Chapter 25 : Autocommunication 5/5/11 Lecture #25 Chapter 25 : Autocommunication 5/5/11

Key dates Final exam questions will be posted Friday by noon Wiki projects are due Tuesday, May 10th at midnight Last class on Tuesday Final exam Thursday, May 12th 8 am

Today Echolocation basics Echolocation in bats Open-site foragers Gleaners Hawkers and fishers Echolocation in cetaceans

Autocommunication Echolocation = biosonar Electrolocation Emit pulses of sound Electrolocation Determine environmental information about nearby objects What is its size and shape? What is it doing? Where is it now and where might it be going?

Autocommunication Not technically communication Shaped by same design factors such as…???

Autocommunication Not technically communication Shaped by same design factors Shape signals to adjust for - Efficient emission - Propagation and distortion - Reception

Why is environmental signaling simple or absent much of time? Do senders rarely reap benefits of communicating more complex information (benefits go to receivers)? OR Is it too difficult and expensive to encode and extract information?

Autocommunication should represent perfect communication Sender and receiver are the same individual - NO CONFLICT Receiver should be ideal receiver - extract as much information as possible Sender should pack as much information in as possible

Autocommunication should be perfect test case So are autocommunication signals more complex than those between individuals? (no game) Or are they just as simple because it is too difficult to encode and extract info?

Echolocation Simple echolocation More sophisticated echolocation Oilbird Lesser tenrec Shrew Oilbird: http://venworld.wordpress.com/2008/10/01/the-guacharo-of-caripe/ http://planet.uwc.ac.za/nisl/biodiversity/loe/page_205.htm http://sardinebaybocas.com/Dolphin.html

Echolocation information Environmental information: Object location (range, angle) Object identity (shape, texture composition) Relative velocity and trajectory May be trade offs btn object properties Accuracy about one may require uncertainty in another

Detecting targets at distance Outgoing signal must be loud enough to produce echo that is above ambient noise Signal must be emitted enough of time that sound beam will strike target Best if work at single frequency All energy at that frequency Tune receiver to that frequency

Echo intensity  1/distance4 Echo  1/distance2 Signal  1/distance2

Scattering summary Fig 2.6 Bigger objects, more scattering. Shorter wavelength, more scattering. For 1 kHz, wavelength is 33 cm. So for objects < 5 cm, Rayleigh and objects>3.3 m, simple scattering. In between get complex scattering pattern. Fig 2.6

Other factors Want frequency that can emit with highest intensity Maximum reflection when wavelength < object For 1cm insect, minimum freq is 34 kHz For 10 cm fish, minimum freq is 3 kHz But high frequencies absorbed by medium So optimum is in between Frequency = c / wavelength = 340 m/s / .01 m = 34 kHz

Echolocation signals Assumes bat signal of 110 dB at 60 kHz directed at 1.9 cm target located 3 m away If sound goes from 0.1 m to 3 m then spreading loss is 10 log ((.1/3)^2)) = -30 dB but looks like only -15 dB on returning - I think absorption and spreading loss are switched Outgoing absorption is about 5 dB?? But returning absorption is more like 30 dB Lose 20 dB in echo (factor of 100

Echolocation signals - optimal frequency is balance of production and propagation Assumes bat signal of 110 dB at 60 kHz directed at 1.9 cm target located 3 m away If sound goes from 0.1 m to 3 m then spreading loss is 10 log ((.1/3)^2)) = -30 dB but looks like only -15 dB on returning - I think absorption and spreading loss are switched Outgoing absorption is about 5 dB?? But returning absorption is more like 30 dB Lose 20 dB in echo (factor of 100

Pulse duration Send out pulse of sound Need to leave silence to hear echo Time between pulses (trep) = 1 / frequency Duty cycle = fraction of time are calling per pulse = tpulse / trep tpulse trep

Time for echo to return Sound velocity = distance / time Return time = distance / velocity Distance = Velocity * time Distance to object

Time for echo to return Signal Echo techo

Minimum distance probed determined by pulse width Signal tpulse Echo Have to wait for outgoing pulse to end before can hear echo techo = tpulse

Minimum distance probed determined by pulse width Signal tpulse Echo Pulse width Distance (m) 0.1 s 17 m 0.01 s 1.7 m 0.001 s 0.17 m techo = tpulse

Maximum distance probed determined by pulse repetition Signal tpulse techo = trep Echo Want to receive echo before next pulse begins

Maximum distance probed determined by pulse repetition Signal tpulse Echo techo = trep Freq (Hz) Pulse rep Distance 20 0.05 8.5 m 100 0.01 1.7 500 0.002 0.34

Determining target distance Can use echo amplitude Also affected by size and shape of target Can use delay time, techo Possible that moth only reflect sound when its wings are perpendicular to sound (top and bottom of flap) So only get part of pulse returned If label pulse with frequency, will know which part of pulse is reflected

Uncertainties Constant frequency pulse has errors tactual tmeasured

Frequency modulation is more accurate Can compare correlated part of the pulse tactual Can decrease range error from 2.7 to 0.16 cm tmeasured

Doppler demonstration #2 Doppler demonstration http://www.walter-fendt.de/ph14e/dopplereff.htm

Doppler shift Perceived frequency depends on relative velocity of predator and prey If moving towards, frequency is higher (minus sign) If moving away, frequency is lower (plus sign)

Doppler shifts As bat flies towards moth, echo will be doppler shifted higher Also will arrive sooner than if bat is stationary Can linearly modulate emitted pulse Frequency Period Inverse frequency So modulation of pulse period (making it shorter as go) produces most accurate and predictable shift (most like outgoing pulse) which is good for comparisons and makes for Doppler tolerant signal

Determining target angle If focus outgoing beam to narrow angle, then know at what target angle get a response High resolution May miss insect Angle may vary with frequency Can also use directional sensitivity of ears Arrival time delay

Emitted beam has angular variation Compensate with angular response of ears!! Emitted beam Ear sensitivity Combination

Determining target properties Distinguish echoes from background (clutter) and target prey Echo amplitude related to target size -- if also know target range (time delay) All aerial targets will reflect No info on what target is made of Most aquatic targets will absorb and may resonate - can use to discriminate what target is made of

Determining target velocity and trajectory Hard to do with frequency modulated pulse Which outgoing frequency matches which incoming frequency?? Using constant frequency signals, can get better estimate of Doppler shifts Get more cycles of sound on target

Tradeoff Frequency modulation Constant frequency Best for estimating range Constant frequency Best for estimating velocity Tough to estimate both range and velocity at same time Decreased error for one increases error for other Animals must choose which to optimize

Echolocation in bats 800 species of bats Megachiroptera Eat fruit, nector or flowers Rely on nocturnal vision (one rudimentary echolocator) Microchiroptera Feed on insects, small verts, blood or fruit/flowers Use echolocation to forage and navigate

Open-site foragers : insectivores Not much clutter to worry about Emit broad beam of sound through mouth (60-90 deg) Loud intensities 100-120 dB SPL As intense as can be w/o collapse blood vessels Three phases of foraging Search Approach Buzz

http://www.vleermuizen.be/GewoneDwergvleermuisFoto.html

Decreases pulse width as get closer to target Always stay below echo overlap pulse width When very close, stop echolocating (4-10 cm)

Open-site foragers

Range Pipistrelle is small bat Larger bats use lower frequencies Use 30-50 kHz to search Can detect prey > 0.2 mm Maximum range 1.5-2 m Larger bats use lower frequencies Either to find larger prey Or to find prey at larger distance since not as agile

Higher frequency is used at shorter range, requires shorter pulse duration Higher frequencies are more quickly attenuated and so they sample closer to the bat. At these shorter distances, echos reach bat more quickly and so pulse duration has to be shorter to avoid pulse - echo overlap. Px are the different Pipistrelle species

Bats are pretty good at this Time to catch an insect = 0.5-1 s Catch insect every 4 s Capture efficiency = 30-40% for moths = 60-70% for mosquitos

Bat - Gleaners Forage from close to surfaces Foliage, barns Lots of clutter from larger reflecting surface To prevent being overwhelmed use low sound intensity Whispering bats Narrow beam emitted from nose

Insectivorous bats Mouth emission Frugivore Nose emission Predators Spiders, lizards Vampire doves, parrots Fishing hawks insects gleans insect

Detect moving target against fixed background Need to determine angle of moving target Gleaners have high angular accuracy 1.5-2º Can also perceive fluttering motion in reflected spectrum Can also detect sounds from prey and odors

Hawkers and fishers Hang in one location scanning for prey and then fly in to capture Patrol close to vegetation and capture moving insects Fishers detect disturbance on water surface Need to then predict where fish will be when go to catch it (sonar does not enter water)

Fishing bats and finding water

Hawking by Rhinolophus Use high duty cycle constant freq pulses with FM sweeps on end Use very high freq so can detect small targets Doppler shifted echoes from prey movement Want wavelength about size of animal 83kHz = 4 mm object If insect moves 1 m/s then freq shift of 484 Hz vs 83kHz

Cochlea has hair cells supported by basilar membrane http://www.pc.rhul.ac.uk/staff/J.Zanker/PS1061/L5/inner_ear.gif Basilar membrane responds to high, med and low freq as move down the cochlea - tonotopic map

CF bat ears Normal mammalian cochlea has tonotopic map CF bat cochlea has a “fovea” Region where tonotopic map is expanded 100 90 80 70 60 50 40 30 20 10 100 90 80 70 68 66 64 62 60 50 40…

Bats are close to ideal receivers Design ideal signals FM sweeps which are Doppler-tolerant Likely use comparison of phase shifts in echoes vs emitted calls to further improve ranging (cross correlation) Gives minimal error possible 0.007 mm May help with target identification

Why is environmental signaling simple or absent much of time? Do senders rarely reap benefits of communicating more complex information (benefits go to receivers)? OR Is it too difficult and expensive to encode and extract information? Bats use most complex signals possible

Echolocation in cetaceans Predatory species echolocate Toothed whales Porpoises Challenges of aquatic habitat Velocity 4.4x greater; Wavelengths 4.4x longer Need higher frequencies for same sized target (vs air) But since larger animals, targets are larger so it’s a wash

Other constraints Faster sound velocities require shorter pulses to prevent pulse - echo overlap 0.05-0.1 ms This is even shorter than needed so don’t have to shorten as get closer to an object as bats do Low attenuation so good signal propagation Dolphin can detect 2 cm target at 73m Bat needs to be 2-4 m to detect it

How do cetaceans create pulses? Porpoise emits through head and detects through jaw Porpoise pulse and power spectrum Dolphin detection is only 6-8dB worse than an ideal receiver Minimal range error < 1 cm

Cetacean pulse production Sperm whale breathes through left nostril and makes pulses with right nostril

Conclusion Both bats and cetaceans are close to ideal receivers So rest of animals could send and extract more information than they do Likely conflicts of interest Within bats, they do not share their environmental info with other bats Have own personal frequencies

One exception to all of this Humans We share all kinds of environmental information (and other information) with each other Perhaps we will find other animals do better than we think: parrots, corvids, elephants, higher primates and cetaceans

Congratulations!! I can’t believe we read the WHOLE book There is still more to learn about animal communication