Again this week, a belated report from VCE's final summer field trip to our
long-term study site on the Mansfield ridgeline. We arrived in early
evening on the 27th and set up 28 mist nets under ideal conditions - barely
a breath of wind, warm, patchy cloud cover. Vocal activity was markedly
lower than a week earlier, with very few birds calling or singing, and no
noticeable dusk "chorus". Singing consisted solely of a few snatches from
robins and white-throats. Only a handful of Bicknell's Thrushes (BITH)
called, none sang, and not a peep was heard from any Swainson's Thrushes.

By nightfall we had captured a nice assortment of 15 birds that included 7
BITH (6 juveniles and a new adult female). The evening's undisputed
highlight was a juvenile N. Saw-whet Owl that elicited oohs and aahs from
our several visitors. Its bill-snapping belied a docile nature in the hand,
and we all watched it fly silently off in near-full darkness with a new
size 4 band on its feathered tarsus.

Expectations for a busy morning of netting fell flat, though the first 2-3
hours saw steady action. Despite continued calm winds, temps in the
mid-60sF, and cloud cover, activity was light. Few birds vocalized, and the
ridgeline was very quiet overall. Many adults are now in flight feather
molt, which helps to explain their limited movements, but we were surprised
not to capture more free-flying juveniles. We caught only a handful of
birds after 9 am and closed our nets at noon with a total of 46 birds over
our combined evening-morning session.

Our biggest surprise was finding 2 adult female Tennessee Warblers
simultaneously in adjacent nets. This boreal breeder (not confirmed to nest
in VT during the 2003-2007 Breeding Bird Atlas) is well known for its
unusual tendency to disperse south of its Canadian breeding range in early
summer and to actively molt flight feathers while migrating. One of the two
females we captured had dropped its innermost two primaries on each wing.
Other non-local captures included two juvenile Hermit Thrushes and our
third Blackburnian Warbler of the summer.

Northern Saw-whet Owl  1 juvenile
Yellow-bellied Flycatcher  2 juveniles
Bicknell's Thrush  13 (1 new adult female, 10 new juveniles, 2 retrap
Swainson's Thrush  1 yearling male
Hermit Thrush  2 free-flying juveniles
American Robin  2 free-flying juveniles
Tennessee Warbler  2 adult females caught simultaneously, 1 in early
primary molt
Blackburnian Warbler  1 immature
Blackpoll Warbler  3 (2 new adult females, 1 retrap adult male)
Yellow-rumped Warbler (Myrtle)  4  (1 return adult male, 1 retrap adult
female, 2 juveniles)
Dark-eyed Junco (Slate-colored)  10 (2 new adult females, 2 repeat males, 6
White-throated Sparrow  5 (3 new adult males, 2 juveniles)

We haven't had time yet to fully summarize the season's results, but we had
>450 captures between mid-May and late July, a higher number than in most
years. Over the past 3 summers, raw numbers of adult captures of three
target species show no consistent trend. For any kind of meaningful
comparison among years, our totals have to be examined against the number
of annual net hours (an indication of effort). This summer's spike in
Blackpoll Warbler numbers - especially of males - is difficult to explain,
but encouraging.

2014 2015 2016
Bicknell's Thrush 45 (30M, 13F, 2U) 42 (26M, 15F, 1U) 35 (24M, 11F)
Swainson's Thrush 19 (15M, 4F) 12 (10M, 2F) 23 (20M, 3F)
Blackpoll Warbler 33 (23M, 10F) 28 (13M, 15F) 50 (33M, 17F)

(M=male, F=female, U=unknown sex)

We'll provide a more coherent summary soon. This was the third consecutive
season of non-existent red squirrel numbers on Mansfield, and numbers of
yearling birds (an indication of productivity in the preceding summer)
reflected it. Among known-age birds, we captured 14 yearling to 21 older
(2+) adult BITH, while this ratio was 17:6 in Swainson's Thrush and 26:21
in Blackpoll Warbler. Cone crops are again very light this summer, and the
record 15 juvenile BITH we caught likely foretell strong recruitment again
next summer.

We'll make a final foray in mid-September to wrap up our 2016 field season
and will report back then.


Chris Rimmer
Vermont Center for Ecostudies
PO Box 420 | Norwich, Vermont 05055
802.649.1431 x1