The VCE crew made its final 2015 foray to Mansfield's ridgeline on
Tuesday evening, hoping to intercept some passage migrants and hear
the Bicknell's Thrush (BITH) parting chorus. The trip was a success
on both counts. We left the valley's stifling heat and arrived at
our study site - the toll road uppermost parking lot - at ~5 pm,
with cooler temperatures and a surprisingly brisk west wind. We
scurried about setting mist nets and had 23 open by 6:30 pm. In
typical mid-September fashion, BITH put on a solid show at dusk, as
18-20 birds vocalized with vigor over ~15-20 minutes. We even heard
a brief snatch of song from one individual. Among the 10 birds we
captured before closing nets as darkness fell, the most surprising
by far was a male Wilson's Warbler, the first we have ever
encountered on Mansfield, even during the three autumns we banded on
the ridgeline from 1995-97. We also captured 3 BITH, one an adult
male we had banded in mid-July, and two young-of-the-year.
The season's reduced daylength afforded us an opportunity to sleep
in, and we reopened our nets at the leisurely hour of 5:30 am.
Again, BITH vocalized as they did back in July, though only calls
were heard, from the same (presumably) 18-20 birds. Why BITH undergo
this annual resurgence of calling just prior to their southward
departure (most will be gone by October 1) is anyone's guess. For a
species that doesn't hold true breeding territories, there would
seem to be little imperative to restake claim to any turf, in hopes
of reoccupying it next spring. Both male and female adult BITH
return to Mansfield at relatively high rates, so perhaps there is
some social context/message we humans can't decipher. Other
songbirds are known to resume limited vocalizing (usually song) in
fall, but I'm not aware of any that do so to the same extent as
BITH. Hormones are likely involved, perhaps triggered by
daylength(?). Whatever the cause/reason, it's a delight to hear,
when all other species are virtually silent! Birds continued to call
sporadically throughout the morning, some of them quite insistently.
Overall, we captured 82 birds in our nets. In numerical abundance,
they included:
Yellow-rumped Warbler - 29 (all new)
Bicknell's Thrush - 15 (10 new birds [7 young, 3 adults] and 5
recaptures [4 from earlier in the summer, 1 banded as an adult on 12
Sept 2011 and not encountered since!])
Black-throated Blue Warbler - 13 (all immatures. This species was by
far the most abundant non-locally breeding species during our
mid-1990s autumn banding study. Of the 338 individuals we banded i
those 3 years, 328 [97%] were immatures, and not a single one was
ever recaptured on site. We believe montane forests are an important
habitat for post-fledging dispersers, but the fact that birds appear
to rapidly depart is puzzling. If you can't bear not to learn more,
check out our 2000
paper in the Wilson Bulletin.)
Golden-crowned Kinglet - 5
White-throated Sparrow - 4 (including 3 recaptures of adults from
June-July)
Dark-eyed Junco - 4
Ruby-crowned Kinglet - 2
Blackpoll Warbler - 2
Red-breasted Nuthatch - 1
Brown Creeper - 1
Swainson's Thrush - 1
Ovenbird - 1
Nashville Warbler - 1
Magnolia Warbler - 1
Black-throated Green Warbler - 1
Wilson's Warbler - 1
We'll be back up there in early June of 2016 to launch our 25th
consecutive year of field work. Until then, safe journeys to all the
migrants!
Chris
--
Chris Rimmer
Vermont Center for Ecostudies
P.O. Box 420
Norwich, VT 05055
802-649-1431 ext. 1
www.vtecostudies.org