Acoustics forelæsning week 2 Flashcards
Intended learning outcomes
Describe the basic physic principles of sound production, transmission and reception in marine mammals, inc. ways to measure it.
Describe the anatomy of sound production and reception in pinnipeds and cetaceans
Describe the various uses of sound for foraging, navigation and communication
What is sound?
Sound is propagating pressure waves that push and pull layers of air, water or some other medium
Sound cannot exist if it does not have something to travel through, so no sound in a vacuum or in space
Benefits of sound in water:
- High speed of sound (1500 m/s vs. 330 m/s)
- low transmission loss
Amplitude and frequency
The compression and expansion of air/water layers result in a certain amplitude (A) and wavelength (λ)
Frequency (hertz) is number of wavelenghts per second
Wavelength and frequency
- Trade-off between communication distance and information
- Long wavelength = low frequency = far distance but limited info
- Short wavelength = high freq. = short distance but much info
Frequency and body size
- Hearing frequency range depends on body size and the anatomy of sound producing/receiving organs
– Blue whale (33m): long wavelengths = low freq (10-150 Hz)
– Hectors dolphin (1m): short wavelengths = high freq (130 kHz)
Amplitude and intensity (volume)
- The larger the amplitude the louder the sound
- Intensity measured as relative unit in decibels (dB)
- 10 dB increase = 10 times increase in intensity (power)
Intensity of sound (volume)
- Acoustic intensity (I) is the average amount of energy or power passing through a unit area (Watt per m2)
- 10x distance = 100x lower intensity = transmission loss
- Toothed whales focus the sound to minimize loss
Acoustic monitoring (eavesdropping)
Passive acoustic monitoring (PAM); using hydrophones to detect animal sounds, including marine mammals
A spectrogram provides graphic representation of sound intensity (colours), frequency (y-axis) and duration (x-axis)
Pro: Can be used for species identification, has a long detection range and low disturbance
Con: Cannot detect silent animals, and best quality when recorded “on axis” (in front of the animal)
Acoustic monitoring (eavesdropping)
Passive acoustic monitoring (PAM); using hydrophones to detect animal sounds, including marine mammals
A spectrogram provides graphic representation of sound intensity (colours), frequency (y-axis) and duration (x-axis)
Pro: Can be used for species identification, has a long detection range and low disturbance
Con: Cannot detect silent animals, and best quality when recorded “on axis” (in front of the animal)
Sound production in pinnipeds
- All pinnipeds produce sound in the larynx, like terrestrial relatives
- In addition…
– Walruses make sound by clacking with teeth, inflated pouches in throat, whistles, etc (https://www.youtube.com/watch?v=OAVL61yeCYs)
– Grey seals clapping with front flippers (https://www.youtube.com/watch?v=69n8jnFTmBg)
– Hooded seals have inflated hood and nasal sac
Sound reception in pinnipeds
- Pinniped hearing like terr. relatives, except for:
– Larger tympanic bulla and enlarged middle ear bones => better low-freq hearing in air
– Cavernous tissue in outer and middle ear => better high- frequency hearing underwater
– Muscular control of ear opening in phocids/walrus - Otarids hear at higher freq than phocids/walrus
Sound production in odontocetes
- All toothed whales produce echolocation “clicks” to orientate, detect and capture prey
- Several factors affect the detection range:
– Source level (SL); depends on size of animal + melon
– Transmission loss (TL); distance, noise and source
– Reverberation level (RL); noise and reflections
– Target source level (TSL); depends on size of target
– Echo level (EL)
Skull asymmetry
- Skull asymmetry correlate with sound intensity measured as source level (Log10 dB)
- More asymmetric species capable of emitting louder sounds, providing a longer detection range of prey…
- Skull asymmetry in toothed whales varies by species
- Highest in monodontids and globicephalins
Sound reception in odontocetes
- Ear canal is very narrow (plugged in mysticetes)
- Jaw 6x more sensitive to sound than ear canal
- An alternative sound reception pathway!
– Pan bones on mandible
– Fat channels
– Tympano-periotic complex (very dense bone)
– Emerged in mucus, oil and air within sinuses and thus more or less isolated from the skull
– Tympanic membrane is calcified (hard bone)
Sound production in mysticetes
- Not sure how baleen whales make sound
- No phonic lips; a larynx, but no vocal cords…
- Perhaps sound produced by laryngeal sac?
