Echolocation Flashcards
Echolocation
• Use echoes of sounds produced to locate objects
Who does echolocation?
– Chiroptera – navigation & hunting – Odontoceti – navigation & hunting? – Soricomorpha – navigation – Afrosoricida – navigation – Rodentia – navigation
• Water is much denser than air
– Sound travels 4X faster in water
– Sound attenuates more rapidly in air
• Aquatic echolocating mammal
– Signals transmitted farther and return faster
– Less energy used for signal of given intensity
Echolocation calls can be described in terms of
time, frequency, and intensity
Echolocation in bats
• Brief pulses of sound •Frequency varies widely among species • Intensity (decibels) • Bandwidth (breadth of frequencies produced)
Range Limits
• Echolocation is a short-range system in air
– Targets detected at close range
– Requires slower, more maneuverable flight
High-Frequency Sound
• Rapidly attenuated in air
• Why use high frequencies?
– High frequency = short wavelength
– Objects equal in size to wavelength reflect that wavelength well
– Low frequency sounds have long wavelengths
• Tend to bend around small objects instead of being reflected
How do bats distinguish incoming from
outgoing calls?
- Duty cycles (high or low)
2. Self deafening
• Clicks
– Produced in nasal passages in odontocetes
– Produced with tongue in two genera of pteropodids
• Vocal signals
– Produced in larynx in most echolocating
chiropterans and soricomorphs
– Low duty cycle approach
- Produce signals small percentage of time
* Do not broadcast and receive signals simultaneously
– High duty cycle approach
• Produce signals larger percentage of time
• Produce pulses and receive echoes simultaneously
• Doppler-shifted echoes
-Distinguish echo by frequency
Self-Deafening
• Middle and inner ear are insulated from the rest of
the skull
• Two ear muscles dampen sounds – Tensor tympani • Changes tension in tympanic membrane – Stapedius • Changes contact between stapes and oval window
• Bat echolocation pulses emitted via:
– Nose • Members of Nycteridae, Megadermatidae, Rhinolophidae, Hipposideridae, and Phyllostomidae – Mouth • All the others
Faces, Ears, and Echolocation
• Mouth emitters use lips like megaphones
• Noseleaves and horseshoes focus sound
• Tragus
– Sound localization
Both echolocation and flight contributed to
evolution and diversity of bats (>1000
species)
• Echolocation calls probably derived from
vocal communication
Evolution of Echolocation Hypothesis: • Echolocation-first hypothesis – • Flight-first hypothesis – • Tandem-evolution hypothesis –
– Bat ancestors were small, nocturnal gliders
– Bat ancestor capable of powered flight
– Echolocation and flight evolved together
• Evidence for Flight First Hypothesis
– Early Eocene bat Onychonycteris could fly:
– Onychonycteris could not echolocate
• Many nocturnal moths have “ears”
– “Ears” are on thorax
– Sensitive to wide range of frequencies
– Aid detection of bat ultrasonic pulses
• Some moth species have sound-producing
organ on thorax
– Produce ultrasonic clicks
– Interferes with bat signals/echoes
Coevolution
– Bats prey on nocturnal moths
– Moths responded by detecting bats’ signals • Avoidance maneuvers • Jamming bat echolocation – Bats responded by: • Using allotonic frequencies • Lower duty cycles
Sound in Cetaceans
Two basic types of sounds
– Narrowband continuous tones (whistles)
– Broadband clicks (audible to humans)
Echolocation in Cetaceans • Types of biosonar – Active sonar • – Passive sonar • – Ambient noise imaging •
• Typical echolocation – hearing echoes of emitted
sound pulses
• Hearing sounds without producing sounds
• Ability to “
see
” underwater with sound
• Where are echolocation clicks produced?
in cetaceans
– Upper nasal passages ventral to blowhole
– Bilateral phonic lip/dorsal bursae (PLDB)
complex
in cetaceans • Melon serves to focus sound pulse into beam – • Sperm whales have single large PLDB –
– Forms an “acoustic lens” that shapes the beam
– PLDB anterior to spermaceti organ and junk
Echolocation in Cetaceans
•Rapid bursts of clicks (called creaks) may
be analogous to terminal buzz in bats
•Intense blasts of sounds (called bangs)
may disorient or stun prey
Cetacean Hearing
• Bullae are insulated from skull by sinuses
–
• Thin region on posterior dentary (pan bone)
–
– Sinuses contain oil-mucus-air emulsion
– Acts as acoustic window
• Shrews may echolocate for
target
detection
• Tenrecs echolocate by
tongue clicks
• Some rodents produce ultrasonic sounds
– Probably for communication
Pinnipeds
– No direct evidence for echolocation
• Sirenians
– Complex, single-note calls
– No clear evidence of echolocation (target
detection)
