The sounds produced by toads are often generically referred to as “chirps,” but scientists describe their vocalizations more accurately as croaks, trills, or sustained buzzes. These calls form a complex acoustic communication system used by toads and other anurans. Vocalization is a primary method for species to announce their presence, locate one another, and exchange information, which is fundamental to a toad’s social organization, especially during the breeding season.
The Primary Purpose of the Call
The most frequent and recognizable toad vocalization is the advertisement call, which serves as the central function of sound production. Only male toads produce these loud, sustained calls to advertise their location and mating readiness to potential female partners. The advertisement call is species-specific, allowing females to locate and identify a male of the correct species, even within a noisy chorus of multiple toads calling at once.
Female toads are highly selective, using the quality of the male’s call as an indicator of his physical condition and genetic value. A longer call duration, a higher call rate, or a lower frequency pitch can signal greater body size and endurance. The energy required to sustain a long, loud call is significant, making it an honest signal of a male’s fitness.
The advertisement call also acts as a mechanism for spacing out competing males and defending a calling site. When a rival male encroaches on a territory, the resident male often switches to a more aggressive call, typically a shorter, stuttering trill or croak. This “encounter call” allows males to assert dominance and maintain an optimal distance from competitors without resorting to physical conflict. This prevents unnecessary energy expenditure in fights, ensuring the male can continue attracting a female.
How Toads Create Sound
The physical mechanism for sound production centers around the larynx, which houses the vocal cords, and the vocal sac, an elastic pouch of skin located under the throat. A toad initiates a call by contracting the muscles around its lungs, forcing air across the vocal cords. The air causes the cords to vibrate, generating the initial sound waves.
The vocal sac then inflates with this air, acting as a powerful resonating chamber that amplifies the sound and directs it outward. The size and shape of the inflated sac influence the call’s acoustic properties, contributing to the unique sound of each species. Crucially, the air does not fully exit the body; instead, it is cycled back and forth between the lungs and the vocal sac through the larynx. This air-recycling system allows the toad to produce continuous, long-duration trills for extended periods.
Calls Beyond Mating
While the advertisement call is the most common, toads employ other distinct calls that function as reactive communication to specific physical stimuli. The release call is a short, sharp chirp or trill given by a male when he is mistakenly grasped by another male during the breeding season. In the confusion of a chorus, a male may attempt to mate with another male; the immediate release call, often accompanied by abdominal vibrations, serves as a clear signal of gender and lack of receptivity.
Another specialized vocalization is the distress call, a high-pitched, sometimes cat-like scream emitted when a toad is attacked or seized by a predator. This loud, startling sound is thought to serve two potential purposes. It may momentarily shock the predator, giving the toad a brief window of opportunity to escape. Alternatively, the call may function to attract other nearby predators, creating a distraction or conflict that allows the toad to slip away.