Is there an insecticide to kill flies, which is safe for wildbirds

Hi  bird friends-

I have recently put down a  ground feeder for the  mourning doves that
visit my patio--and I am inundated with flies.  I put up a couple of
non-toxic flypaper strips, but those  pesky flies stick to the
groundfeeder mostly so the flypaper doesn't work.  A few of the
smaller birds, house wrens mostly , also feed from the groundfeeder.
Is there any safe way to get rid of the flies --maybe there is a
product they can't stand the smell of which wouldn't bother birds.

Your advice will be greatly appreciated.

TIA
 --
  deet