Communicating Over Long Distances

a large cassowary bird with black body blue head and distinctive horn on head walks amongst greenery

Biological Strategy

Double-wattled cassowary

AskNature Team

Image: Mosista Pambudi / Wikimedia Commons / CC BY SA - Creative Commons Attribution + ShareAlike

Send Sound Signals

Many living systems send auditory signals to communicate with others, including to attract, announce, or warn. These sounds must be audible to the intended recipient in a variety of conditions, such as in wind, water, and solids. As a result, each living system has specific sounds best adapted to its environment. For example, some birds live in loud habitats, like those alongside noisy streams or in windy areas. These birds use sound frequencies that can be heard by other birds over competing environmental noises.

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Sense Sound and Other Vibrations From the Environment

For living systems, sensing sound and other vibrations is important for communicating and detecting conditions within their environment. Living systems must locate a signal’s source so that they can move toward it (such as when it is food or a potential mate) or away from it (such as when it is a predator). To prompt an appropriate response, living systems must sense these signals, recognize their amplitude or volume (which is sometimes very low), and determine their direction. Living systems must be attuned to signals relevant to them and able to distinguish these from irrelevant sounds to avoid expending unnecessary energy. For example, owls’ ears are asymmetrically placed. This enables them to detect sounds more accurately, which helps them locate small prey at night and avoid wasting energy chasing down irrelevant sounds.

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Birds

Class Aves (“bird”): Eagles, hawks, sparrows, parrots

Birds are evolutionary engineering marvels. They are descended from dinosaurs, but are far from our idea of heavy, scaly reptiles. Of the specific adaptions that set them apart, most notable is flight—although some mammals can fly, birds take the prize for abundance in the skies. Many birds have hollow, lightweight skeletons and specially-designed wings to help them stay aloft. They also have feathers made of keratin that help them stay warm, attract mates, and improve navigation and aerodynamics in flight. In contrast to their dinosaur ancestors, they lack true teeth and have replaced them with specialized beaks and bills.

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Cassowaries communicate over long distances in dense rainforest using low frequency booming sounds.

“Although some birds can detect wavelengths in the infrasound range, there has been little evidence that birds produce very low frequencies. We made nine recordings of a captive Dwarf Cassowary (Casuarius benneti) and one recording of a wild Southern Cassowary (C. casuarius) near Crater Mountain, Papua New Guinea. Both species produced sounds near the floor of the human hearing range in their pulsed booming notes: down to 32 Hz for C. casuarius and 23 Hz in C. benneti. Recordings of C. benneti indicate four levels of harmonics with the 23 Hz fundamental frequency. Such low frequencies are probably ideal for communication among widely dispersed, solitary cassowaries in dense rainforest. The discovery of very low-frequency communication by cassowaries creates new possibilities for studying those extremely secretive birds and for learning more about the evolution of avian vocalizations.” (Mack and Jones 2003:1062)