dpb wrote:
The Daring Dufas wrote:
...

If you knew what species the birds were, you might be able to find a
recording of their warning cry or the cry of a predator bird to play
at regular intervals which might scare them off.

Indeed...many (I think all that showed up in my search for the previous
paper abstract that I had seen some years ago) of the ultrasonic
products also have such soundtracks w/ them so testimonials to the
effectiveness of the ultrasonic devices probably have absolutely nothing
to do w/ the ultrasound component do anything except adding to the
marketing hype...

I'm not sure how effective such are, either, long term. And, of course,
there's the nuisance factor of the cure as well as the actual problem in
that route.

Starlings, for example, are terribly persistent about roosting--scare
them up at eventide and they'll simply circle and return unless are
extremely persistent and often even then a large number will eventually
just ignore noise, movement, etc., once dark sets in.

--

You could always strap a concrete vibrator to the tree and put it
on a timer. Rattle their little beaks every now and then.

TDD