Rats are highly social mammals that rely on vocalizations to communicate within their colonies. Their repertoire includes a wide spectrum of sounds, many of which fall outside the range of human hearing. Understanding these signals helps clarify their social interactions, emotional states, and presence in a given location. This exploration details the noises rats produce, distinguishing between audible sounds and the hidden acoustic world they inhabit.
Audible Sounds of Rat Presence
The sounds a person is most likely to hear are generated by the rats’ movement and daily activities, not their actual vocalizations. A common indicator of their presence is a faint scratching or scuttling sound heard inside walls, ceilings, or attics. These noises typically happen at night, as rats are primarily nocturnal, and result from them navigating structural voids or gathering nesting materials.
Another frequently heard noise is gnawing, a necessary behavior because rats’ incisor teeth grow continuously. They chew on various materials, including wood, plastic, and electrical wiring, to wear down their teeth, producing a distinct, rasping sound. High-pitched squeaking or hissing is generally only audible to humans when the animal is in extreme distress, pain, or engaged in a physical confrontation.
Rats also produce a distinctive chattering or grinding of their teeth, known as bruxing. This sound can signal contentment, similar to a cat’s purr, often accompanied by relaxed body language. However, bruxing can also be a reaction to stress or discomfort, requiring observation of the rat’s posture to determine the emotional context. On occasion, rats may stamp their hind feet rapidly against a surface, known as foot drumming, which serves as a warning signal to alert other colony members to a threat.
Ultrasonic Vocalizations: The Unheard Language
The majority of rat communication occurs in the ultrasonic range, at frequencies above the 20 kilohertz (kHz) limit of human hearing. These Ultrasonic Vocalizations (UVs) are crucial for social bonding and conveying emotional states within the colony. Scientists categorize these calls into two main frequency bands, each corresponding to a different affective state.
Vocalizations centered around 50 kHz are associated with positive emotions, such as anticipation, play, mating, and social rewards. These higher-frequency calls are typically short and characterized by complex, high-frequency modulation. They are sometimes referred to as ‘rat laughter’ due to their association with pleasurable experiences. Playback of these 50-kHz calls often elicits an approach response from other rats, indicating their role as an appetitive social cue.
In contrast, vocalizations centered around 22 kHz signal negative affective states like distress, fear, alarm, or the presence of a predator. These lower-frequency sounds are longer, sometimes lasting up to 3.5 seconds, and are less frequency-modulated than the positive calls. The 22-kHz calls can trigger an avoidance or freezing response in nearby conspecifics, functioning as alarm cries within the social group.
Decoding Rat Behavior Through Noise
Interpreting the context of the sounds a rat makes provides insight into the status of a population. Since rats are generally nocturnal, hearing pronounced scratching or movement during the daytime might suggest a large population density or a desperate search for food or water. Continuous or very loud noises, especially audible squeaks and hisses, often point to an active confrontation, such as a fight over territory or resources.
The complexity of the ultrasonic vocalization system underscores the sophisticated social structure of rat colonies. The ability to communicate distinct emotional states through UVs enables coordinated social behaviors, such as seeking out a conspecific in a positive state or collectively responding to danger. This social organization contributes to the difficulty of managing established rat populations, as their communication facilitates group cohesion and survival.
Observing bruxing alongside a rat’s body language is the clearest way to determine its intent, as this sound can be ambivalent. If the rat is relaxed, with loose posture and a gentle eye wobble, the bruxing indicates contentment. If the teeth grinding is accompanied by a tense body, pinned ears, or avoidance behavior, it suggests the animal is experiencing anxiety or agitation. A combination of audible activity and an understanding of their inaudible language is necessary to comprehend the messages rats are conveying.