The question of the quietest bird presents a complex challenge because avian quietness is not a single characteristic. Birds may achieve near-silence in their flight or in their vocal communication, and the species that excels in one area often differs from the one that excels in the other. Determining a single “quietest bird” requires evaluating two distinct biological mechanisms for sound production: the loudness of its song or the sound produced by its movement through the air. This distinction provides the framework for identifying the true masters of avian silence.
Understanding Avian Silence: Vocalization vs. Aerodynamics
Avian sound production can be separated into two main categories: vocalization and mechanical noise. Vocalizations are generated using the syrinx, the bird’s unique vocal organ located at the base of the trachea, where it branches into the lungs. Sound is produced when air flowing through the syrinx causes membranes and labia to vibrate, and the amplitude of these vibrations determines the loudness of the call or song.
Mechanical noise, conversely, is the sound created by the physical movement of the bird, primarily its wings during flight. This noise is largely a product of air turbulence generated as the wings flap and push through the atmosphere. While all birds generate some level of turbulence, certain species have evolved specialized structures to minimize this aerodynamic sound.
Masters of Silent Flight
The most famous examples of quiet flight are the owls, which have evolved specialized feather structures to enable stealthy hunting. Their wings often feature three distinct adaptations that work together to disrupt and dampen air turbulence.
The leading edge of the primary flight feathers has a comb-like serrated structure that acts like a silencer, breaking up large, noisy eddies of air into smaller, quieter currents. The flight feathers also have a soft, velvety texture on their surface, which reduces frictional sound as the feathers rub against each other during the flapping cycle. Finally, the trailing edge of the wing feathers possesses a soft fringe, which further reduces the sound generated by the air flowing off the wing.
These adaptations allow large species, like the Barn Owl, to fly with noise levels measured as low as approximately 28 decibels, making them virtually inaudible to human ears at typical hunting distances. This near-silent movement is important for owls hunting prey with acute hearing, allowing the owl to avoid self-masking the faint sounds of its prey moving on the ground.
Birds That Rarely Vocalize
Low Amplitude Vocalizations
A different form of quietness is found in birds that produce sounds of extremely low amplitude. Many small passerines, such as finches and canaries, are considered quiet because their vocalizations are soft chirps and peeps. Although they may vocalize frequently, their tiny size naturally limits the volume of their songs, rarely exceeding 65 to 70 decibels, which is comparable to normal human conversation.
Infrasound Communication
Other species utilize low-frequency vocalizations that are difficult for humans to perceive, especially from a distance. The Western Capercaillie, a large grouse, produces display vocalizations that include fundamental frequencies as low as 25.6 to 31.6 Hertz. Similarly, certain cassowaries produce booming calls with fundamental frequencies as low as 23 Hertz, which are essentially infrasound. These low-frequency sounds fall near the threshold of human hearing and may serve as long-distance communication signals, but their extremely low frequency makes them practically silent to a person standing nearby.
Identifying the Quietest Candidates
The title of “quietest bird” must be shared by multiple candidates, depending on the measured criteria. If quietness is based on the lowest mechanical noise during locomotion, owls are the undisputed champions due to their specialized feather structures. Their ability to approach prey without detection demonstrates the most effective suppression of aerodynamic sound.
If quietness is defined by the lowest amplitude of vocal output, the winners are often smaller birds like finches or doves, whose calls are soft and unobtrusive. The most profoundly “silent” birds to the human ear might be those that communicate using infrasound, such as the cassowaries or capercaillies. These species produce sounds that are physically massive but are mostly registered as a low, barely perceptible rumble rather than a loud call.