Michael Price wrote -

>But Interior migration routes would differ from coastal routes, and I'm sure
>it gets more complicated when birds from the Interior move out to the coast,
>which they may do at several or many locations. I *do* know from asking
>people in the Fraser Valley to keep track of spring arrival dates that
>arrivals on the inner coast here in Vancouver BC consistently are about a
>week to two weeks earlier than even 50 km inland, and it seems to be the
>same southbound, though the data's much sparser. The same discrepancy
>obtains between Vancouver & Victoria BC, and I imagine that were arrival
>dates in either direction monitored on the actual outer coast of BC, say in
>Tofino, that they'd be even earlier. It's clear from Vancouver & Victoria BC
>migrational data that birds migrate along the outer coast earlier than they
>do the inner coast, and earlier along the Inner Coast than inland, with
>about a week between each.

Yes, and probably the first arriving birds are adults. The fact that
outer coastal birds arrive first suggests a more northerly origin with
Alaska being the most likely place.

>But, old weather guy, wouldn't many shorebirds from Alaskan populations be
>able to stage at some location on the south or southwestern coast as they do
>on your PG lakeshore, wait for a Pacific Low to come sweeping by, then
>ride on the northwesterlies which come in behind the cold front, and
>hitchhike down on those tailwinds? Landfall then becomes a matter of where
>the jet stream pushes/pulls the Low to intersect the Coast.

Plausible. Note that the yellowlegs passage through the Okanagan
Valley is minor compared to the coastal one. However, this could just
be a simple overflight of relatively hostile habitat.

>What I'm trying to figure out is why shorebirds sometimes appear more or
>less simultaneously along the Pacific Coast from Cascadia to California (I
>say, that has a nice ring to it, doesn't it? "From Cascadia to California",
>like the title of a National Geographic article of the 1950's), and it seems
>that two possibilities are, first, that a big bunch set out from the north,
>some drop out sequentially at various sites along the coast and the
>strongest keep flying until they reach Al's region or further in a day or
>two of sustained flight or, second, that they again leave en masse after
>staging but use assisting winds associated with Pacific weather systems,
>coming ashore wherever these systems do.

I'm afraid that we will never know the answer to this question until
we either get a lot of useful satellite data from radio-tagged birds
or a better network of banding sites in Cascadia. I prefer the
scenario which imparts a southeasterly trend to the total migration.
Thus most of the coastal birds would be Alaskan birds while most of
the interior birds would never reach the coast. Can't wait until we
see some actual data to either confirm or deny this.

,Jack





Jack Bowling
Prince George, BC
CANADA
jcbowling at mindlink.bc.ca