The blue whale, the largest animal known to have ever lived, is widely reputed as the loudest creature on Earth, a perception stemming from the immense power and far-reaching nature of their vocalizations. This article explores the validity of this claim by examining blue whale sounds, the complexities of marine sound measurement, and comparing their acoustic output to other animals.
The Blue Whale’s Acoustic Prowess
Blue whales produce low-frequency sounds, including moans, pulses, grunts, and groans. These vocalizations are typically infrasound, below human hearing, with fundamental frequencies from 8 to 25 Hz, though some calls reach 188 Hz. An Antarctic blue whale’s vocalization source level has been estimated at up to 189 underwater decibels (dB).
These powerful, low-frequency sounds serve purposes such as communication, navigation, and foraging. Male blue whales produce complex songs, often in repeated sequences, likely for reproduction. Short, down-swept “D calls” are used by both sexes, possibly as contact calls. The low frequency of these calls allows them to travel incredible distances through the ocean, enabling communication across hundreds or even thousands of miles.
Defining and Measuring Sound in Marine Environments
Measuring sound underwater differs from measuring sound in air. The decibel (dB) scale is referenced to 1 micropascal (µPa) in marine environments (“dB re 1 µPa”). This reference pressure is significantly lower than the 20 µPa used for sound in air, meaning underwater decibel levels are not directly comparable. Sound pressure level (SPL) is a common measure, often using root-mean-square (rms) pressure.
Sound propagation in water is influenced by temperature, salinity, and depth. Sound travels faster and further in water than in air because water is denser and its molecules are more closely packed. Hydrophones, specialized underwater microphones, detect and record acoustic signals. These devices convert pressure fluctuations into electrical signals, allowing researchers to analyze marine mammal vocalizations and other underwater sounds.
Contenders for the Loudest Title
While blue whales are loud, other animals produce sounds that challenge their claim to the loudest title. Sperm whales generate clicks up to 230 decibels, primarily for echolocation to navigate and hunt prey in the deep ocean. These directional clicks serve a different purpose than blue whale calls.
The snapping shrimp can produce a cavitation bubble that, upon implosion, creates a shockwave exceeding 200 decibels. This instantaneous snap stuns prey and deters rivals. On land, howler monkeys produce calls up to 140 decibels, using enlarged hyoid bones to amplify their vocalizations, which can travel for miles through dense forests. African cicadas are among the loudest insects, reaching 107 decibels from a distance of 50 centimeters.
The Blue Whale’s Unique Acoustic Impact
Despite higher peak decibel levels from other animals, blue whales are often considered the “loudest” in a specific context due to their sounds’ unique characteristics. Their vocalizations are sustained, low-frequency sounds that travel across entire ocean basins. While a sperm whale’s click is louder at its source, it is a brief, directional burst. Blue whale calls propagate over immense distances with minimal energy loss, particularly within the ocean’s deep sound channels.
This ability to produce powerful, continuous low-frequency sounds allows blue whales to communicate across vast ocean expanses, sometimes up to 1,600 kilometers (1,000 miles) away. Their acoustic output is impactful, permeating large volumes of the marine environment. The vibrations from their calls are strong enough to be detected by accelerometers on tags attached to the whales, indicating the physical force of these infrasonic emissions.