I mentioned this thread to Tony Howard, who is the person who does half the
voice sections for HANZAB. He has just recently done the Nightjars for the
next volume (which is comign out next August BTW), and says that nothing in
the literature mentions ultrasonic calls produced by nightjars, either in
Australia or OS (the North American Nighthawks voices have been very well
studied and if they were any ultrasonic component he thinks it woudl have
been picked up). He also mentioned that the hypothesis that what is being
recorded is the harmonics of audible calls.
We also discussed why Nightjars would need ultrasonic calls. Oilbirds (from
S. America, nightjar relatives) and our own White-rumped SWift use them, but
they nest in pitch-dark caves and need echo-location to find their nests.
This would not apply to ground nesting Nightjars, who would also seem quite
capable of catching insects without the use of echo-location.
Which is not to knock the observation on the head, I hope, but just to add
some cautionary thoughts.
I guess sonagrams are required before anything else.
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Dr John Leonard
PO Box 243, Woden,
ACT 2606, AUSTRALIA
'... after only twenty years in existence much of the
environmental movement has taken on the form of just
another corporation or interest group. Their interest may
be disinterest, but their methods are one with the rational
élites and are therefore limited to the details of corporate life.
[They] ... are attempting to justify restraint and a common-
sense approach to self-respect with the use of intellectual
tools designed to eliminate both.' John Ralston Saul
http://spirit.net.au/~jleonard
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