The term “squeak” barely describes the complex world of rodent acoustic communication. Both mice and rats are highly vocal, but most of their conversations occur at frequencies silent to human ears. What a person hears as an occasional, high-pitched noise is only a small fraction of their sophisticated communication system. Rodent sound involves a spectrum of vocalizations used for everything from courtship to warning of danger.
Defining the Rodent Sound Spectrum
Rodents produce sounds using two primary laryngeal mechanisms. Lower frequency sounds, which include the rare audible “squeak,” are created by airflow-induced vibration of the vocal folds within the larynx. Higher frequency sounds are often generated by a unique whistle mechanism that involves directing air against a specialized structure in the larynx called the alar cartilage. This mechanism, similar to how a police whistle works, can generate high-pitched tones.
The upper threshold of human hearing is generally around 20 kilohertz (kHz), and this frequency serves as the division point for rodent vocalizations. Sounds below this limit are considered audible, while those above it are classified as Ultrasonic Vocalizations (USVs). The majority of social communication in both mice and rats occurs in the ultrasonic range, which can extend up to 120 kHz in mice. Because these sound waves are too high-frequency for a person to detect, their extensive vocal life often goes unnoticed.
Communication Patterns in Mice
Mice are heavily reliant on USVs for complex interactions, with most of their calls ranging between 30 and 120 kHz. Their communication repertoire is influenced by factors like age, sex, and social context. The vocalizations of mouse pups, known as isolation calls, serve a specific survival function. These short, simple USVs are emitted when a pup is separated from its mother, signaling the need for maternal retrieval behavior.
Adult mice, particularly males, use complex USVs that are often compared to birdsong. These longer, intricate “songs” are typically used in two main contexts: courtship and territorial disputes. The spectro-temporal pattern of these vocalizations can be influenced by the presence of a female, acting as non-aggressive social signaling. Audible squeaks in mice are infrequent, reserved for moments of distress, pain, or intense fighting.
Communication Patterns in Rats
Rats utilize USVs extensively, but their calls are distinctly categorized based on the emotional state they convey. Rats use two primary types of ultrasonic calls, which are strongly linked to positive or negative affective states. Long-duration USVs centered around 22 kHz are associated with aversive or negative situations, such as fear, anticipation of inescapable punishment, or pain. These lower-frequency calls can last for over 300 milliseconds and function as alarm or distress signals.
In contrast, short-duration USVs peaking around 50 kHz are indicators of a positive emotional state, often occurring during play, mating, or in anticipation of a reward. These high-frequency chirps are referred to as “rat laughter” due to their association with excitement and pleasure; their playback encourages social approach behavior. Unlike mice, rats produce audible sounds more frequently in social interactions, which may be heard during rough-and-tumble play or intense aggressive encounters.