Mammals and Sound

Define communication

The process of exchanging information through scent, sound, visual displays, and more.

Why do mammals communicate?

• courtship

• warnings

• food

• territorial defense

• social play

• parental care

Describe what sound is

Sound is a vibration that carries through air, water, or ground. The vibrations cause a chain reaction of compressions (high pressure) and rarefactions (low pressure) that radiate outward from the source. When these waves reach the ear, the vibrations are converted into signals that the brain interprets as sound. 

It moves fastest to slowest through ground → air → water 

What kind of sound is coming from each of these numbers and give an example for each of an animal that makes them.

1. ultrasonic sound waves (dolphins + bats)

   1. beyond human hearing

2. audible sound waves (humans)

   1. sounds of daily life, from speech and music to environmental sounds

3. infrasound waves (elephants)

   1. imperceptible to humans but can carry over long distances and through various mediums

difference between the two?

narrow bandwith + high amplitude = short, high-pitched sound

broad bandwith + low ampltitude = long, low-pitched sound

attenuation

the reduction in the intensity or strength of a sound wave as it travels through a medium or is blocked by materials

High frequency sounds attenuate _____ over a long distance.

Low frequency sounds attenuate _____ over a short distance.

Why?

High frequency sounds attenuate more over a long distance.

• more likely to reflect off of (bounce off) something

Low frequency sounds attenuate less over a short distance.

• more likely to propagate (go through) something

Advantages and disadvantages of using sound as a communication method.

Advantages	Disadvantages
Works when visibility is low	Reveals position to predators or rivals
Can travel around obstructions	Noise can cover up message
Allows for complex messages	Can be energetically costly
Quick transmission	Limited directionality
Can be detected from a distance	Info can get lost over long distances

Low-frequency versus high-frequency sounds

Low-Frequency (elephants)	High-Frequency (bats)
Large body size = low-pitched sound	Small body size = high-pitched sound
Sound is used to communicate	Sound is used to find prey
Sound travels farther	Sound travels short distances
Live in open areas = less likely to reflect	Live in cluttered areas = very likely to reflect

Explain how elephants detect low-frequency vibrations through the ground and why this is vital to their social communication.

Elephants feel them with their trunks and feet, which travel up the trunk or leg into the brain, where the sound is interpreted. They will use these calls to warn others of predators.

Echolocation in bats vs. odontocetes

Bats	Odontocetes
Use a series of calls	Use a series of clicks
High frequency - travels farther in the air	Low frequency - travels farther underwater
Varied calls	Invariable calls
Terminal buzz present	Terminal buzz present

Identify and explain the stages of a bat’s echolocation call during foraging.

Constant Frequency (CF) - Searching

• constantly calling, waiting for the call to bounce off of prey

• not detailed, low-bandwidth, constant

Frequency Modulation (FM) - Approach

• CF bounced off of prey

• uses to approach and begin to zero in on prey

• detailed, high-bandwidth, varies

Terminal Buzz (TB) - Kill Shot

• zero in and swooping to catch prey

• very short, frequent calls

• very detailed, high-bandwidth, constant

Advantages/disadvantages of echolocation

Advantages	Disadvantages
Efficient hunters	Energy cost
Reduces chances of colliding with things	Only bits of info at a time - low resolution
Unique niche = little competition	Limited sound range

Recognize key insect adaptations that allow them to detect and respond to bat echolocation.

• Moths hear the bats coming and produce their own ultrasound back at the bats to disguise their location by “jamming the bat sonar”

  • sound-producing structures on their thorax or the tip of their abdomen/genitals

• Batesian mimicry: send messages to bats telling them they taste bad, some do taste bad, others are bluffing

  • bats are very picky so this works