Caren,

I live about 4-5 miles NNW of the huge crow roost on Foster's Island,
near the UW, and large numbers of crows from that roost fly over my
house morning and evening, especially in winter. I often drive down one
of the streets between here and there at the appropriate times, and I
see this river of crows is really quite narrow, and it always seems
that way coming over my house. There are, of course, multiple rivers
going in all directions from the roosts, but each river seems to me to
be quite discrete. I see another one flying from that roost directly
west on 520 in the morning, the sky filled with crows over me as soon
as I turn west from 25th Ave. As soon as I turn south on I-5, that's
the end of them. I see another flight over the Puyallup River Bridge in
Tacoma that seems equally narrow. I have the impression that thousands
of birds use some of these "rivers." There are a lot of crow studies
coming out of John Marzluff's group at the UW, and perhaps they can
enlighten us on whether individual crows always stay in their own
river. Crows are without a doubt some of the most interesting birds
around; I only wish I understood half of what they do!

Dennis
-----
Dennis Paulson
1724 NE 98 St.
Seattle, WA 98115
206-528-1382