Toads, amphibians known for their distinctive sounds, use these vocalizations as an important aspect of their communication. These sounds, often described as croaks or trills, are not random noises but serve various specific purposes. Understanding these vocalizations provides insight into their lives.
The Chorus of Courtship
Male toads exclusively use vocalizations to attract mates during breeding season, which occurs in spring or early summer as temperatures rise. These advertisement calls signal their presence, species, and their fitness to receptive females. Each toad species possesses a unique call, allowing females to identify suitable partners even within a chorus of many calling males.
Females evaluate these calls to locate and select mates for reproduction. The intensity, frequency, and duration of a male’s call can indicate his size and overall health, factors important for successful breeding. Male toads often gather near water bodies, such as ponds or streams, and their collective calling creates a chorus that can be heard from a distance, drawing in females. This acoustic display is an energy expenditure for males, highlighting its importance in their reproductive strategy.
Defending Territory and Signaling Distress
Beyond attracting mates, toads also use vocalizations for other important interactions. Males may emit calls to warn off rival males, establishing or defending their breeding territory from competitors. These territorial calls differ in pattern or intensity from courtship calls, acting as a direct signal to deter other males. Such aggressive vocalizations are part of male-male competition, where higher frequency calls indicate a smaller, less threatening rival.
Toads, both male and female, can also produce a sharp distress call when grasped by a predator or another toad. This piercing sound serves as a defensive mechanism, startling the attacker or signaling to other animals that prey on the threat. Additionally, a distinct “release call” is emitted by a male toad or an unreceptive female when mounted by another male, signaling that they are not a suitable partner for mating. This ensures that mating attempts are directed at appropriate individuals, preventing wasted energy and harm.
The Mechanics of a Croak
The production of a toad’s croak involves a specialized anatomical process. Toads produce sound by forcing air from their lungs over their vocal cords, which are located in the larynx. These vocal cords vibrate as air passes over them, generating the initial sound. A unique feature in male toads is the vocal sac, an inflatable pouch located on their throat.
This vocal sac acts as a resonator, amplifying the sound produced by the vocal cords, allowing the call to travel over long distances. When a toad croaks, it inflates this sac, which then expands like a balloon. Air is cycled back and forth between the lungs and the vocal sac without being expelled, creating a continuous sound. The physical act of croaking requires muscular effort, as the entire toad’s body can vibrate during a call.