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746 Lecture 2

746 Lecture 2. Echolocation in Bats. Aim. Outline properties of sound Hunting behaviour of bats Types of Echolocation sounds Specialisation of Ear CNS Auditory behaviour of moths. Properties of sound. Sound is wave of rarefaction and compression has speed 330m/s, c = f * l

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746 Lecture 2

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  1. 746 Lecture 2 Echolocation in Bats

  2. Aim • Outline properties of sound • Hunting behaviour of bats • Types of Echolocation sounds • Specialisation of • Ear • CNS • Auditory behaviour of moths

  3. Properties of sound • Sound is wave of rarefaction and compression • has speed 330m/s, c = f * l • wavelength l - determines whether objects will reflect or diffract sound • frequency f • intensity - • measured in dB

  4. Harmonics • multiples of frequency • usually less intense

  5. Hunting behaviour of bats Taphozous Pipistrellus Megaderma Hipposideros

  6. Echolocation sounds • all bats use “ultrasonic” sounds • CF - • constant frequency • long tone, often with some harmonics • velocity • FM - • frequency modulated • short burst of sound • range determination

  7. CF in free air

  8. FM • near ground or vegetation

  9. CF-FM • CF then droop • depends on place

  10. Landing - Rhinopoma

  11. catching - Myotis

  12. What will bat hear? • itself ? • reflection ? • quieter • more variable? • Doppler shift in frequency ?

  13. Doppler shift (i) • emitted sound

  14. Doppler shift (ii) • Reflected sound sometimes in phase and sometimes out of phase in out

  15. Doppler shift (iii) • If reflected and emitted sound have similar intensity, Doppler echo will generate beats • Production of new frequency from old!

  16. Doppler summary • New frequency – depends on ratio of outgoing sound and incoming sound • Incoming sound is reflected off ground/trees • Difference in frequency therefore tells how fast the bat is flying • fnew = fout (v + s)/v • v speed of sound • s speed of bat

  17. Echoes • From stationary insect • head on- symmetrical • sideways on asymmetric Echoes from fixed Tipula

  18. Moving Tipula

  19. Summary so far • Ultrasonic sound • CF FM • habitat dependent • Echoes return information • moving insects • time to return • frequency spectrum • shifted • broadened

  20. Behaviour to physiology • Specialisation of • Ear • CNS

  21. Human ear

  22. Bat ear (i) • Large pinnae • directional sensitivity • extra gain • Tragus • elevation

  23. Bat ears (ii) • middle ear muscles • reduce sensitivity while emitting? flying bat

  24. Bat ear (iii) • More of cochlea tuned to high frequencies than in other mammals

  25. Tuning curve • auditory nerve • tuned to “best” frequency of emitted CF • actually to just above (Why?)

  26. CF lowered in flight • Doppler shift as fly towards object raises return sound frequency

  27. CNS outline AC IC CN

  28. CNS • Auditory cortex neurons sensitive to pairs of stimuli • load/quiet • delay time crucial • time map

  29. mechanisms of delay • coincidence detection • inhibition of sound • delay line • slow axon • synapse • control with vocalisation • inferior colliculus neurons respond only 30/40ms after vocalisation

  30. Summary - audition • Ear and CNS both highly specialised • more sensitive to ultrasonic frequencies • achieve increase in sensitivity to echo • respond to pairs of stimuli

  31. Moth Auditory system • 2 axons in ear low and high threshold

  32. Behaviour • low threshold - fly fast • high threshold - stop flying and fall • ?like a leaf • Emit clicks - • jam bat sonar - phantom echo returns at wrong time? • warning of unpalatability? • moths (Euproctis) emit clicks in mimicry of distasteful moths

  33. Conclusion • co-evolution of bats and moths • defence reactions • escape • auditory camouflage • auditory

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