Animal Behavior - Biology 4200/5430 |
Bowling Green State University, Fall 2009 |
Acoustical signals: Sound is a compression wave which travels from the source as a series of high pressure peaks separated by troughs of low pressure. The stimulus energy are mechanical oscillations of high and low pressure which impart energy to the sound detecting sensory structures. Sound waves carry information via amplitude modulation (changes in loudness, AM) and frequency modulation (changes in pitch, FM). Amplitude represents the pressure difference (in decibels - dB) between the peak and trough. The frequency describes how many times the wave cycles per second. Frequency (f) = cycles/s [in Hz]; Period (t) = duration [in s]; t = 1/f; Speed of propagation (c) depends on medium: cair 344m/s, cwater 1500m/s; Wavelength (l) = t * c; Object needs to be >1/6th of wavelength to appreciably diminish amplitude
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Plot of varying sound pressure at a specific location over time. If you replace the x axis label "Time" with "Distance from a specific location" this graph represents a plot of varying sound pressure levels as a function of distance from source © lobsterman |
Sound waves are detected by specialised mechanoreceptors, based either upon hair cells (common in vertebrates) or stretch receptors (e.g., chordotonal organs of insects). These sensory cells are usually connected to a tympanum, or eardrum, which is free to vibrate in response to changes in air pressure. The eardrum is often backed by an air-filled space so that the difference in pressure between the two sides of the membrane is sufficient to cause the membrane to deflect inwards or outwards. These deflections are then transmitted to receptor cells, which responds with a receptor potential.
Discuss: Long distance communication of elephants, frogs and insects; Bat echolocation; Sound localization of humans and insects; Underwater orientation of dolphins and whales
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