Male frogs have tremendously diverse vocalizations, and their sounds can mean different things depending on the listener. Female frogs might assess the quality of a male through the nuances of his call. Male frogs might decide whether or not to fight based on a the sound of another male's call. Predators might think the song signals a tasty treat. People might interpret the songs as a sign of the change of seasons.
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American Toads (Bufo americanus A.K.A. Anaxyrus americanus) have high pitched trill that can last from six to twelve or more seconds. Its long duration helps distinguish it from the individual "Peeps!" of the Spring Peeper, or the short trill of the Gray Treefrog.
American Toad 2015 Playlist: four short videos of American Toad breeding behavior. The first video shows two toads calling to each other. The second video shows a toad calling next to a spring peeper. The third video shows some male toads trying to break apart two amplexed pairs of toads. The fourth video shows a group of four males battling each other to mate with a single female toad.
American Toad 2016 Playlist: several short videos of American Toads in northeast Ohio. The first set of videos show individual calling male toads before females arrive at the pond. In addition to the long trill of the toads, you can hear the Spring Peepers calling too.
Spring Peepers (Pseudacris crucifer) have a distinctive call that consists of a single high-pitched "Peep!". Individual Spring Peepers can make these peeps in quick succession. When hundreds of Spring Peepers are gathered together on a warm rainy night during the breeding season, the sound can be deafening!
This video shows a complication of observations from Michigan in 2010. It starts with a view of a pond at sunset; peepers can be heard around the pond. Then a view of a spring peeper calling is shown. At 24 seconds into the video, a head-on shot of a spring peeper is shown. At 35 seconds, there is a view of a a male and female spring peeper in amplexus. The video ends with another view of a calling male spring peeper.
Many hypotheses have been proposed for why frogs have evolved large vocal sacs. One hypothesis is that the pulsating vocal sac serves as a visual signal to attract females. The head-on video of the calling male peeper at 24 seconds seems suggestive of a visual signal.
The video to the left shows a top-down view of a calling male pacific chorus frog. This video provides a nice visual illustration of another function of the vocal sac: to refill the lungs after calling. As you watch the video, you can see the relationship between the vocal sac and the lungs. Sound is produced as the frog forces air out of its lungs into the vocal sac. The air rushing out of the lungs passes through the vocal cords, creating the frog call. As the lungs deflate, the body appears to get smaller as the vocal sac expands. But after the frog is done calling, the air is forced from the vocal sac back into the lungs. You can see this happen as the vocal sac gets smaller and the frog's body appears to get larger as it fills with air.