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Chris,

Thanks for the informative report. I had figured that if anyone knew the
habits of these guys, it would be you. It's interesting to note that these
southbound (more or less) birds would be singing. Are most of the summer
reports of singing birds? In any event, I won't get back to the site for
several days, but I'll keep an eye on him.

Bryan



Date: Sun, 7 Jul 2002 09:10:08 -0400
From: Chris Rimmer <[log in to unmask]>
Subject: Tennessee Warblers
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Interesting report of a Tennessee Warbler by Bryan. This is an intriguing
species that annually shows up well south of its normal breeding range in
early summer, with males often singing. Having studied them via banding in
James Bay, Ontario (where they are one of the most abundant breeding
warblers) 20 years ago, I documented a mass exodus in late June and
early-mid July each year, of both males and females still in breeding
condition. These were invariably unbanded birds (i.e. not from my
immediate study site), and I never recaptured a single one. I assumed they
were mostly failed breeders beginning their southward flight. Tennessee
Warblers (TEWAs) have a very unusual post-breeding molt strategy, in that
many birds initiate their molt during migration, rather than completing it
on the breeding grounds as do most other long-distance migrants. Many
banding stations like VINS' in Woodstock routinely capture adult TEWAs in
various stages of their molt, including some birds which are molting flight
feathers so heavily that it would seem impossible they could be migrating.
Few if any of these individuals are ever recaptured, suggesting that they
continue to move while undergoing their molt. An interesting twist is that
some TEWAs (probably successful breeders) do remain on the northern nesting
grounds and complete their prebasic molt before migrating, so the species
has a dual, or plastic, molt strategy. As far as I know, no other wood
warbler, and really no other long-distance NA passerine, has a similar
system.
So, these early summer TEWAs are most likely failed breeders, or
non-breeders, that have departed the boreal zone and will begin their molt
down here. Why the males sing is a good question. Maybe hormones simply
haven't subsided yet. The first VT Breeding Bird Atlas did confirm nesting
by this species in VT, both in the NE Kingdom and so. Green Mts (Lye Brook
Wilderness Area), but I'm not aware of any recent reports that suggest
breeding. It will be interesting to document the breeding status of TEWA
in the second statewide atlas, due to begin next summer.
Chris

Chris Rimmer
Vermont Institute of Natural Science
27023 Church Hill Road
Woodstock, VT 05091
802-457-2779 ext. 120
<www.vinsweb.org>




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