Echolocation in Cetaceans Flashcards
(18 cards)
What is the purpose of echolocation of cetaceans?
- Cope with vision difficulties underwater as light is poorly transmitted in water
- Suspended materials (soil particles/plankton) have limited visibility
What type of cetacean are known to use echolocation?
Odontocetes (toothed whales & dolphins)
What type of cetacean are not known to use echolocation?
Mysticetes (baleen whales)
What are sounds both Odontocetes and Mysticetes create for communication?
squealing, creaking, wailing noises
How do ‘hydrophones’ in each ear help localise sound sources in mammals?
By discriminating between the times the sound is received by each ear
The pressure of sound exerts on bones causing vibration in the skull
What is a disadvantage of mammals with this type of skull submerged in water?
Unable to localise sound source accurately
What features of cetacean retain constant sound-reflecting & sound-insulating qualities through different pressures in water?
Bullae are insulated by air sinuses which extend forward into the pterygoid fossae
Each sinus is connected by a eustachian tube to the cavity with an oil-mucous emulsion, foamed with air, and surrounded by fibrous tissues
How is the tympanic bullae different in cetaceans compared to other mammals?
Tympanic bullae are not fused with the skull, and in specialised dolphins & porpoises, bullae are separated with a gap between the skull
Which part of a dolphin’s head is most acoustically sensitive?
thinnest part of the lower jaw
What is the pattern of echolocation in Tursiops?
train of ultrasonic clicks (audible to humans but cover a wide spectrum of frequencies)
Give examples of how rates vary amongst odontocetes?
Orcinus orca: slow repetition rate of 6-18 clicks/s
Inia geoffrensis: 30-80 clicks/s
Where do cetacean clicks/buzzes originate from?
Produced by vibrations of the nasal plugs - these plugs are muscular valves at the blowhole that close the nares
How is the sperm whale (Physeter catodon) unique in terms of echolocation?
Uses a unique mode of foraging called echo ranging
How long does 1 sperm whale click last and how many separate pulses does it contain?
Click of sperm whales consist of a series of pulses, which lasts for 24 milliseconds & composed of up to 9 pulses
Knowing that sperm whales feed on squid that takes in depths, how do they use forage successfully?
Echo scanning to locate food under conditions that require long-range echolocation (deep sea)
How do blind river dolphins (Plantanista gangetica) swim?
On its side with the ventralmost flipper either touching the bottom or moving within 2-3 cm
Why do blind river dolphins have reduced eyesight?
Absent lens, only contain retina can detect light
What are the features of echolocation in blind river dolphins?
Produces a series of pulses at a rate of 20-50/s, ranging between 15-60 kilohertz
Can direct their pulses into a narrow beam
