Acoustics and Communication Flashcards
What are some modes of communication?
- Chemical
- Electrical
- Tactile
- Visual
- Acoustic
What are some reasons why marine mammals produce and recieve sound?
- Echolocation and passive listening
- Communication and social interaction
Define communication
The sharing of information between individual animals
What are the two steps involved in communication?
- Communication signal produced by a sender
- The signal is transmitted to and imparts information to a receiver
Describe sound production in odontocetes
- Echolocation clicks: produced by the MLDB
- Whistles: produced by the larynx
Describe sound production in Mysticetes
Low frequency pulses: produced by the larynx
Describe sound production in Pinnipeds
- Produce sounds in air and underwater
- Sounds are produced in the larynx
Describe sound production in Sirenians
Sounds are produced in the larynx
What are the costs and benefits of communication?
- Neutral: benefit to both the sender and receiver
- Manipulation: benefit to the sender at the cost of the receiver (ex: deception)
- Eavesdropping: benefit to the receiver at the cost of the sender (ex: interception of the signal by a predator)
Describe Humpback Whale song
- Complex series of repeating units, phrases and themes
- Frequencies = within human range
- Can last up to 20 minutes
- Change dramatically over time
Old themes are not reused
Do Humpback Whale songs convey complex information?
- No!
- All whales located in the same vicinity sing similar songs
- This is the equivalent of people gathered in a room saying the exact same word or phrase (no important information is conveyed)
What are Humpback Whale songs used for if they do not convey complex information?
- Reproductive advertisement
- Songs are primarily produced by males
- Produced mostly on breeding grounds (to attract females)
- Correlation with male-male interactions
- Changes over time are matched by all males (ex: if a new male enters a breeding population with a new song, the other males in the breeding population will adopt the same song (why))
Describe Fin whale sounds
- Low frequency
- Can travel long distances (theoretically)
- SOFAR channel
What is the SOFAR channel
- The ocean consists of different layers (due to salinity and temperature)
- Sound emitted at a certain depth bounces between these various layers and can travel for hundreds of miles
- The speed of sound reaches a minimum velocity at around 600-1200 meters (this layer = SOFAR channel). In this layer the effects of temperature, water salinity, and pressure combine to produce the best conditions for sound transmission.
- Sound waves naturally bend towards layers of lower sound velocity (stay within the SOFAR channel)
- Loud low frequency noises made at this depth can theoretically be detected for thousands of kilometers (because they bend in the SOFAR channel)
Do Fin Whale sounds convey important information?
- No!
- Sounds traveling over immense distances are unlikely to be of biological importance
- Sounds are likely used in reproduction
Describe Killer Whales social cliques
- Killer whales live in the most stable groups documented for any ANY mammals
- Different groups = distinguished by the communication sounds they produce
- Each pod has its own specific dialect
- Pods with related dialects belong to a clan
- Different clans have no dialect features in common
- Group specific vocalizations function in group recognition
What do the different dialects in killer whales suggest about their relationships?
The differences in dialects between killer whale pods directly relates to the genetic relatedness between pods and species
Describe Sperm Whale sounds
- Rhythmic vocal patterns (“codas”)
- Some appear to be individually specific
- Some appear to be group specific (shared “codas”)
How are Sperm Whale sounds observed?
Examining the differences in timing between individual clicks
What term is used to characterize Bottlenose Dolphin societies?
Fission-fusion societies
Multiple groups come together then break off repeatedly
Describe the role that John C. Lilly had in characterizing dolphin communication
- Early research looked for content specific vocalization
- No supporting evidence was found
- Study was hindered by not knowing which individual dolphin in a group was making the sound
- Majority of research was conducted on captive dolphins
- Captive dolphins imitate trainers instead of producing natural sounds
Overall, Lilly’s studies led to misconceptions around dolphin communication
What were David and Melba Cadwell’s contributions to characterizing dolphin communication?
- Recorded isolated captive dolphins
- Found that each dolphin produced a distinctive signature whistle (important for identification)
Describe the individual calls of Bottlenose Dolphins
- Stereo-typed
- Repeated frequently
- Stable over time (individuals have signature whistles their entire lives)
Describe referential communication and how dolphins utilize this form of communication
- Individual identity information is encoded independent of the signalers voice or location in the natural communication system
- Ex: a dog knows their name (“max”) rather than the way that you pronounce the name
- Dolphins understand the information being conveyed in signal rather than just the sound of the signal being produced
What is anthropogenic sound and what are some ways in which in which it is produced?
- Anthropogenic sound is human-made sound
- Examples are:
- Drilling
- Shipping
- Naval sonar
- Seismic surveys
Why is anthropogenic sound an important threat to marine mammal populations today?
- Being able to effectively transmit and receive sounds is key for foraging, migration and reproduction in cetaceans
- Anthropogenic sounds interfere with this
Does source level (source of anthropogenic noise) always = received level (level at which marine mammal hears sound)?
- No!
Whether or not a sound can be heard depends on: - Spreading
- Absorption: high frequency sounds are absorbed faster than low frequency sounds
- Presence of background noise
- Where the source and receiver are in the water column
What are the three effects of anthropogenic sound?
- Auditory effects
- Other physiological effects
- Behavioral effects
Describe the auditory effects of anthropogenic sound
- Temporary and permanent threshold shifts (TTS and PTS): hearing loss
- Masking: too much background noise masks or covers sounds of interest
Describe the other physiological effects of anthropogenic sound
- Mortality
- Tissue damage: decompression sickness (from surfacing too quickly), blast trauma etc.
Describe the behavioral effects of anthropogenic sound
- Stranding after panic or trauma
- Changes in dive behavior: increases / decreases in the frequency of dives
- Habitat abandonment: temporary or permanent
- Modification of acoustic signaling: signaling less frequently
Temporary Threshold Shifts (TTS)
A reduction in hearing that is fully recoverable. Depends on noise..
- Frequency
- Level
- Duration
- Previous exposure
Directly studied in marine mammals
Permanent Threshold Shift (PTS)
- Not recoverable, related to some of the same factors as TTS
- Could be related to repeated TTS
Not directly studied in marine mammals
What are some effects of masking?
Increased masking noise can reduce effective communication ranges
*Ex: a whale’s listening space is reduced by vessel noise making it harder to detect prey
What other parameters other than sound level determine the effects of noise on marine animals?
- Sound frequency
- Exposure level
- Duration
- Source range from an animal (sound attenuation)
- Individual hearing ability and exposure history
- Individual age and sex
Describe the zones of sound influence
Marine mammals within the zones closest to the source of the noise are likely to experience the greatest damage (PTS, TTS). Marine mammals farther from the source of the noise are likely to experience less damage (masking, behavioral changes) .
