Acoustics and Echolocation

Question 1

What are some reasons why echolocation evolved?

Answer 1

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

Question 2

What are the characteristics of sound?

Answer 2

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

Question 3

Describe amplitude

Answer 3

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

Question 4

Describe sound attenuation

Answer 4

• 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?

Question 5

What two factors affect sound attenuation?

Answer 5

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

Question 6

Do higher frequencies attenuate faster or slower than low frequencies?

Answer 6

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

Question 7

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

Answer 7

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

Question 8

What is the hearing range for humans?

Answer 8

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

Question 9

What are some different types of sounds?

Answer 9

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

Question 10

Constant Frequecny

Answer 10

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

Question 11

Frequency Modulated

Answer 11

Frequency = changing with time (wavelengths vary in size)

Question 12

Broadband

Answer 12

Short duration “click”
Wide range of frequency

Question 13

Narrow band

Answer 13

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

Question 14

What is a spectrogram

Answer 14

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

Question 15

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

Answer 15

• High frequencies have a shorter wavelength
• Low frequencies have a longer wavelength

Question 16

Echolocation

Answer 16

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

Question 17

What are the only marine mammals that utilize echolocation

Answer 17

Odontocetes

Question 18

What are the three distinct processes that can characterize echolocation?

Answer 18

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

Question 19

Describe “foraging buzzes” in dolphins

Answer 19

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

Question 20

What is the source of echolocation?

Answer 20

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

Question 21

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

Answer 21

• 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

Question 22

What is believed to assist in odontocete echolocation capabilities?

Answer 22

• Cranial asymmetry
• Melon
• Nasal Sacs

Question 23

Why is the melon important for echolocation

Answer 23

• 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

Question 24

Where do incoming sounds come in for odontocetes?

Answer 24

Specialized fats in the lower jaw

Question 25

Describe how Sperm Whales echolocate

Answer 25

- 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

Question 26

What is an audiogram?

Answer 26

Displays the intensity of sounds required for an organism to hear

Question 27

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

Answer 27

The lowest portion *Higher frequencies*

Question 28

What information can we learn from the audiograms of odontocetes ?

Answer 28

Odontocetes can hear better at higher frequencies

Question 29

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

Answer 29

- Size of object - Distance to object (ex: foraging buzz) - Background noise

Question 30

How do odontocetes time echos and clicks?

Answer 30

- Outgoing clicks occur between returning echoes to reduce interference

Question 31

What are the two steps in Bottlenose Dolphin echolocation?

Answer 31

1. Target detection 2. Target discrimination

Question 32

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

Answer 32

- 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*

Question 33

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

Answer 33

- Location - Predation - Size - Prey types

Question 34

What are some examples of high frequency clickers?

Answer 34

- Harbor porpoise - Hector's dolphin

Question 35

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

Answer 35

- Live in shallow (nearshore) "cluttered" waters - Small body size *High frequency = high resolution*

Question 36

Why do high frequencies have higher resolutions?

Answer 36

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

Question 37

Why is the echolocation technique of Porpoises unique?

Answer 37

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

Question 38

What are some of the costs of echolocation?

Answer 38

- Inter-specific interception: alerting predators and prey - Intra-specific interception: alerting competitors *The energetic costs are unknown*

Question 39

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

Answer 39

- 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

Question 40

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

Answer 40

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

Question 41

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

Answer 41

- 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