On Fri, 30 Sept 1994, Gene Hunn wrote:

There does appear to be an overflight pattern with Red Knots in spring.
They are apparently quite scarce north and south of the southern
Washington coast but thousands pass through Willapa Bay and Grays Harbor
in late April and early May, fatten here, then perhaps fly non-stop to
breeding areas in the arctic. However, I feel sure that the accidents of
social geography account for the vast majority of the difference in
numbers & variety of rare shorebird sightings on the west coast. Iona,
Reifel, and Boundary Bay are virtually on the doorstep of a metropolitan
area with well over a million people. Seattle has about the same number
of people but we have NO shorebird habitat within an hour's drive and
precious little within two hours. Some of Washington's best shorebirding
areas are closer to Portland than to Seattle. An avid shorebirder who
confined him or herself to within a radius of 25 miles of Seattle might
be lucky to see a grand total of 100 shorebirds of all species in a
year! We don't have a chance!

Gene.

On Fri, 30 Sep 1994, David B. Wright wrote:

> On Fri, 30 Sep 1994, Greg Gillson wrote:
> > Would the pattern of more rare shorebirds in California have anything to
> > do with the latitude that the birds normally fly to?
> >
> > In other words, are the birds wintering in the right place (latitude), but
> > wrong side of the Pacific?
> >
> > If the birds are wintering in California, but only migrating through
> > B.C., Washington, and Oregon, then that would explain the higher numbers
> > discovered in California.
> >
> > --
> > Greg Gillson <gregg at tdd.hbo.nec.com>
> > Hillsboro, OR
> >
> That is a plausible explanation, but as Mike Patterson pointed out, you
> really have to be able to rule out sampling bias to be sure that the
> apparent pattern (more stray Eurasian shorebirds landing in CA than in
> PNW) is even real. It seems equally plausible that denser sampling of
> shorebird habitats during migration could account for the difference, and
> the proximity of big population centers to good shorebird spots in CA
> leads to dense sampling. Someone please correct me if I'm wrong, but I
> have the impression that Iona in BC reports more rare shorebirds than
> single good shorebird localities in WA and OR. If this is true, then it
> supports the sampling bias hypothesis better than the overflight hypothesis,
> as Iona is close to a big pop. center allowing many birders daily access
> (cf. CA). (Unless you want to argue that the birds are stopping in Iona
> before moving on, which is getting pretty ad hoc). Even if I am wrong about
> Iona, it seems obvious that sampling in CA is on average signicantly
> denser than in PNW.
>
> An immediate test of the relative merits of the 2 explanations would be
> to plot competent-observer hours per unit of area for localities in PNW
> and CA vs. number of rare birds found there. The sampling bias
> hypothesis would predict a high positive correlation between the 2
> variables, independent of location (e.g., poorly sampled localities in CA
> would fall out with localities having a similar level of sampling in PNW).
>
> This is not to argue that the overflight hypothesis is necessarily wrong,
> just that it is premature to invoke it as the best explanation without
> ruling out sampling bias first.
>
> David Wright
> dwright at u.washington.edu
>
>
>