What Do Bullfrogs Sound Like?
The American bullfrog call is one of the most recognizable in the United States. The most common bullfrog sound is the male’s mating, or “advertisement”, call. This sound resembles a booming “vaarrhummm!” or “jug-o-rum!” that echoes across ponds or lakes during the breeding season in late spring and summer.
American bullfrog (Lithobates catesbeianus) calls are one of about 30 true frog calls in the United States and one of about 100 frog and toad calls.
For me, the calls of bullfrog bring back childhood memories of being out in nature at dusk, enjoying the quiet and solitude that comes with a summer evening beside a favored pond.
The video below is a fantastic example of this noise, and it allows you to see how the frog’s throat expands to produce such a loud sound.
How Do Bullfrogs Call?
The American bullfrog call is produced by the contraction of the frog’s vocal sac. This sac is a large, expandable pouch located in the throat of the frog that is used to amplify its voice.
When the male bullfrog wants to call, it will fill its lungs with air and then push the air out through its vocal cords and into the vocal sac. The sac will then expand, creating a deep, resonant sound.
Why Do Bullfrogs Call?
The the most common bullfrog call is generated by male frogs to attract females during mating season. However, calls – and other noises – can be used to establish the bounds of its territory and challenge rival males. Females also sometimes call to demarcate territory, and both sexes also have alarm and distress calls.
Mating Calls
Mating (or “advertisement”) calls, composed of between 3 and 15 rising and falling notes in rapid succession, are the most familiar to most people.
These are the sounds of bullfrogs that you’ll most often hear during the spring and summer months around ponds and lakes. Because bullfrogs have an extended mating season – typically several months – you will often hear them calling for much of the summer.
During bullfrog mating calls, the male inflates its paired vocal sacs. Individual notes last 0.6-1.5 seconds, with intervals between notes of 0.5-1.0 seconds.
Interestingly, there is an inverse relationship between the size of the male and the resonance of his mating call. This means that the call transmits information to the female about his potential as a mate as well as his location.
Territorial Calls
Both male and female bullfrogs use territorial calls to establish the bounds of their territories to members of their own sex. The male’s territorial call challenges nearby or rival males and asserts ownership of the territory. These characteristics of these sounds vary more than mating calls, but they tend to be much shorter (and much more difficult to identify).
If the territorial call is unheeded by an approaching frog, an attack may follow. A female bullfrog’s territorial call serves the same function.
Bullfrogs stake out their patch of pond – usually and area of shoreline between 6 and 20 feet – and defend it with vigor; they are among the most aggressive species of frogs.
Alarm, Distress, and Release Calls
Bullfrogs will sometimes use an alarm call as they leap into the water to escape a potential predator. It tends to be a much higher pitch and much shorter than the mating call. This sound is intended to startle the predator and warn other frogs. I’ve most often heard type of call when I suddenly come upon a frog when walking along the shore of a pond, just before it dives beneath the surface. .
If a bullfrog is caught by a predator or even held by a person, it may emit a distress call — a loud scream. Unlike other calls, the scream is produced with the mouth open.
Finally, when a male frog is accidentally clasped by another male while in the midst of the breeding pool, it will croak or chirp to signal that it should be released.
Where Can I Hear Bullfrogs?
Bullfrogs can be found throughout much of the United States. The map below shows their native range in orange, and introduced or non-native range in red.
References
Sources consulted for this page include the following:
Dodd, C. Kenneth (2013). Frogs and Toads of the United States and Canada (Second Edition). The John Hopkins University Press, Baltimore.
“Lithobates catesbeianus (American Bullfrog)”. Animaldiversity.org.
“Sounds of American Bullfrog – Lithobates catesbeianus“. Californiaherps.com