Tree frogs are amphibians known for their ability to climb and their prominent presence in nighttime choruses. These creatures are instantly recognizable by their distinct vocalizations, which are a familiar sound in many environments. The loud, persistent croaking heard near ponds is overwhelmingly produced by males. This raises the question of whether female tree frogs also vocalize and how their sounds differ.
The Purpose of the Male Croak
The loud, sustained croaking that defines a frog chorus is the advertisement call, central to the male’s reproductive strategy. This vocalization is primarily a mating call, intended to attract receptive females over long distances. The call’s intensity indicates the male’s fitness, with females often preferring deeper calls that suggest a larger body size.
The advertisement call also serves a dual purpose in species recognition, since each frog species possesses a distinct “love song.” This ensures that females, whose ears are tuned to their species’ frequency, approach the correct mate. Male tree frogs also use aggressive or territorial calls to warn off competitors and defend their chosen calling site, helping space out rival males.
When and Why Female Tree Frogs Vocalize
Female tree frogs possess the anatomical ability to produce sound, but their vocalizations are quieter, less frequent, and serve distinct social functions. One specific sound is the reciprocal call, a rare, soft response a female may emit after hearing a male’s croak. This signal indicates she is receptive and ready to approach the male for mating.
Another important sound is the release call, a soft vibration made when a female is mistakenly clasped by an overzealous male. This call, made by both sexes, signals that the clasped frog is not a potential mate, such as a gravid female or another male. The call encourages the amorous male to let go and conserve his energy.
Both male and female tree frogs produce a loud, sharp distress call when physically threatened or attacked by a predator. This sound is often described as a sudden “scream” or a single “bwak” that can startle a potential threat, offering a brief moment for the frog to escape. Unlike other calls, the distress call is often produced with the mouth open, changing its acoustic properties. Female vocalizations are used for immediate, close-range social or defensive interactions.
How Tree Frogs Produce Sound
The physical mechanism for sound production is fundamentally the same in all tree frogs, relying on the passage of air across specialized structures. Sound is generated in the larynx, or voice box, where air causes the vocal cords to vibrate. The initial vibrations are then modified and amplified.
The air used for calling cycles back and forth between the lungs and the vocal sac, rather than exiting the mouth or nostrils. This air-recycling system allows the frog to produce sustained, repetitive calls without stopping to breathe. The vocal sac, a flexible pouch beneath the chin, acts as a resonating chamber to amplify the sound. This structure is much more developed in males, which is why their calls are significantly louder and carry further.