Echolocation: Dolphins use echolocation for navigation and targeting prey. The f
ID: 2104951 • Letter: E
Question
Echolocation:
Dolphins use echolocation for navigation and targeting prey. The figure above shows a CT scan of a dolphin head showing the region where the bio-acoustic signal is generated. The signals emitted by many dolphins are whistles and brief broadband clicks. The right side of the above figure shows the temporal signal and its corresponding spectrum. The average duration for one of these pulses is 55 microseconds and contains approximately 4.1E-4 J of energy.
(1) Consider a bottlenose dolphin swimming in the Atlantic Ocean at a speed of 7 km/h towards a school of anchovy moving away from the dolphin at 0.3 m/s. What is the frequency observed at the anchovy school for the the peak frequency (110 kHz) of the emitted echolocation click?
(2) Assume that the bio-acoustic emission from the dolphin is contained within a cone having an angular width of 10 degrees. If the school of anchovy were 10 m from the dolphin, what is the intensity of the signal at the fish?
(3) Bats also use echolocation to navigate and track prey. However, a brown bat's bio-acoustic pulse is, on average, 22 ms long at distance and can shorten to about 0.5 ms during its final attack. These are considerably longer than the pulse width emitted by dolphins. Hypothesize why this may be the case.
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Explanation / Answer
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Most marine dolphins have a large repertoire of sounds. These include pulsedsounds of two general types: those used for echolocation (SONAR) and those emittedin emotional states. Dolphins also emit pure tone sounds called whistles and chirps.Each individual has its own unique whistle that serves to distinguish who andwhere the whistle is coming from. The loudness and the duration of the whistleare also important.
People are constantly relying on the scientists and the writers of publishedreferences and textbooks as well as topic specific books for the "acceptedvalues"of many things. It is quite ironic to find so many variations andinconsistencies among these values.
The low end ranges from 100 Hz to 8,000 Hz with three sources agreeingon a value of 1,000 Hz. The higher end of the range was more varying listingupper frequencies of 120,000 (two sources), 150,000, 164,000 and 200,000 Hz.One should seek the standard deviation of the machinery used before stating whichis wrong and which is correct. The machine deals with large quantities and thereforewhat sounds like a big difference can be considered by scientists to be minimal.
Many reasons can be listed as to why these facts differ. As the advancementsin science and machinery took place, the tools used to measure the frequenciesmay have changed in their sensitivity and accuracy. One also must take into considerationthat all the scientists might not have been using the same type of dolphin. Variationsin the location of the measurements, the size of the dolphin, the time of year,the gender, and the age of the dolphin are all variables that may have affectedthe results.
Bibliographic Entry Result(w/surrounding text) Standardized
Result Nicol, Colin. The Biology of Animals. London: Pitman, 1970: 407. "… from bottlenose dolphin pitch from 7,000 c/s–5,000 c/s. Frequencies are in sonic range from 1 kc/s–120 kc/s" 1–120 kHz Grolier Multimedia Encyclopedia. Release 6. USA: Software Toolworks, 1993. "… frequency between 1 and 120 kc/s." 1–120 kHz Stenuit, Robert. The Dolphin: Cousin to Man. New York: Sterling, 1969: 48-49. "… up to frequencies 10 times higher than a man can hear. 100 cycles/sec to 150,000 cycles/sec." 0.1–150 kHz Norris, Kenneth. Whales, Dolphins and Porpoises. Los Angeles: University of California, 1966: 503-504 "… harmonics region of frequency was from 1 kc/s to 164 kc/s" 1–164 kHz Montagu, Ashley. The Dolphin in History. Los Angeles: University of California, 1963: 43. "… frequencies from 8 kc/s to at least 200 kilocycles." 8–200 kHz Howlett, Rory. "Flipper's Secret." New Scientist. 2088 (28 June 1997), 34-39. "… frequency range between 20,000 and 120,000 cycles per second" 20–120 kHz
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