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May 2007

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From:
Bill Whan <[log in to unmask]>
Reply To:
Bill Whan <[log in to unmask]>
Date:
Sat, 5 May 2007 15:28:08 -0400
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Brad Sparks and I birded around Columbus today. Migrants were not
thronging, but we found 24 warbler species, a couple of male summer
tanagers squabbling over territory above the Highbanks MP nature center,
and that there are now two alternate-plumaged laughing gulls off the
boardwalk at the north end of Hoover Reservoir along with maybe a
hundred crappy fishers.
        Clearly something is happening with rose-breasted grosbeaks. There were
crowds of them facing one another off everywhere we found feeders. I've
read of phenomenal numbers, always at feeders, in Ohio and other states
this spring. Brad had an idea that makes sense to me: there aren't any
more grosbeaks than usual, but something in the spring's weird weather
has made some of their customary diet unavailable, forcing them to
depend much more on feeders, hence we humans see far more of them than
usual.
        Killing frosts in early April in the region reduced budding flowers and
leaves. This devastated some fruit crops, and cut back on the leafing
branches attractive to insects. Bent quotes McAtee's 1908 study of 178
sets of stomach contents of this species, observing that its food is
about half and half animal and vegetable. He doesn't give much detail
from McAtee, but relates rose-breasted grosbeaks eat lots of "harmful"
insects (i.e., those that damage plants), and lots of blossoms, fruits,
and buds. As for their diet during spring migration you'd expect that
blossoms and buds would be in especially short supply this spring, and
that the insects that flourish in them would be as well. A promising
hypothesis. Does anyone have any special knowledge to evaluate it? If it
seems to make sense, what other bird species might also be stressed just
about now?
Bill Whan
Columbus

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