My dissertation was on the topic of bottlenose dolphin sound production during biosonar. One of the things that I’ll be reporting on is a figure for the minimum intranarial pressure seen at the time of click emission in dolphins. Well, yes, it is in my dissertation, available online, but it isn’t really official until it is out in the technical literature.
What I want to talk about here and now, though, are the approaches to this number seen in past research.
The first stop is a paper by Evans and Prescott, published in 1962. Bill Evans, I will note, was also my dissertation advisor.
Evans, W. and Prescott, J. (1962). “Observations of the sound production capabilities of the bottlenose porpoise: A study of whistles and clicks”. Zoologica 47, 121–128.
This paper provides an answer to the question, “What can you do with a dead dolphin head?” One thing to do is to insert a tube hooked up to pressurized air and run that through the nasal passages. What they reported was that they heard click-like sounds produced when the pressure delivered into the head was 1.5 PSI and the flow rate was ten liters per minute. Converting the first figure gives 10.3 kPa pressure, about one-tenth of an atmosphere of pressure. If a click train lasted three seconds, the second figure means that about a half a liter of gas would pass through the nasal passages and up into the vestibular sacs during that time. I suspect that is on the high side of things, but probably reasonable considering that they were looking at a dead specimen. Another aspect to consider is that live dolphins can often produce clicks with negligible energy in the frequency range covered by human hearing. Being able to hear click-like sounds indicates that the system may not be operating in its best range post-mortem, also not terribly surprising.
The next stop will be Amundin and Andersen 1983.