7. An Introduction to cetatceans & Sound

Question 1

Orders of cetaceans

Answer 1

Cetacea - odontocetes (68) & Mysticetes (11)
Sirenia - Manatees (3) & Dugong (1)
Carnivoria - divide their time between air and water (pinnipeds, otters & polar bears)

Question 2

How is sound used by cetaceans

Answer 2

Live in a world of sound not sight
Sight isn’t their principal sensory mechanism due to:
- Light penetration
- Biological species and particulates
- Sea state

Question 3

WHy sound?

Answer 3

In water light & electromagnetic waves propogat efaster and have greater resolving power than sound.
Limited range (10’s of m’s)
Sound propogates over a range of biologically sig distances depending on it’s frequency (from m’s - 1000’s of km’s)
At higher speeds in water ( 1500 ms^than air (340ms^-1)
Higher frequencies give increased resolution but over a limited distance.

Question 4

Vibrations in water are along the propogation of…

Answer 4

Vibrations in water and other fluids are along the direction of propogation ( energy is a propogated parallel to the source) and referred to as longitudinal waves.

Question 4

What is sound

Answer 4

Acoustic energy in water consists of molecular vibrations that travel at speed of sound.
Scattering and reflection processes can occur and lead to transverse waves
These sound or longitudinal waves are then detected by a receiver as changes in pressure

Question 5

What are acoustic waves characterized by

Answer 5

by their amplitude, frequency, wavelength, phase, speed and intensity

Question 6

Amplitude is

Answer 6

Is proportional to the maximum distance a vibrating Distances to how high the wavelength goes. the peak pressure reached in one cycle.

Question 7

Wavelength is

Answer 7

The distance between two sucessive supressions or the distance the wave travels in one cycle of vibration

Question 8

Frequency

Answer 8

When trying to identify sound in hertz or kilohertz.
Is the rate of oscillation or vibration of the wave particles.
ie, the rate that pressure cycles from high, to low, to high.
Number of oscillations per second

Question 9

Phase is..

Answer 9

The phase of an acoustic wave can be best described as its alignment with other propagating waves with respect to time.

Question 10

Speed of sound is…

Answer 10

‘c’

Question 11

Speed of sound in water is affected by…

Answer 11

As temp decreases with depth, speed decreases.
Change in salinity results in a 1.3s^-1 change in speed of sound.
As pressure increases with depth c increases

Question 12

Sound intensity looks at

Answer 12

Decibel scale. - unit: dB
Sound pressure scale SPL and sound intensity level SIL

Question 13

Terms describing sound reception

Answer 13

Can be recieved with hydrophones, microphones.
Are transduers that transform recieved acoustic pressures intoo electrical voltages or currents, which may be amplified and conditioned for application to metres, tape recorders, speakers, earphones, sound cards.

Question 14

The absolute auditory threshold

Answer 14

In an animal it is the minimum recieved sound level at which a sound with particular frequency and other properties can be perceived absence of significant background noise.
Low threshold indicates high sensitivity and vice versa.

Question 15

Evolution of sound use by cetacean

Answer 15

Primarily is about development of

Question 16

purposes cetaceans use sound

Answer 16

Detect predators
Detect prey
Orientate, navigate, explore environment
Detect and decode calls from conspecifics
- mother/calf cohesion
- group cohesion
- individual recognition

Question 17

Signal types

Question 18

3 categories odontocete sound falls into

Answer 18

Whistles
Bangs
Pulses or Clicks

Question 19

Echolocation is

Answer 19

The process by which an organism projects acoustic signals in order to obtain a sense of its surroundings from the echoes it receives.

Question 20

Sonar

Answer 20

Sonar, ecolocation and the term biological sonar

Question 21

A priori

Answer 21

It was assumed a priori that the sound source of some or all odontocete sounds was the larynx.
It was a logical sound source as most other mammals including many echolocating bats produce sound from the larynx
It is the nasal where these sounds are produced.