The loud, rhythmic chorus of frogs near a pond is one of nature’s most familiar sounds, and males are widely understood to be responsible for this nightly performance. For decades, bioacoustics focused primarily on these dominant male vocalizations, painting female frogs as the silent partners in the amphibian world. This perception arose because male calls are louder, longer, and more frequent, making them easier to study. However, scientific observation reveals that female frogs are far from silent, possessing a repertoire of chirps, clicks, and croaks used for specialized communication. Ongoing research explores the behavioral necessity and underlying biological structures responsible for the sounds female frogs produce.
The Primary Role of Male Vocalizations
A frog chorus serves a clear biological function: to advertise the male’s presence and quality to potential mates. These advertisement calls, the classic croak or trill, are species-specific sounds broadcast over long distances to attract females to the breeding site. The acoustic properties of these calls are genetically encoded and signal a male’s fitness. Females often prefer calls that are longer or lower in frequency, which correlates with a larger body size.
Male vocalizations also function in competition, establishing a social hierarchy within the breeding chorus. Territorial calls, sometimes called aggressive calls, are distinct sounds used to warn other males to maintain distance from an established calling spot. Rival males may respond with their own calls or physical confrontation. A third type, the courtship call, is a quieter sound produced at close range, serving as a final persuasive signal before amplexus, the mating embrace.
Specific Noise Production in Female Frogs
Female frogs utilize vocalizations for several specific communicative purposes, though their sounds are softer and less frequent than those of males. The most common female vocalization is the release call, a short, simple sound made when a female is mistakenly clasped by a male. This sound signals that the female is unreceptive, already carrying fertilized eggs, or is another male, prompting the clasper to disengage. The release call prevents wasted energy and potential injury from incorrect mating attempts.
Females also produce distress calls, which are loud, sharp screams emitted when the frog is under attack or physically handled. This call may serve to startle the attacker, allowing the frog a chance to escape, or it may alert other potential predators to the struggle. In a few species, females also exhibit aggressive calls, typically occurring during competition for resources or prime locations.
A rarer, but significant, form of female vocalization is the true mating or advertisement call, which directly attracts a male. In the smooth guardian frog (Limnonectes palavanensis), for example, females call spontaneously and more frequently than males. The concave-eared torrent frog (Odorrana tormota) is another unusual example, where females emit short, high-frequency ultrasonic calls that guide males to them in their noisy, fast-flowing stream habitat. These specialized reproductive calls often occur in species with unique mating systems, such as sex-role reversal, where the female actively seeks and competes for the male.
The Anatomy of Frog Sound Production
The fundamental mechanism for sound production is shared by both male and female frogs, involving the controlled movement of air over the vocal cords within the larynx. The larynx, or voice box, contains the vocal cords, which are folds of tissue that vibrate as air from the lungs passes across them. This vibration creates the initial sound pulse, the source of all frog calls.
The difference in sound volume and duration between the sexes is due to the presence of the vocal sac, a structure that is absent or significantly reduced in most females. The vocal sac is a pouch of skin that inflates with air channeled from the lungs. This sac acts as a highly efficient resonator and amplifier, allowing males to produce loud, sustained croaks that carry over long distances.
Since female frogs typically lack this large, resonating sac, their calls are quiet, short, and non-amplified, often sounding like a muffled chirp or click. In species like the spring peeper, the muscles responsible for vocalization make up about 15% of the male’s body mass but only around 3% of the female’s. These anatomical differences explain why female calls are mainly reserved for close-range communication or immediate distress.