Cetaceans, in general, are able to detect the presence of nearby vessels, and can use a variety of sonar and other types of sensory input to determine what is happening in the water. When animals are able to detect vehicles and signals from vessels, they are able to assess their character and purpose. While scientists have observed animals using sonar, the question of how they actually do so is not well understood. The paucity of empirical evidence leaves a significant question: could whales hear sounds in the upper ranges of the audible spectrum?
If whales can detect lower frequencies and are capable of discriminating these in their echolocation calls, then hearing of this sort is a distinct possibility. A recently published article in Frontiers in Ecology and Evolution suggests that there are several mechanisms that may be able to explain how whales and dolphins may be able to hear such high-frequency sounds. This means that there is more to our understanding of how cetaceans are able to detect and navigate in noisy environments than previously thought.
"Cetaceans may indeed be capable of hearing very high frequency sounds," says D. Hawkins, professor of biological sciences at the University of Illinois. "What they are hearing may depend on their body size and the use of sound-reflecting tissues in their heads. Regardless, if whales and dolphins are indeed capable of hearing such high frequencies, then they should be incorporated into our understanding of their ability to detect and use signals to navigate in the marine environment."
Although the eyes and ears of cetaceans are well-developed, they are used differently from those of humans. D. Hawkins explains, "The eyes and ears of cetaceans work in different ways. Their eyes do not work the same way as humans: they are not sensitive to light, and are capable of capturing images with a much wider field of view. Their ears are specialized to detect extremely low frequencies and are more difficult to calibrate than are our ears."
The emphasis on low-frequency sound detection has been built upon the work of J. Bowlin, a comparative biologist and neuroscientist at the Marine Biological Laboratory in Woods Hole, Massachusetts. Bowlin studied the low-frequency hearing capabilities of echolocating animals, using humans as his model. In 1991, he published a study showing that humans were not capable of hearing sound frequencies above approximately 100Hz. Since then, there have been limited studies, but no published research, on the high-frequency hearing capabilities of cetaceans.
The higher the frequency of a sound, the shorter its wavelength. In order to make sense of what is being said, it is important to understand what frequencies are heard by humans. In the case of humans, the most prevalent range of audible sound is 0 to 16kHz. While most adults can hear frequencies up to approximately 16kHz, it is difficult to hear anything above that.