Sound exists across a wide spectrum of frequencies, much of which lies beyond human perception. Infrasound refers to sound waves with frequencies below 20 Hertz (Hz), the typical lower limit of human hearing. These low-frequency sounds possess unique characteristics that enable them to travel long distances and penetrate obstacles, making them particularly useful for communication and environmental sensing in the animal kingdom.
The Unique Properties of Infrasound
Infrasound’s distinct physical properties make it an effective medium for long-range transmission. Its long wavelengths mean it is less susceptible to scattering and absorption by the environment. This allows infrasound to travel with minimal energy loss over vast distances. Infrasound can also penetrate dense materials like solid ground, water, or thick forests. Atmospheric conditions, including refractive ducting between the Earth’s surface and the stratosphere, can also influence infrasound propagation, extending its reach.
Animals That Communicate with Infrasound
Many large animals utilize infrasound for complex communication, leveraging its ability to travel far and bypass obstacles. Elephants employ extensive infrasonic vocalizations for long-distance communication across their vast habitats. These powerful, deep rumbles, ranging from 15 to 35 Hz and reaching up to 117 decibels, help coordinate group movements and signal the presence of estrous females to distant males. Elephants can also produce infrasound waves that travel through the ground, which other herds sense through their feet, allowing communication over ranges up to 32 kilometers.
Marine mammals like fin whales and blue whales also rely on infrasound to navigate and find mates across expansive ocean basins. Blue whale calls, ranging from 10 Hz to 31 kHz, can travel for hundreds or thousands of kilometers underwater. The density of water facilitates the long-distance transmission of these low-frequency sounds.
Rhinoceroses use low-frequency rumbles for communication, particularly in dense forest habitats. Sumatran rhinoceroses produce sounds as low as 3 Hz, including “whistle-blows” at 17 Hz. These calls are thought to play a role in mating, with females potentially using infrasound to indicate their reproductive receptivity.
Okapis, secretive forest dwellers, also use infrasound for discreet communication. Okapi mothers are known to use calls around 14 Hz to communicate with their calves. This allows them to “check in” without alerting potential predators in the dense forest environment.
While not definitively proven to use infrasound for communication, giraffes have been observed to produce low-frequency “humming” noises at night. Although initial theories suggested infrasonic communication, recent studies indicate these hums are typically within the human audible range, averaging around 92 Hz. These nocturnal vocalizations may serve as contact calls to maintain social cohesion when visual cues are limited.
Animals That Use Infrasound for Environmental Sensing
Some animals detect naturally occurring infrasound to sense their environment and predict events. Homing pigeons are sensitive to infrasound, aiding their navigation. They can detect sounds as low as 0.5 Hz, with a sensitivity at least 50 decibels greater than humans below 10 Hz. This allows them to potentially use infrasonic signals from distant geographical features or even large-scale weather phenomena as a “map” for orientation.
Other bird species utilize infrasound to detect approaching weather systems. Golden-winged warblers, for example, were observed fleeing their breeding grounds hours before a severe storm system. Scientists believe these birds detected the infrasound generated by the distant tornadoes, which can travel for thousands of kilometers. This sensitivity may provide an early warning system, allowing birds to evade destructive weather events.
Tigers use the infrasonic components of their roars to disorient and potentially immobilize prey. Their powerful roars contain infrasound frequencies of 18 Hz or lower. These low-frequency vibrations can cause a momentary sensation of shock or disorientation in an animal, rather than true paralysis, making it easier for the tiger to capture its prey.