Bryan Gates wrote:

Interesting thought, Dennis. Does anyone know of literature on why warblers
in general do not migrate as flocks?...or why YRWAs are (or are not)
different in this regard? Then again, who knows what happens at night?
Perhaps those radar blips are pure flocks of MacGillivray's, or Yellows,
or...? Those with exceptional ears and who pretent to sleep under the stars,
tend to claim that they hear groups of mixed species passing over.

The thing is, I don't think it has been suggested that nocturnal passerines
ever migrate in cohesive flocks, which is why I raised the point with the
YRWAs. Most flocking birds migrate by day, although both waterfowl and
shorebirds fly by night as well. How do any of them manage it? WIth lots
of pushing, shoving, and cursing ("stay in your own lane")? Or do they
fly only on nights when they can see each other? All those chip calls of
passerines may serve to keep them in touch with one another, but for what
reason?

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