Chris Hill wrote:

"I doubt if the usual TV tower data would really help, at least if the
data is collected daily, as I think it is."

At the big TV tower near Tallahassee, Florida, one of the nation's most
profligate bird killers, people recorded exactly where each bird was picked
up, and I was thinking there might have been a clumping of birds if a flock
went through. There were an awful lot of guy wires for the birds to hit,
but I suppose the vast majority (hopefully) passed through the maze of
wires without mishap. The sample size was large; thousands of birds in
some seasons.

"To me, passerines migrating in flocks seems quite plausible - why should
it really be harder for them than for geese (and yes, geese do migrate at
night)? In particular, I find the reports of calling nocturnal migrants
suggestive. On Long Island (coastal New York), one can count Swainson's
and Hermit thrushes in the hundreds passing over if you know the call
notes, as they call while flying. Why would they call if not to keep
flocks together?"

But Swainson's and Hermit thrushes *don't* flock during the day, so that's
even more amazing. When I lived in Florida, I kept careful track of those
nocturnal chip calls, and I never felt there was any clustering of any one
kind of passerine in such a way to imply a flock. Yes, the sky sometimes
was full of them, but it sounded like individual chips floating down out of
the darkness (let the chips fall where they may.....).

And, finally, this makes me recall that I spent dozens and dozens of hours
watching migrants cross between me and the moon (part of a big project that
went on for several years studying migration by this technique), and I
*never* saw a compact flock of passerines (it would have been obvious).
There could have been very loose flocks, but I might have expected several
birds to pass in quick succession in that case, and that didn't happen. I
should have recalled this when I first opened this subject. Yellow-rumped
Warblers were primarily winter visitors, not migrants, in Miami.

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