>Hmm, very interesting. I have two hyoptheses:
>
>1.) Since Don beat me to the keyboard, I would venture a guess at the
>Baccus theory. That is, they do nest in close quarters and if the road
>were near a bank they were nesting in, it's feasible that cars could be
>killing them left and right as the birds fly in and out of nesting holes.
>
>2.) Aerial insecticide use after Hurricane Hugo caused brief but
>widespread Tree Swallow mortality in coastal South Carolina. It could be
>that crop-dusting may have somehow caused this, if their prey (or perhaps
>the birds themselves) were sprayed with insecticide and promptly consumed.
>
>-------------
>Michael R. Smith

I'll add a third hypothesis, which is the "swallows on the road" one. Many
many times I've seen masses of swallows settle on a road, and in most of
the cases, I couldn't really figure out why. I've also seen substantial
mortality at these sites, although usually no more than a dozen or so
birds. Swallows are very gregarious, so they might tend to settle en
masse. I think the nesting-colony hypothesis doesn't make sense, as that
would cause mortality all through the nesting season, not the massive death
that Dave observed, which I suspect was at a staging area.

Dennis Paulson, Director phone 206-756-3798
Slater Museum of Natural History fax 206-756-3352
University of Puget Sound e-mail dpaulson at ups.edu
Tacoma, WA 98416