Bat Echolocation

• producing sound and being able to hear is vital for navigating • removed eyes = fine • plugged ears = not fine • tubes in ears = fine • plugged tubes in ears = not fine • tapped mouths shut = not fine

• animal rights activist • using theory determined that they use ultrasound and coined the term echolocation • used an ultrasound detector made by Peterson • discovered that bats hit or touched a wire more if it was thinner (<0.5mm) • as bats got closer to target their pulse rate increased and pulse duration decreased

• use delay between pulse and echo • trained bats to land on one of two platforms • used speakers to play back a phantom echo

• Frequency modulated (FM) component: useful in forests - Constant frequency (CF) component: useful in open spaces

• FM bat - produce broad band signal 100 khz to 25 khz

• use time delay from pulse to echo • FM bats use frequency analysis and time analysis • echo intensity: far away if weak • frequencies returned: high frequencies don’t travel far

• the loudness of the echo determines the subtended angle - problem: could be small and close or far away and large

• using a combination of distance info (delay) and subtended angle (amplitude)

• location in the horizontal plane - by binaural cues

• location in vertical plane - moving ears in various positions

• CF-FM bat • pulses with long constant frequency then rapid downward FM sweep • sensitive to 83 KHz

• if the predator and prey are still, the frequency will return the same • if predator and prey are moving towards each other, the frequency will increase • problem: returning frequency could be outside of species specific frequency range

• when moving forward they lower the frequency emitted so the returning frequency will be within the specific range • bats placed on swing and recorded pulses • also means that the loud pulse emitted is out of their range and they avoid deafening

• increase in sensitivity to a narrow range of frequencies - results from a range of adaptations

• CF-FM bat with several harmonics - harmonic at 60 Hz is the loudest

• pulse = noise - echo = signal

• analyze the doppler shift echoes to determine if the bat is gaining or not

• position of the wing of prey • if wing is ‘close’ to bat will produce a higher frequency • if wing is horizontal there is a smaller surface area for the echo to bounce off of, decrease in amplitude

• uses CF component to determine flutter while hanging still - uses FM component for tracking and capture

• large pinna and tragus which allows them to detect faint echoes • nose leaves to direct sound coming from nose

• can no longer differentiate where sound is coming from

• abrupt thickening and lengthening where the species specific CF component frequency is cast • results in expanded region for preferred frequencies and increase in sensory neurons in critical range • (basilar membrane thins and widens at low frequency end)

• cells are stimulated by the movement of the basilar membrane • pressure causes them to bend and the tip links pull open K channels • get K influx that depolarizes the cell • causes Ca influx • then K efflux to repolarize • hair cells don’t generate an action potential, they release NT

• determines how weak a stimulus can be presented and still be heard • at species specific frequency they have a low threshold to be able to detect quiet echoes