Transcript bats2
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 wavelength l - determines whether objects will reflect or diffract sound frequency f intensity measured in dB Harmonics multiples of frequency usually less intense Hunting behaviour of bats Taphozous Pipistrellus Megaderma Hipposideros 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 CF in free air FM near ground or vegetation CF-FM CF then droop depends on place Landing - Rhinopoma catching - Myotis What will bat hear? itself ? reflection ? quieter more variable? Doppler shift in frequency ? Doppler shift (i) emitted sound 1.5 1 0.5 0 0 -0.5 -1 -1.5 200 400 600 800 1000 1200 1400 1600 Doppler shift (ii) Reflected sound sometimes in phase and sometimes out of phase 4.5 1.5 3.5 0.5 2.5 -0.5 1.5 -1.5 0.5 -2.5 -0.5 0 -1.5 200 400 600 800 1000 1200 1400 1600-3.5 -4.5 in out Doppler shift (iii) If reflected and emitted sound have similar intensity, Doppler echo will generate beats 1.5 6.5 0.5 5.5 4.5 -0.5 3.5 -1.5 2.5 1.5 -2.5 0.5 -0.5 0 1000 2000 3000 4000 -1.5 Production of new frequency from old! -3.5 5000 -4.5 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 Echoes From stationary insect head on- symmetrical sideways on asymmetric Echoes from fixed Tipula Moving Tipula Summary so far Ultrasonic sound CF FM habitat dependent Echoes return information moving insects time to return frequency spectrum shifted broadened Behaviour to physiology Specialisation of Ear CNS Human ear Bat ear (i) Large pinnae directional extra gain Tragus elevation sensitivity Bat ears (ii) middle ear muscles reduce sensitivity while emitting? flying bat Bat ear (iii) More of cochlea tuned to high frequencies than in other mammals Tuning curve auditory nerve tuned to “best” frequency of emitted CF actually to just above (Why?) CF lowered in flight Doppler shift as fly towards object raises return sound frequency CNS outline AC IC CN CNS Auditory cortex neurons sensitive to pairs of stimuli load/quiet delay time crucial time map mechanisms of delay coincidence detection inhibition delay of sound line slow axon synapse control with vocalisation inferior colliculus neurons respond only 30/40ms after vocalisation Summary - audition Ear and CNS both highly specialised more sensitive to ultrasonic frequencies achieve increase in sensitivity to echo respond to pairs of stimuli Moth Auditory system 2 axons in ear low and high threshold 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 Conclusion co-evolution of bats and moths defence reactions escape auditory auditory camouflage