Mountain meather has not been our ally this spring and early summer.
This week's Tuesday-Thursday mist-netting stint on the Mansfield
ridgeline featured the now-expected mix of swirling clouds, wind, and
intermittent rain. Our session wasn't a complete wash-out, as we were
able to run nets much of the time, but captures were sparse overall.
Based on the condition of female incubation/brood patches, it appears
that most species are still actively nesting. Winter Wrens (an
early-nesting species) were the only persistent singers. Bicknell's
Thrushes were very quiet, with just a brief burst of vocalizing at dusk.
So far this season, we have captured 25 individual Bicknell's Thrushes
on the Mansfield ridgeline, a number that is about "normal". However,
we have had fewer returning banded birds (i.e. those banded in previous
years). Of 25 mist-netted individuals, 18 have been males and 7
females. There is a preponderance of yearling birds (13 males, 3
females), reflecting last summer's solid production in the absence of
red squirrels and other predators (I saw the season's first squirrel on
Wednesday). We recaptured one 10 year-old male thrush at the far
northern edge of our study area, our first encounter with it since 2004.
Many birders, including Mountain Birdwatch field workers who are
counting high-elevation birds all over the Northeast, have commented on
how quiet the montane forest was in June. We've observed the same on
Mansfield and suspect that the frequently inclement weather is in part
responsible. Although montane forest birds and other wildlife are
adapted to relatively harsh weather conditions, we can't help wondering
about the effects of this year's weather on nesting success. In past
years (this is our 20th on Mansfield), we have witnessed nestling
abandonment and death following prolonged spells of bad weather. We
assume that when adults become stressed by the elements, they may be
unable balance their own energetic needs with those of their young,
causing nestlings to die of exposure. We have several times found
Bicknell's Thrush and Blackpoll Warbler nests with dead young, only
later to confirm that the females were alive and well. When times are
tough, it generally pays a relatively long-lived bird (if you consider
several years to constitute a long life...) to ensure its own survival
at the expense of current reproduction, so that it can live to breed again.
VCE is working with our long term datasets from Mansfield and other
Vermont mountains to understand annual variation in local weather
patterns, how they impact avian survivorship and productivity, and how
they might relate to potential future climate changes. We'll be back on
Mansfield in two weeks, hoping to observe and capture fledglings of
different species, but wondering if that will be the case.
Chris Rimmer and Kent McFarland
Vermont Center for Ecostudies
P.O. Box 420
Norwich, VT 05055
802-649-1431 ext. 1