The familiar sounds of a pond at night are typically filled with the low-frequency thrumming of a frog chorus, a symphony of croaks, chirps, and ribbits. These common vocalizations are generally understood as communication signals related to mating or territory. However, the concept of a small amphibian emitting a sound akin to a human scream often surprises people trying to understand the full range of frog acoustics. The truth is that frogs possess a complex vocal repertoire, and the most dramatic sound they produce is reserved for moments of extreme danger.
Defining the Distress Call
A frog can scream, though this sound is scientifically known as a “distress call” or a “pain shriek.” This vocalization is not part of their normal, structured communication and is almost exclusively heard when the animal is under physical duress. It is a high-pitched, piercing, and surprisingly loud shriek that can last for several seconds, often resembling the sound of a startled baby or a shrill alarm.
Unlike the rhythmic calls used to attract mates, the distress call is chaotic and urgent. It is typically triggered by a predator’s attack or when a frog is suddenly grabbed or handled. Both male and female frogs are capable of producing this loud sound.
Mechanism and Evolutionary Purpose
The production of this loud vocalization involves a rapid, forceful expulsion of air, making it distinct from the controlled, rhythmic inflation and deflation used in mating calls. Most frog sounds are created when air is passed over the vocal cords, located in the larynx, and resonated by the vocal sac under the throat. The distress call is essentially an explosive burst of sound, often accompanied by defensive body movements, such as raising the front of the body and opening the mouth wide.
In some species, such as the leaf litter frog (Haddadus binotatus), the distress call is even more complex, incorporating frequencies that extend into the ultrasonic range. These high-frequency sounds are inaudible to humans but can be heard by certain predators like bats, rodents, and small primates. This suggests the call is a defense mechanism tailored to their specific environment and threat profile.
Scientists propose two primary evolutionary functions for this vocalization. The first is the startle response, where the sudden, shrill shriek momentarily shocks or disorients the predator, offering the frog a split second to escape its grasp. The second, more complex hypothesis is that the scream acts as a beacon to attract a secondary, larger predator. The hope is that by drawing attention, the frog’s initial attacker may become the target of a different animal, leading to a distraction or struggle that allows the frog to flee.
Differentiating Frog Vocalizations
The distress call sits within a broader catalog of frog vocalizations that serve different biological needs. The most common sounds are advertisement calls, or mating calls, which are highly stereotyped and used by males to attract females of their own species. These calls provide females with information about the male’s size and suitability as a mate.
Male frogs also use territorial calls, sometimes described as a “battle cry,” to warn competing males away from a prime calling or breeding location. Another distinct sound is the release call, which a male makes when another male mistakenly attempts to grasp it during breeding season, signaling the error to the overzealous suitor.
The distress call stands apart from these structured communication sounds because it is an alarm, not a message intended for a conspecific. While mating and territorial calls are primarily limited to males, the distress shriek is a survival tool available to both sexes. Its chaotic nature differentiates it from the more measured, communicative sounds that define the typical night chorus.