An interesting idea. Makes me wonder several things, how far does any
particular bird travel in a day or two? Obviously this would be affected
annually by local weather but assuming a bird flies 120 miles a day for two
days, then stops and feeds, this would equate to perhaps similar distances
between sightings as you suggest. There could also be very specific
migration corridors, formed by specific habitat opportunities, so particular
places might be skipped by the earliest migrants. Or, there may be an
actual genetic pattern to earliest migration, something within the genes
which makes say, 10% of the birds move out earlier than the 90%, so what we
are seeing is the 10%, the high risk takers. I would imagine there could be
reproductive rewards for the risk of being the earliest much like there is
in plants like Salmonberry, who put out less than 5% of their blooms during
times where a hard freeze is still a high possibility.

The world is full of interesting questions,

Rob Sandelin
Naturalist, Writer

-----Original Message-----
From: tweeters-bounces at mailman1.u.washington.edu
[mailto:tweeters-bounces at mailman1.u.washington.edu] On Behalf Of mike denny
Sent: Saturday, March 08, 2008 10:43 AM
To: Inland NW Birders; tweeters
Subject: [Tweeters] Migration and the back fill theory

Hello All,

Migration is well underway here in southeastern Washington with Long-billed
Curlews, Am. Avocets, Caspian Terns, White-throated Swifts, Says Phoebes,
Savannah Sparrows, Vesper Sparrows and some swallows arriving here this
coming week. Over the last 25 years we have noticed something that has been
much more pronounced with the instant communication of our day and that is
when and where certain bird species are reported first during spring
migration. We have noticed that Tree and Violet-green Swallows, Says Phoebes
and other flycatchers along with many of the passerines are reported way to
the north of us first and it can be up to three weeks before we locate the
same species in this region. So years ago I postulated the "Migratory Back
Fill Theory" which is based on the fact that so many species are first
located hundreds of miles north of us and as the season advances these
populations gradually in fill back to the south at last arriving in our area
south of the Snake River. We are wondering if others that bird east of the
Cascades have observed this? Thank-you.
Later Mike

********************************************************************
Mike & MerryLynn Denny
1354 S. E. Central Ave.
College Place, WA 99324
509.529.0080 (h)

IF YOU HAVEN'T BEEN BIRDING, YOU HAVEN'T LIVED!
*******************************************************************


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