Date: 1/13/18 9:02 am
From: Lars Per Norgren <larspernorgren...>
Subject: [obol] Crossbill conundrum solved , for me at least
For years I have marveled at how I often hear a "flock" of crossbills, but
if I locate the source of the sound overhead, I see one bird. I have surely been
hearing multiple birds. There remained a strong intuitive urge to only count one
bird, despite my having heard more. It turns out some crossbill flight calls are polyphonic-
multiple parts of the voice box are used simultaneously. I see in the sonogram
of Type I that it makes three equally strong notes, absolutely simultaneously. I haven't
gone further to look at other types. So I'm not claiming to have heard Appalachian
Crossbills in Oregon. But it is perfectly normal for one crossbill to sound like three.
Apparently some thrush songs work this way as well. lpn
 
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