The voices of nature: Who makes sounds and why?
Virtually all animal species make sounds and they do so in a variety of ways, for a variety of reasons. A single species can produce different sounds depending on the context, e.g., trying to attract a mate, communicating with an infant or juvenile, or warning others of a predator.
Fortunately, these calls are usually species-specific, which means that the frequency range, dominant frequency, duration, and pattern of sound production are unique to each species. Species-specific calls maximize communication within a species and avoid confusion between species. In this section, we describe how and why sounds are produced by insects, fish, amphibians, birds, and mammals.
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Insects
Insects emit sounds at a wide range of frequencies, including calling songs, advertisement calls, aggressive calls, and rivalry songs. The three major contexts of sound emission in insects are (a) female attraction, (b) male-male competition, and (c) female-male communication.
The mechanisms of sound production in insects include tremulation, percussion, stridulation, buckling, and expulsion of air. Among the loudest insects are the cicadas and water boatmen. Some cicadas can emit sounds up to 150 dB, which is louder than a jet engine! Insects do not have to be large to produce loud sounds. Male water boatmen are small aquatic insects only 2 mm long and can produce a courtship call up to 99 dB by stridulating a ridge of its penis across corrugations on its abdomen. Insects can also emit high-frequency sounds not audible to humans (> 20 kHz).
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Fish
Fish emit a variety of ‘soft’ and low frequency (~1 kHz) sounds including grunts, moans, calls, and clicks. These sounds are associated with courtship and spawning, territoriality, and stress behaviors. Most sounds are produced by males to attract females. In many species, the males aggregate in spawning sites at night and call for hours.
The most common mechanisms of sound production in fish are stridulation and drumming. Fish stridulate by rubbing together their jaw or pharyngeal teeth, specialized spines (in catfish), or bony edges of the skull (in seahorses). Many fish have specialized sonic muscles that expand and contract the swim bladder to generating drumming sounds. These are the fastest contracting muscles known for vertebrates! Here are examples of the drumming of croakers, and the moans of toadfish and midshipman.
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Birds
Birds are prodigious singers that emit simple and complex vocalizations. Sound production involves the lungs, air sacs, and the syrinx (an organ located at the junction of the trachea). Many species learn the calls from conspecifics, and a few species, like mockingbirds and lyrebirds, can also mimic the calls of other species. Many species of birds also emit distress and warning calls when a predator is nearby. Song/call frequency ranges from infrasonic (30 Hz) in Cassowaries to ~10 kHz in passerine species. Hummingbirds can produce high-frequency (~13 hKz) chirps when calling mates.
Northern Mockingbird Sounds, All About Birds, Cornell Lab of Ornithology
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Mammals
Mammals use sound for close and long-range communication. They emit sound in a variety of contexts including species and individual identification, advertisement of reproductive or social status, defense of territories, detection of predators, localization of prey, and social interactions.
Most sounds are generated with the larynx and vocal cords and range from 10 Hz to above 50 kHz. Exceptions are some bat species and the toothed whales, including dolphins. Bats use echolocation for navigating and hunting prey. They also produce sounds for social interactions. Because the sounds are in the ultrasonic range, recordings must be slowed down for humans to hear them. Toothed whales can produce sounds above 100 kHz using specialized air sacs near their blowhole. Mammals can also produce non-vocal sounds for communication. For example, tenrecs rub quills on their backs generating a high-frequency sound, and some species of deers and bovids produce clicking or cracking sounds with their joints and knees as they walk.
Photo credit:
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Amphibians
Amphibians are the singers of the night, although some species are diurnal and call during the daytime. Their calls are not as complex as those of birds, but they are persistent. Amphibians can call for hours with hardly a break.
Sound emission in amphibians involves the lungs, vocal cords, and vocal sacs (when present). In most species, males are the primary sound emitters, relaying information to females and competitors about their location, species identity, and readiness to mate. Their calls are often a chirp or a series of chirps with frequencies between 2 to 6 kHz. However, some species can emit calls with the ultrasonic range (above 20 kHz), for example, the concave-eared torrent frog (Odorrana tormota).
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