American Bullfrog (Lithobates catesbeianus) are non-native species to Whatcom County. They are identifiable by their large eardrums (tympanum), dorsolateral fold that bends around the eardrums, and large bodies. American Bullfrogs have several different types of calls, but for call surveys, we will primarily be hearing their mating call or territorial calls. Alarm calls might be heard if you’re approaching their habitat. Mating calls of American Bullfrogs are identified by low baritone chorusing “jug-o-rum“.
Green Frogs (Lithobates clamitans) are also non-native and also have large tympanums like the bullfrog, but they have dorsolateral folds that extend down their back and are generally smaller than American Bullfrogs. Green Frog mating call resembles a banjo-like twang usually given in a row as a “GUNK! Gunk! gunk.” When startled, only the American Bullfrog makes a high pitched chirp followed by a splash as they dive into the water.
Green Frog and Bullfrog tadpoles look similar, but may be distinguished by the spotting pattern on their tail fin. Green Frog (right) has a more speckled pattern. In comparison, Bullfrogs (left) have more distinct spots. Both species lay their egg mass in large sheets that float on water surface and vegetation.
The video below shows an American Bullfrog making advertisement or mating calls with the other bullfrogs. Once in a while he’ll make the single brmmp! territorial call as he turns away. In the background, you can also here the advertisement calls of Green Frogs.
A video of a green frog calling and another one in the background.
More resources available to get familiar with American Bullfrog and Green Frog mating calls:
http://musicofnature.com/calls-of-frogs-and-toads-of-the-northeast/ (has a great sound clip of various types of calls with descriptions)