Every fall, about the first week of September, an incredible sight takes place right over Bow Narrows Camp on Red Lake, Ontario.
The sky above the southern half of camp is filled with gulls, seemingly both herring and ring-billed gulls. They twist and turn, silently, flying back and forth, about tree-top level but right over our lawn on the edge of the lake.
It took me years to figure out what they were doing. They are catching small, blue flies that only appear at this time. These flies are almost invisible from the ground, are poor fliers and basically just hover. Whatever they are, the gulls are bonkers for them. I've never seen gulls go for insects on the wing other than this.
The flies must be exceptionally nutritious. The gulls always forsake eating fish guts when the flies are out. Incredibly, there will be no gulls on our fish gut rock -- the rocky island where we dump the innards each day. We will drive our boat carrying the fish gut pails right beneath the bug-catching gulls and none of the birds will follow us.
As soon as the flies are gone, so are the gulls, at least, it would seem, the resident gulls.
They seem to eat the flies as a way of stocking-up on energy for migration.
For the rest of the fall there are but few gulls at the fish gut rock and these seem to be newcomers. They don't, for instance, seem to recognize what our boat is doing as it heads toward the rock. In the summer the boat is swarmed by the resident gulls.
If anybody has any information about the identity of the flies, I would appreciate your telling me.
I can't find any mention of such behaviour in my bird books or on-line. Please send me an e-mail at fish@bownarrows.com or leave a comment on the blog.
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