[obol] Re: Local Swainson's Thrush Fallout
- From: David Irons <llsdirons@xxxxxxx>
- To: Jim Danzenbaker <jdanzenbaker@xxxxxxxxx>, Gerard Lillie <gerard.lillie@xxxxxxxxxxx>
- Date: Fri, 30 Aug 2013 17:25:36 +0000
Answering Jim Danzenbaker's question about lingering Warbling Vireos:
The western subspecies of Warbling Vireo is a "molt migrant," which means they
leave the breeding grounds, make a partial southbound migration, find a spot
with a good food supply (perhaps Jim's backyard), then stop for a few weeks to
complete their fall prebasic molt (replacement of all feathers). Once the molt
is completed, these birds resume their southbound migration to their wintering
grounds. The molt migrant molt/migration strategy seems to be more prevalent
among populations of birds in western North America and is believed to be an
adaptation to food and water supplies that often dry up (literally) on their
breeding grounds. In eastern N. America, it is much more humid and there are
summer thundershowers and rains that keep the breeding areas wet through the
summer, so eastern populations of these species have not had to adapt. Eastern
Warbling Vireos and Willow Flycatchers, along with Rose-breasted Grosbeak (the
eastern equivalent to our Black-headed Grosbeaks) go through their prebasic
molt before they leave the nesting grounds.
Western riparian species like Warbling Vireo, Willow Flycatcher, and
Black-headed Grosbeak (three of the best-known western molt migrants) typically
nest in areas that are quite wet when they arrive in the spring. As Summer
progresses, many small streams and seasonal wetlands go dry, thus there are no
longer insect hatches and other food sources that will sustain these birds as
they go through an energy intensive molt. Since they have to replace their
flight feathers before making long flights south, they have to find a food
source that will power the molt process. For a seed-eating bird like a
Black-headed Grosbeak, this may be your backyard bird feeder or the sunflowers
growing in your garden. If you have a vegetable garden that you regularly water
this time of year, be on the lookout for Willow Flycatchers hanging out in your
yard for several days. We use to get them every August in our Eugene backyard.
I've been hearing Black-headed Grosbeaks daily around the neighborhoods where I
work in McMinnville. They will around for another week or so and mostly gone by
about the 10th of September.
Dave IronsPortland, OR
Date: Fri, 30 Aug 2013 09:25:22 -0700
Subject: Re: [obol] Re: Local Swainson's Thrush Fallout
From: jdanzenbaker@xxxxxxxxx
To: gerard.lillie@xxxxxxxxxxx
CC: llsdirons@xxxxxxx; obol@xxxxxxxxxxxxx
All,
I've been having audible nocturnal Swainson's Thrushes over my house every
night and early morning since last Friday morning but none more prominent than
the flight of August 25. I've had Swainson's Thrushes every morning around the
yard - usually with several running along the railing of the back deck. Just a
few blurps this morning so the line of Thrushes may have shifted westward? I'm
in Battle Ground which is about 6 miles east of the I-5 freeway in Clark
County. The number of vireos/warblers/flycatchers in and around the yard
continues to be the best I've ever had with a minimum of 8 Warbling Vireo each
day. Don't know if these are the same individuals as the number of
Black-throated Grays, Yellows, OCs, and Wilson's seems to noticeably fluctuate.
Anybody have any idea whether WAVIs linger more at one spot during migration
than other species? My local BH Grosbeaks left on the 8/26 or evening of the
25th, the day after I had an incursion of four more BHGR to add to my two
lingering locals. Anybody else lose their BH Grosbeaks on the 26th?
Difficult to sleep during fall migration!
Keep your eyes and ears skyward.
Jim in Battle Ground, WA
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