Folks,
I'm reading Bernt Heinrich's first book on ravens (the title escapes me). It's a fascinating study of animal behavior. It's also a great example of the scientific method. He started out with some assumptions almost all of which were proven wrong. He gathered data through a bunch of elegant experiments and tied together behaviors that at first seemed completely unrelated. And on top of all this, it's a very well written book.

Anyway, he baited ravens with piles of meat and suet scraps. He also baited jays and a shrike with flies. It was too early in the season for swallows, but I think the methos would work. In mid winter, he heated the cabin where he worked with a wood stove. The heat awoke the cluster flies that flew out the door in flocks every time he opened it. The jays were feeding at one of his meat piles and switched to flies. The shrike just happened by and stayed for a few rounds of flies. He didn't leash them, somthing that might be easier with cluster flies than with gnats.

John Fleckenstein, zoologist
Natural Heritage Program
Forest Resources Division
EMail: John.Fleckenstein at wadnr.gov
Phone: 360-902-1674