What Is Echolocation The analysis by an animal of the echoes of its - - PDF document

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Bat Echolocation, Call Structure & Influence of Habitat

What Is Echolocation

• The analysis by an animal of the echoes of its own

emitted sound waves John D Altringham, Bats Biology and Behaviour

• Used by micro-bats (old currency!) in order to

navigate and find food (usually!)

• Sound travels through air at a constant speed

(340ms)

• A bat is listening for how long it takes for sound

to come back relative to when it was emitted

• It’s an ‘adaptable tool’
• Social Calls are nothing to do with echolocating

= Communication

An Overview

• Echolocating bats emit:
• high frequency sounds (ultrasonic) (tone)
• repeated constantly (repetition rate)
• on the upstroke of each wing beat (rhythm)
• comprising of different components within each isolated

call (or pulse)

• Influences:
• physical capabilities of the bat (e.g. wing loading)
• large bats = slower/lower : small bats = faster/higher
• habitat
• feeding (equiv to 50 - 200 pulses per sec)

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Call Structure

• Can comprise of a FM component and a CF

component

• Broadband = FM bats/components
• Short sweep down through frequencies (iow the frequency alters

during the call)

• Good for detail at close range & accuracy
• Narrowband = CF bats (almost!)/components
• Longer call covering narrower frequency range (iow the frequency

remains constant and the pulse lasts longer)

• More effort concentrated in one area over longer time
• Good for distance
• Horseshoe bats & Doppler shift (i.e. the pitch of a sound rises or drops

as a sound source moves)

Freq Time Closed Edge Open Fast Wingbeat Slow Slow Flight Speed Fast Detail Information Distance Myotis spp. Plecotus spp. Pipistrellus spp. Nyctalus spp.

Habitat Influences

• Open Space
• Use lower rep rates
• Use long range echo’, loud, lower frequency & regular
• Have a longer CF component
• Change direction less often
• Flies faster = less wing beats (e.g. Nyctalus)
• Clutter
• Use faster rep rate
• Shorter & quieter calls
• Use FM
• Flies slower = more wing beats (e.g. Natterer’s)
• Edge Habitat?

Measuring Call Parameters

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Harmonics Attenuation Search Phase Calls Better for ID

Closed Edge Open Habitat Influence on Bat Call ID Nyctalus Noctule Leisler’s

As the bat moves to an Open setting the call structure becomes more distinguishable

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Bat Echolocation – Species ID

Pipistrellus spp. Nyctalus spp. Myotis spp.

• All fast rep rates
• All FM bats (no CF tail) = dry clicks
• Very difficult to ID to species level,

however…

• Sometimes you can get there - almost!

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Brown long-eared

• Late emergers
• Very quiet echolocator
• Sometimes go acoustically ‘dark’
• You need to be close to the bat
• Harmonics

Others

• Horseshoe spp
• Barbastelle
• Serotine