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MAR 370 > Acoustics and Echolocation > Flashcards

Acoustics and Echolocation Flashcards

1
Q

What are some reasons why echolocation evolved?

A
  • Sound propagation (sound travels faster and farther in water than in air)
  • Low visibility (light is scarce in deep waters)
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2
Q

What are the characteristics of sound?

A
  • Frequency (cycles per second (Hz))
  • Wavelength (λ)
    λ = c/f
  • C = speed of sound
  • F = frequency
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3
Q

Describe amplitude

A
  • Loudness
  • The amplitude of a sound wave is characterized by its sound pressure level (SPL)
    Sound pressure level is measured in decibels
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4
Q

Describe sound attenuation

A
  • Decrease in sound intensity over space
  • P / 4πr² = I
  • P = Power
  • 4πr² = Area of a sphere
  • I = intensity
  • As you move farther from a source, energy has to travel farther to reach the object. As the object gets bigger, the energy must spread over a larger area.
    Why is sound attenuation important for marine mammals?
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5
Q

What two factors affect sound attenuation?

A
  1. Absorption: viscosity / thermal conductivity
  2. Scattering: sound strikes foreign bodies
    High frequencies = more suseptible to absorption
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6
Q

Do higher frequencies attenuate faster or slower than low frequencies?

A

Faster
(Higher frequencies do not travel as far as low frequencies)

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7
Q

Describe the relationship between the sounds that marine mammals produce and the range in which they can hear

A

Marine mammals have a range of sounds that they can produce ad this matches the range of sounds that they can hear

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8
Q

What is the hearing range for humans?

A

20 to 20,000 Hz (20kHz)
- Ultrasonic > 20kHz
- Infrasonic < 20 Hz

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9
Q

What are some different types of sounds?

A
  1. Constant frequency (CF)
  2. Frequency modulated (FM)
  3. Broadband
  4. Narrow band
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10
Q

Constant Frequecny

A
  • Pure tone
  • Stable oscillation period (wavelengths all = the same size)
  • Amplitude or loudness (hight of waves) can vary
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11
Q

Frequency Modulated

A

Frequency = changing with time (wavelengths vary in size)

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12
Q

Broadband

A

Short duration “click”
Wide range of frequency

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13
Q

Narrow band

A
  • Tonal “whistle”
  • High frequency
  • Long duration
    Small range of frequency
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14
Q

What is a spectrogram

A
  • Plots frequency vs. time
  • Reflects the tone that an animal is producing over time
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15
Q

Do high frequencies have a longer or shorter wavelength than low frequencies?

A
  • High frequencies have a shorter wavelength
  • Low frequencies have a longer wavelength
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16
Q

Echolocation

A

The ability to orient by transmitting sound and receiving echoes from objects in the environment
Similar to sonar sound navigation and ranging

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17
Q

What are the only marine mammals that utilize echolocation

A

Odontocetes

18
Q

What are the three distinct processes that can characterize echolocation?

A
  1. Sound production: outgoing signal
  2. Sound reception: sound bounces off a target and comes back
  3. Signal processing: interpretation of sound information
19
Q

Describe “foraging buzzes” in dolphins

A

Series of clicks that get closer together as the dolphin gets closer to its prey

20
Q

What is the source of echolocation?

A
  • Current hypothesis: Monkey Lips / Dorsal Bursae Complex
  • Previous Hypothesis: Larynx
21
Q

Describe the Monkey Lips / Dorsal Bursal Complex (phonic lips) and how they produce echolocation clicks

A
  • Valves made up of ridges located in the walls of the nasal passage
  • Air is pushed through the monkey lips at pressure that vibrates the air, lips, and surrounding tissue
  • Sound is transferred into the melon for eventual transmission into the water column
22
Q

What is believed to assist in odontocete echolocation capabilities?

A
  • Cranial asymmetry
  • Melon
  • Nasal Sacs
23
Q

Why is the melon important for echolocation

A
  • Comprised of metabolically inactive fatty acids
  • Core of the melon is composed of less dense fat than outer layer (slower rate of sound transmission)
  • As sound passes through the core it is refracted (narrowing the sound beam) and reflected (focusing the sound beam forward)
    The melon is different in different families of odontocetes
24
Q

Where do incoming sounds come in for odontocetes?

A

Specialized fats in the lower jaw

25
Q

Describe how Sperm Whales echolocate

A
  • Spermaceti organ located in the enormous cranium secretes a waxy oily liquid
  • Sounds are produced by the phonic lips at the front of the head
  • The spermaceti organ sends the sound backwards first
  • Sound travels through he spermaceti organ until it is reflected by air sacs at the back of the organ
  • The sound then moves forward where it is refracted by the cranium
  • This allows the whales to build a 3D image of their surroundings
26
Q

What is an audiogram?

A

Displays the intensity of sounds required for an organism to hear

27
Q

What portion of an audiogram represents the best hearing for an organism?

A

The lowest portion
Higher frequencies

28
Q

What information can we learn from the audiograms of odontocetes ?

A

Odontocetes can hear better at higher frequencies

29
Q

How do the number, source level, and time intervals between clicks vary in odontocetes?

A
  • Size of object
  • Distance to object (ex: foraging buzz)
  • Background noise
30
Q

How do odontocetes time echos and clicks?

A
  • Outgoing clicks occur between returning echoes to reduce interference
31
Q

What are the two steps in Bottlenose Dolphin echolocation?

A
  1. Target detection
  2. Target discrimination
32
Q

How big does a target have to be in order for it to be detected by a Bottlenose Dolphin?

A
  • Diameter of target must be > 1 wavelength (0.01m)
    This is how big the object must be in order for the dolphin to detect it
33
Q

What are some factors that have driven different odontocete species to have the echolocation clicks that they use today?

A
  • Location
  • Predation
  • Size
  • Prey types
34
Q

What are some examples of high frequency clickers?

A
  • Harbor porpoise
  • Hector’s dolphin
35
Q

Why do the Harbor Porpoise and Hector’s Dolphin have high frequency clicks?

A
  • Live in shallow (nearshore) “cluttered” waters
  • Small body size
    High frequency = high resolution
36
Q

Why do high frequencies have higher resolutions?

A

They have shorter wavelengths and narrower beam widths resulting in better axial and lateral resolution
Why don’t all odontocetes produce high frequency clicks?

37
Q

Why is the echolocation technique of Porpoises unique?

A

Porpoises utilize a frequency range that no other organisms uses making them undetectable to predators and prey

38
Q

What are some of the costs of echolocation?

A
  • Inter-specific interception: alerting predators and prey
  • Intra-specific interception: alerting competitors
    The energetic costs are unknown
39
Q

What is the passive listening hypothesis (Bottlenose Dolphins) and describe the experimental procedure done to test this hypothesis?

A
  • Bottlenose dolphins prey on soniferous fish
  • It is believed that dolphins passively listen rather than actively echolocate in order to detect their prey
    …………………………………………………………………………………..
    Experimental Procedure:
  • Control stimulus: Snapping shrimp (dolphins do not eat this)
  • Experimental stimulus: Croaker (soniferous prey item for bottlenose dolphins)
  • Dolphins stopped echolocating / started listening when they heard the croaker sounds
40
Q

What are the differences in echolocation between transient and resident killer whales?

A
  • Transient killer whales: feed on marine mammals - infrequent echolocation (irregular clicks)
  • Resident killer whales: feed on salmon - frequent echolocation
41
Q

What evidence suggests that Harbor Porpoises high frequency clicking is an adaptation used to avoid predation?

A
  • Harbor Porpoises click above the hearing range of killer whales
  • We would expect to see Harbor Porpoise whistle frequency above killer whales as well however, they DO NOT WHISTLE

MAR 370 (10 decks)

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