
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