746 Lecture 2 Echolocation in Bats

Aim nOutline properties of sound nHunting behaviour of bats nTypes of Echolocation sounds nSpecialisation of u Ear u CNS nAuditory behaviour of moths

Properties of sound nSound is wave of rarefaction and compression has speed 330m/s, c = f * wavelength  - determines whether objects will reflect or diffract sound nfrequency f nintensity - u measured in dB

Harmonics nmultiples of frequency nusually less intense

Hunting behaviour of bats Taphozous Pipistrellus Megaderma Hipposideros

Echolocation sounds nall bats use “ultrasonic” sounds nCF - u constant frequency u long tone, often with some harmonics u velocity nFM - u frequency modulated u short burst of sound u range determination

CF in free air

FM nnear ground or vegetation

CF-FM nCF then droop ndepends on place

Landing - Rhinopoma

catching - Myotis

What will bat hear? nitself ? nreflection ? u quieter u more variable? u Doppler shift in frequency ?

Doppler shift (i) nemitted sound

Doppler shift (ii) nReflected sound sometimes in phase and sometimes out of phase in out

Doppler shift (iii) nIf reflected and emitted sound have similar intensity, Doppler echo will generate beats nProduction of new frequency from old!

Doppler summary nNew frequency – depends on ratio of outgoing sound and incoming sound nIncoming sound is reflected off ground/trees nDifference in frequency therefore tells how fast the bat is flying nf new = f out (v + s)/v u v speed of sound u s speed of bat

Echoes nFrom stationary insect u head on- symmetrical u sideways on asymmetric Echoes from fixed Tipula

Moving Tipula

Summary so far nUltrasonic sound u CF FM u habitat dependent nEchoes return information u moving insects u time to return u frequency spectrum F shifted F broadened

Behaviour to physiology nSpecialisation of u Ear u CNS

Human ear

Bat ear (i) nLarge pinnae u directional sensitivity u extra gain nTragus u elevation

Bat ears (ii) nmiddle ear muscles u reduce sensitivity while emitting? flying bat

Bat ear (iii) nMore of cochlea tuned to high frequencies than in other mammals

Tuning curve nauditory nerve u tuned to “best” frequency of emitted CF u actually to just above (Why?)

CF lowered in flight nDoppler shift as fly towards object raises return sound frequency

CNS outline AC IC CN

CNS nAuditory cortex neurons sensitive to pairs of stimuli u load/quiet u delay time crucial u time map

mechanisms of delay ncoincidence detection u inhibition of sound u delay line F slow axon F synapse ncontrol with vocalisation u inferior colliculus neurons respond only 30/40ms after vocalisation

Summary - audition nEar and CNS both highly specialised u more sensitive to ultrasonic frequencies u achieve increase in sensitivity to echo u respond to pairs of stimuli

Moth Auditory system n2 axons in ear low and high threshold

Behaviour nlow threshold - fly fast nhigh threshold - stop flying and fall u ?like a leaf nEmit clicks - u jam bat sonar - phantom echo returns at wrong time? u warning of unpalatability? u moths ( Euproctis ) emit clicks in mimicry of distasteful moths

Conclusion nco-evolution of bats and moths ndefence reactions u escape u auditory camouflage u auditory