On Sun, Mar 07, 2004 at 08:16:20PM +1000, Bob Forsyth wrote:
> Could it be that Eagles, Kites and Corvids feeding on carrion on the
> road get their first warning of an arriving vehicle by road vibrations?
Vehicles do produce substrate-borne vibrations including I assume ground
surface waves. Ground surface waves may propagate significantly further
than air-borne sound waves but they propagate slower than sound waves -
at least this the case in studies of elephants, it varies with substrate.
Vehicles also produce a lot of air-borne sound at low frequencies which
propagate well in most environments and are heard well by birds.
They may be able to hear a vehicle at distance of 1+ km.
It seem unlikely to me that the feet of corvids and raptors could
detect the surface waves from a vehicle at these sort of distances.
but an Elephant maybe could.
> I use a pair of $20 warning devices But they emit an audible whistle
> when the vehicle is going fast enough. They work by air being forced
> through a venturi, much like an umpires whistle. Kangaroos, feeding on
> the side of the road sometimes will look up & freeze.
> But those off the road bound off in all directions, including across
> the road.
I'm sceptical even about this. If the whistle is audible to a human,
the kangaroo might be able to hear it but have you tried standing next to
the road and seeing how close the vehicle is before you hear the whistle?
Even if the kangaroo can hear the whistle above the vehicle sound, its not
obvious why a would produce a different response to the vehicle sound.
I'd take some convincing.
Habituation is a major problem with "scarers" and can defeat much
more well-founded appproaches, e.g. playback of predator calls in
orchards but I doubt these devices even reach that stage.
Andrew Taylor
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