4.1 Sound Generation and reception

What are the main steps in sound generation?

Generation of vibrations, modification of vibrations, and coupling the vibrations to the medium.

Solid - solid types

Percussion, stridulation, buckling, tremulation

Percussion examples

woodpeckers, rattlesnakes, stamping, etc

What is stridulation?

A sound production method in crickets using a file and plectrum.

Buckling

Bending and release

tremulation

movement of entire body > vibrations

Fluid media

Surface waves, pulsation, fanning, fluid compression, streaming

Surface waves/ripples comes from what

Percussion

- can be more subtle

Pulsation

use of swim bladder in fish

fanning

with wings, fins, etc.

- humming birds

Fluid compression

Quick change in local pressure

- sonic boom

- cavitation if in water

Streaming

usually birds in flight > whistling or humming from the motion

What does streaming do

announce/signal presence of animal

- pigeon

Aerodynamic vibrations/sounds

solids are immobile, but fluids vibrate

- hisses, whistles

Vocalizations

Solid (organ) and fluid vibrate

types of vocalization production

Tube, valve, air supply/storage

*Larynx

*Syrinx

larynx

contralateral organization

- Mammals, reptiles, amphibians

Syrinx

Ipsilateral organization

- birds

Solutions to constraints

Modify a given frequency

- something WILL get through

Modifying a given frequency

Positive interference and negative interference

Positive interference

amplification by resonance

Negative interference

Reduction by filtering

What is active space

the space where it's physically moving

Active space relates to what

the reciever

What is the Acoustic Adaptation Hypothesis (AAH)?

propagation loss and increased detection in noise

What kind of theory is the Acoustic Adaptation Hypothesis (AAH)?

An optimality theory

- every species has optimal adaptations to environment

Is maximizing propagation and active space always at the advantage of the sender?

1. between conspecifics/competing species: maybe

2. prey (avoiding preds): no

Degredation

Sound usually dies as soon as you stop producing it

What is degradation used for

can be used by receivers/preds/competitors to judge distance from source (sender)

What is used to assess degradation

Gradients to judge physical distance

Degradation and distance

closer: easier to figure out what it is

farther: harder to differentiate, lose info

What are the four types of degradation in sound propagation?

1. Attenuation 2. Distortion of frequency pattern 3. Distortion of temporal pattern 4. Masking by noise

Degradation - attenuation

Spreading loss and refraction

Spreading loss

Pressure is lost over time

Where does sound move faster

In warmer layers of air

in high pressure

With a current

What can cause refraction

Boundaries

- between zones of different temp, pressure, currents

Refraction of sound waves for a receiver close to ground on hot day

Hot ground pushes sound up into colder air

- sound shadow

what is a sound shadow

Analogical to a "blind spot"

Refraction of sound waves for a sender close to the ground on a clear night or at dawn

Temperature inversion (ground cools)

- dawn chorus

- increased active spots

Dawn effect

ground and air are cooler = better for sound

Refraction of sound waves near ground due to wind

wind pushes it

- screaming against the wind vs with it

Refraction of sound waves in a forest

Canopy is your surface

- where the heat is

Forest conditions: high

Warmer and dryer; more wind

Forest conditions: low

cooler and damper; less wind

- protection from wind at ground level can be an advantage

Is ground refraction favourable

at least during the day, yes

- at dawn can change with temperature inversion

where does sound travel farther

in colder air

- early morning singing

Distortion of frequency pattern

heat loss, scattering, boundary effects

Distortion of temporal pattern

Reverberation, modulation, dispersion

Masking by noise

background noise, noise from conspecifics, etc