On Fri, May 01, 2009 at 03:00:27PM +1000, Stephen Ambrose wrote:
> I've heard four anecdotal explanations for the movement of pelicans to
> inland waters to breed, although I've not seen any of them scientifically
> investigated, i.e. that pelicans are able to:
> 1. detect changes in the atmospheric pressure associated with heavy rain;
> 2. smell the floodwaters from afar;
> 3. hear the sound of distant thunder associated with heavy rain, especially
> ultrasonic frequencies
> 4. Individual pelicans disperse over long distances on wind currents and
> when one detects inland floodwaters (either accidentally or intentionally),
> it flies back to the coast and communicates its knowledge to others.
Its a fascinating topic and I don't think any of these explanations
are plausible - but I can't conceive a plausible explanation either.
For #3 has a common confusion - ultrasonic sound is above human hearing in
frequency -e.g. (most) bat echolocation calls. Ultrasound propagates
poorly because absorption of sound by air is proportion to frequency.
Generally you talking tens of metres or less for detecting ultrasounds.
Infrasound is below the human hearing range - e.g some elephant and
cassowary calls. It propagates very well and infrasounds can certainly
be heard over tens of kilometres. So its conceivable a pelican could
hear a thunderstorm as much as 100km away but it still seems inadequate
to detect Lake Eyre filling from the coast.
Having GPS trackers on a pile of pelican when Lake Eyre filled
would be fascinating.
Andrew
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