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Mode
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Directionality
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Difficulties
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Speed
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Distance
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Infrasound Less than 20 HZ |
Infrasound may be perceived as substrate vibrations or as sympathetic vibrations of the receiver's body. Localization is difficult in these cases. | Requires a large amount of energy to produce. Also, structures for producing very low sounds are usually large (think of a bass fiddle), so infrasound is more frequently used by large animals. | 300 meters/sec in air, much faster in water (1500 meters/sec) or soil (more than 2000 meters/sec) | Because they carry considerable energy, low pitched sounds travel effectively for long distances. |
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Sound 20-20000 HZ examples: bird songs |
Locating the source of a sound depends on triangulation. Paired ears allow such triangulation, but locating sound may still be difficult, particularly if echoes are present. | Many factors may interfere with communication by sound. These include materials which absorb (muffle) or reflect sound. Sound communication is also particularly subject to interference by other sources of sound (noise). | 300 meters/sec in air, much faster in water (1500 meters/sec) or soil (more than 2000 meters/sec) | Sound energy is absorbed relatively rapidly as it travels through air or water, limiting transmission distances. Territorial calls are often low-pitched, allowing them to be heard from great distance. |
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Ultrasound More than 20000 HZ examples: bat vocalizations, rodent pups
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Bat echolocation is a good example of using sound for directional information. |
Very high pitched sounds require less energy to produce. Consquently they do not carry well through absorptive materials. |
300 meters/sec in air, much faster in water (1500 meters/sec) or soil (more than 2000 meters/sec). | Given their lower energy, high pitched sounds do not provide effective long-distance communication. |
| Highly directional. Works well for point to point communication, or as a signal to help other animals orient. | Works best with clear line of sight. Blocked by environmental obstacles, Attenuated by water over short distances. Most visual signals require ambient light to be effective. Fireflies and other animals that produce their own light are exceptions. | Very rapid. Speed of light is, for all practical purposes, instantaneous in air and water. *** km/sec. | Low energy signal may be perceived over long distance. Absorbance of light in air is less of a factor than with sound, but in water absorbance of light is a significant limitation. | |
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Chemical (odor) examples: insect sex pheromones |
Moves by diffusion in all directions, but may become directional if wind or water current is available. Disrupted by unsteady or shifting winds or water. | Any barrier to the motion of air or water also prevents carraige of odors. | Slow, depends on ambient wind speed. Up to *** km/sec. | Requires production of large quantities of odor for long distance communication, as odor molecules are rapidly diluted by diffusion in the medium. Highly acute receptors help to overcome this limitation. |
| Highly directional. | Limited by need for contact. | Can be rapid; limited by reaction time of the animal. | Necesarily a short-distance mode of communication, as the animals must be close enough to touch. | |
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Electrical examples: weakly electrical fish production of electrical signals
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Assymetries in the electrical field around its source give directional information. | Virtually no penetrance in air. In water, penetrance depends on resistance of water; distilled water is poor conductor. Water with higher ionic concentrations conducts well. | Very rapid. Speed of electricity is, for all practical purposes, instantaneous in air and water.*** km/sec. | Weakly electrical fish, which use electrical signals in communication, produce low voltage signals which are not perceptible over great distances. |