VCE wrapped up its 2014 field season with an overnight visit to our Mt.
Mansfield ridgeline study site on Tuesday. Arriving at the upper toll
road parking lot ~5 pm, we were greeted by chilly, damp conditions, but
also by calling Bicknell's Thrushes (BITH), which annually undergo a
resurgence of vocal activity in mid-September. We set up 17 mist nets,
mostly on the Amherst and Lakeview trails, and ran them until dusk.
BITH calls pierced the skies until darkness fell, and a few birds sang
briefly. The frequency and vigor of vocalizing was nowhere near that of
3 months ago, but the chorus was a far cry from the eerily quiet evening
of our visit in late July.
The ridgeline was still bathed in clouds when we returned at 5:45 am to
open nets, and temperatures hovered in the raw low 40s F. BITH put on a
solid dawn chorus, as we heard 16-18 birds total. Swainson's Thrushes
were nowhere to be seen or heard. Our nets started filling, and by noon
we had captured 76 birds. Yellow-rumped Warblers were by far the most
abundant species on the ridgeline, and in our nets, but BITH may have
been second, judging from both captures and birds heard vocalizing. Of
the 13 BITH we mist-netted, 5 were recaptures of adult males from June
and July (one a bird originally banded in 2011). Our total of BITH
captures for 2014 ended up at 57, possibly a single-season record over
our 23 years of banding.
Overall diversity on the ridgeline was low, as we identified only 16
species during the morning, which included 2 Sharp-shinned Hawks and a
single Peregrine Falcon. One unexpected encounter was of 3 Ruffed
Grouse flushed at ~3800 ft elevation on Tuesday evening. Surprisingly,
Black-throated Blue Warblers, which our fall migration banding study in
the mid-1990s showed to be the most abundant transient species on
Mansfield, were almost non-existent - we saw and netted only one bird.
[For a truly scintillating read about our results from that study, check
out http://www.vtecostudies.org/PDF/WB112.pdf].
Our combined capture totals for the 16-17th:
Black-capped Chickadee 1
Bicknell's Thrush 13 (7 immatures, 1 new adult, 5 recaptured adult
males)
Nashville Warbler 1
Blackpoll Warbler 6 (2 immatures, 4 adults)
Black-throated Blue Warbler 1 imm. female
Yellow-rumped Warbler 50 (41 immatures, 9 adults)
White-throated Sparrow 6 (3 immatures, 3 adults)
Dark-eyed Junco 8 (7 immatures, 1 adult)
A final note: there are very few cones on the balsam fir trees (and we
saw or heard no red squirrels), so it's likely that squirrel populations
will again be low in 2015, leading to higher breeding productivity by
BITH and other open-cup nesting species. The biennial "boom-bust" cycle
of cone crops, which has been remarkably consistent across the entire
Northeast for many decades, appears to have broken down in recent
years. Whether this results from climatic changes and/or other
environmental factors, and whether the cycle will self-correct or not,
is unknown. In the short term, the current scarcity of cones in montane
forests appears to be benefitting BITH, which have shown relatively high
recruitment of young birds during the past 3 summers, and probably will
again in 2015.
VCE will be back at it again next June, so stay tuned.
Chris
--
Chris Rimmer
Vermont Center for Ecostudies
P.O. Box 420
Norwich, VT 05055
802-649-1431 ext. 1
www.vtecostudies.org
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