To the previous 3 hypotheses, I'll add a fourth, or perhaps a
corrollary (Hmm, don't know if I have the right number of r's and l's in
that word):

The pattern of birds on the road and not the shoulder might be due
to scavenger preference for birds on the shoulder. Ravens and crows
are likely smart enough (or face 'hard selection' pressure) to learn
that the shoulder is a safer place to snack on road kill than the
road. Ground-based scavengers lurking in the vegetation next to the
road would get the shoulder birds first.

Of course, if this hypothesis is correct, then mortality itself could have
been due to almost anything that would cause mass die near a road.

Kelly Cassidy

> >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