How does a rat purr? - briefly
Rats generate a purr by quickly contracting the muscles around their larynx, creating a low‑frequency vibration as air passes through the vocal cords. The sound typically accompanies relaxed or social behavior.
How does a rat purr? - in detail
Rats generate low‑frequency vocalizations that resemble a purr when they are content or engaged in social grooming. The sounds originate in the larynx, where rapid oscillation of the vocal folds creates a continuous tone. Unlike the high‑pitch squeaks produced during alarm, the purring frequency ranges from 20 to 50 Hz, overlapping with the ultrasonic range used for communication.
The production mechanism involves:
- Airflow regulation: Rats contract the diaphragm and intercostal muscles to push air through the glottis at a steady rate.
- Vocal fold tension: Reduced tension allows the folds to vibrate slowly, producing the characteristic low‑frequency pulse.
- Resonance shaping: The trachea and oral cavity act as resonators, amplifying the sound and giving it a smooth, rumbling quality.
Behavioral observations show that purring occurs during:
- Resting periods: When the animal is relaxed and lying still.
- Grooming interactions: Both self‑grooming and mutual grooming with conspecifics.
- Feeding: While chewing soft foods, the rhythmic jaw movement can synchronize with the vocal output.
Experimental studies employ high‑speed video of the laryngeal region combined with acoustic analysis to measure frequency, amplitude, and duration. Electromyographic recordings reveal that the intrinsic laryngeal muscles exhibit a distinct firing pattern during these low‑frequency calls, confirming a controlled physiological process rather than an incidental noise.
The purring signal serves as a social cue, reinforcing bonds and indicating a non‑threatening state. Its acoustic signature differs from distress calls, enabling other rats to discriminate between calm and alarm contexts without visual contact.