Chapter 6: Vocal anatomy, acoustic communication and echolocation

Communication

Acts / structures that affect the behaviour of other organisms and have evolved because of those effects

➢Simple communication: In organisms that lack nervous system, without cognitive abilities, e.g. bacteria

➢Non-informative communication: Lack of cognition, e.g. tungara frogs

➢Passive communication: Swim movements, splashes, exhaling, bubbles, flipper strokes ..

➢Auto-communication: Echolocation

➢Informative communication: Including cognition: alarm calls, waggle dance, language, but also aerial displays like breaching in humpback whales or bubble blowing in bottlenose dolphins ..

Acoustic communication in the sea

Acoustic sensory modality is favoured:

➢Speed of sounds ca 5 times faster than in air, 1500m/s (air 340m/s)

➢Compared to light, which only travels 100m in water - 10km in air

➢Sound travels >100km in water - 1km in air

Sound production marine mammals

Aquatic marine mammals

(cetaceans, sirenians, phocids, walrus) specialised in sound communication & exploration of sea= 2-3 x more auditory versus optic nerve fibres (than land mammals)!

Semi-aquatic marine mammals

(otariids, sea otter, polar bear) communicate mainly in airbut phocids in air and underwater

Larynx

Pinnipeds: well developed Larynx, used for respiration and sound production

Differences between:

➢ Species

➢Males / females ➢Young / older individuals ➢Adaptations for diving

Sound production - larynx

Mysticetes have an unusual laryngeal sac: diverticulum -> resonator for sound production

Odontocetes have a beak like structure -> separated respiratory tract from mouth and oesophagus

Sound production - mysticetes

Skull is modified to accommodate palatal baleen plates as a feeding adaptation

-> Unusual Laryngeal Sac (Diverticulum) & Nasal Passages as Resonator

-> Auditory bullae of Mysticeti are wedged against the skull

-> bone and soft tissue conduction of low-frequency sound

-> Two blow holes

Sound production - dolphin (larynx)

Toothed whales: different than terrestrials – artenoid & eppiglottal cartilages elongated to beak-like structure, which separates respiratory tract from mouth / oesophagus – reduces risk of choking:

-> breath & swallow at same time!

-> Dolphins may produce sounds also in larynx for communication

-> But most Sound Production in nasal passages!

Sound production - odontocetes

➢The skull is shaped to accommodate a melon (or junk in sperm whales), facial muscles, the monkey lips/dorsal bursae (MLDB) complex, and nasal sacs for directional sound generation associated with echolocation and social interaction

➢Only one blow hole

➢The bullae are not fused to the skull but suspended in a spongy mucosa (peribullar plexus) by ligaments - no bone conduction

Sound production - dolphin nasal passage

1) Air is forced between a pair of MLDB - rapidly open and close (vibrate) -> produce sounds (clicks and whistles)

2) The phonic lips are two parallel ridges of transverse, keratinized tissue with fine grooves that direct flow into the vestibular air space for recycling (i.e., not expelled through the nares)

3) Airflow is under voluntarily control - variety of sounds is possible

4) The two MLDBs can function independently -> two different sounds simultaneously (= two voiced calls) Also clicks are produced independently from whistles

5) The melon contains lipids that are impedance-matched to seawater - sounds are produced by air moving past the vibrating monkey lips acoustically separated from melon, which focuses and directs sounds into water Higher frequencies are more focused than lower frequencies!

Sound production - spermwhales

Loudest sound in animal kingdom!

-> Junk homologous to melon

-> Spermaceti organ like right posterior dorsal bursa in other Odontoceti

-> Single pair of phonic lips located in right nasal passage beneath blowhole

-> produces high-intensity sonic clicks (400 Hz to 15 kHz and

up to 235 dB re 1 μPa at 1 m)

Clicks several paths in head:

Part of sound - out the front of the head, remainder travels backward through spermaceti organ to air sac adjacent to skull reflected back through the junk - focuses the beam out the front of the head!

-> Part of this sound beam is reflected a 2nd time by distal air sac at front of the head

-> it travels 2nd time to frontal air sac - reflected through junk - out the front of the head!

-> Inter click Interval – Head 1/3 of body length: calculate body size!

Hunting and prey detection, clicks 1–2s intervals

-increase in repetition-> whale approaches potential prey

-> At very close range, repetition rate so fast that individual clicks cannot be distinguished (buzzing), -> “creak”

Sound production - pinnipeds

➢vocalizations are sonic, diverse and vary by species, sex, age and season - social communication

➢In Air - often roars, growls, barks, snorts, whimpers, and whistles - exhaling through larynx, vocalizations -> pursed lips or nostrils

➢Underwater vocalizations - moving air between the lungs and pharynx, which causes membranes in trachea to vibrate without expelling air through the mouth or nostrils

Walrus

produces sounds with Lips (whistle/walrus), pharyngeal sac in their necks

Weddel seals

Produce sounds with Tracheal mechanisms, vocal folds

Bearded seals

Produce sounds with Vibration of dorsal tracheal membrane

Ribbon seals

Produce sounds with Air sacs on right side

Hooded seals

Have a inflatable nasal hood and septum (look like a balloon)

-> used for visual and acoustic display

Sound production - sirenians

Vocal folds in larynx -> variety of sonic vocalizations

➢Manatee calls (e.g., chirp-squeaks, squeals, and screams) 0.5-18 kHz, peak frequencies

1-8 kHz

-> Social communication and mother-calf recognition

-> Sounds are acoustically coupled to the water through fat pads in the neck

➢Dugong calls (chirp-squeaks, barks, and trills) frequency range of 2-18 kHz, peak

frequencies of 1-8 kHz

Sound production - sea otter and polar bears

Polar bear: laryngeal mechanisms of terrestrial mammals, lip vibrations - no underwater vocalisations

Sea otters - no underwater vocalisation

➢Aerial vocalizations short-range communication (e.g., screams, whistles, whines, hisses, snarls, coos, grunts, squeals, squeaks)

➢New-born pups routinely - high-frequency cry in distress or seeking attention

-> Adults produce high-intensity long distances (up to 1 km) screams, when distressed or female / pup separated

➢Territorial males produce high-intensity screams when interacting with females!

Echolocation

Auto communication:

➢Signals/sounds are sent out to create anreturning echo from obstacles

- echo is transformed in auditory cortex into map

– information about location, size & composition of environment / prey

➢Mostly high frequency clicks and sweeps

➢Animals explore and orient in dark environment

Echolocation - bottlenose dolphin

➢High frequency clicks (>100 kHz) broad-band (30-40 kHz), high peak (>220dB re 1μ Pa at 1m) short (50-80 μs) ➢Detection range 72 m, detection size 2.5cm

➢Brain is capable of very rapid auditory processing, integrating 0.25 ms interval inputs

➢Inter click interval (ICI) equals round trip & lag time: wait for echo to return & process before emitting new signal

➢Search (ICI) intervals slow and regularly - when closing in on target (ICI) intervals shorter - buzz

➢ICI = RT (round trip click - echo) + LT (lag time / processing time, targets 20-12m -> LT 19-45 ms)

Echolocation - special cases

➢Belugas ICI’s less than return time:process whole click trains in brain

➢Porpoises 5-10 x longer (150-600 μs) but half bandwidth (10-20 kHz), less loud (150-170 dB), very high frequencies (above 100 kHz), inner ears that are specialized for high frequency audition

Echolocation - mysticetes

Bowhead whales use echoes from calls to detect ice obstacle

Vocal repertoire driving factors

➢ Phylogeny, habitat; geographical separation; sexual selection; predator pressure

➢ Social complexity hypothesis of communication

-> group size, social networks and pair bonds in societies

➢ Context: e.g. food association calls: manipulation/arousal/information about food

Vocal repertoire factors in the sea

➢ Habitat: Favourable sound transmission in the sea versus air

-> Speed of sound 1500m/s (340m/s)

-> Transmission loss 60 times less, low light conditions

➢ Echolocation development in toothed whales

➢ Social whales: large & complex group structuresLarge repertories: Signature whistles bottlenose dolphins

-> Complex repertoires: Sperm whale codas

Humpback whale songs , Killer whales dialects

➢ Vocal tradition/culture

From calls to repertoires

➢Vocal classes - spectrogram: Clicks, Pulsed calls, Whistles, other calls distinguished by their frequency harmonics, sidebands, noisy parts etc.

➢Problems with naming - often arbitrary and anthropocentric

➢But vocalisations are context and situation dependent: coarse behavioural categories such as feeding,

socialising, travelling .. Give rough vocalisation patterns - fine scale behaviour needed but difficult to

observe underwater (drones and D-tags give new possibilities)

➢Long distance calls are loud, stereo typed, simple in structure, repetitive and temporally patterned

(rhythm, strong ordering) - low frequency calls of fin whales and blue whales suited to travel thousands of kilometres

➢Short range signals - acoustically more complex, encode information through subtle variations -

multimodal: information to receiver, distance, direction, identity, experience ...

➢Repetition or increased amplitude and frequency against noise

Acoustic structures

Syntactical rules in humpback whale songs

Individual differences in marine mammals vocalisation

➢Differences in vocal tracts lead to vocal differences "voice cues" but underwater high pressure changes vocal signals -> need for vocal control and vocal learning in marine mammals

➢Vocal learning is well documented for odontocetes, mysticetes and pinnipeds

➢But there also differences due to geographical separations, or sex and age related

Vocal repertoires - odontocetes

Produce species-specific, frequency-modulated sonic and ultrasonic sounds such as "whistles" (1-120 kHz), pulsed sounds "calls" (1-60 kHz) and clicks (10-300 kHz) for communication and echolocation

Odontocetes - whistles

➢A) Tonal whistles: variable structures all dolphins

➢B) Stereo-typed whistles: re-occurring stable structure

Bottlenose dolphins, all dolphins

➢C) Ultrasonic Whistles: main energy 20-60 kHz (> 90 kHz) Killer whales and Long-finned pilot whales

Stereo-typed pulsed calls

➢A) Tonal calls, simple to complex calls

➢B) Combination of calls

➢C) Two-voiced calls

➢D) Distinct calls (e.g. signature whistles, dialects)

Pulsed calls

➢Variations of calls - graded information may carry information on emotional state, alertness, excitement, hierarchy, danger, food..

➢Other calls without distinct structures such as buzzes, grunts, squeaks....

Combination of calls and other utterances

Calls are often comprised as patterned combinations (Weddel seals, Humpback whale songs, Pilot whales..) & often combined with other displays (e.g. hooded seals, jaw clapping dolphins..)

Clicks

➢Main vocalisation- echolocation- but also communication

-> Buzzes - e.g. killer whales - help to heard herring?- part of calls

➢Not well studied

Spermwhale - vocal repertoires

Click communication

-> echolocation clicks

-> clusters of 3-20 clicks called codas - social communication, reflect dialects of female groups

-> Large males make a "slow click" or "clang" to announce themselves to female groups

Vocal repertoires - context

Sperm whale codas - context-sensitive and combinatorial vocalization

- clans have their own set of codasKiller whale group dialects:

-> In Canada, each group has its own call type set, related groups share Call Types

-> avoid inbreeding

Pilot whale group dialects: first results show group specific call types but under investigation

Communication - dolphin groups

Recognition of the individual Signature whistles SW: Bottlenose dolphin signature whistles:

-> New-born learn mothers SW, within 3 months develop their own SW

– announce themselves

– addressed by others

– used in absence of the owner of the SW

Communication - behavioral context

➢Norwegian killer whales: salmon feeding & carousel feeding

➢Icelandic carousel feeding KW similar to Norwegian KW

-> Communicate during hunting and feeding

Mother calf communication

➢Contact calls

➢Distress calls

➢Mother contact call for calves in long-finned pilot whales

Male-male competition - territories

➢Aggressive calls

➢Distress calls

➢Often accompanied with aerial displays such as clapping, inflated hoods, jaw claps etc

Vocal repertoires - mysticetes

They produce a variety of amplitude-and frequency-modulated calls -moans, growls, or simple songs frequency range 7 Hz in the blue whale to 24 kHz in humpback whale songs

Communication – long-distance

Sounds that have wavelength longer than the whale and may be used for long-distance (thousands of km) communication:Fin whale & Blue whale low frequency calls >1000kmSignals are loud, stereotyped, spectrally simple, long, repetitive, and temporally patterned = shaped by sexual selection (complex)

Noise pollution

Most marine mammals only visible 1-10% at surface = acoustic monitoring useful tool to estimate distribution and abundance!

-> Man made noise can interfere and become a problem for marine mammals (e.g. Richardson et al, 1995) Past 50 years noise in Ocean 20 X increase!