I'll add my two cents by agreeing 100% with what Chris Hill wrote. With
humans on the telephone, their voices signal unmistakeably "human," then I
guess we distinguish them by "voice quality.". As soon as you get into
related (or sometimes not related) species of birds, that "voice quality"
can sound awfully similar, perhaps because we aren't attuned to hear the
voices of other species as we are our own.

To distinguish birds, we end up using attributes that can easily be
*quantified,* such as pitch, number of notes, relative length of notes,
ascent vs. descent within or between notes, and others. We don't recognize
our friends' voices by such quantification, in part because we have to
learn the often minor differences in voice tone and accent. We do use
pitch, but the difference between a high-pitched and a low-pitched human
voice is nothing like the range in birds--say, between a Yellow-breasted
Chat's and a Blackburnian Warbler's song.

To recognize the voices of different Red Crossbill "species," I have to
know whether the call goes up or down at the end and whether it has a burry
sound (more complex figure in a sonagram). But there is also plenty of
variation within species of birds, just as in human voices, and we should
be able to recognize individual birds by their voices ("voice quality,"
presumably). For the most part I don't think we can do this, although such
differences show up well in sonagrams.

It would be nice if we could include graphics more easily in these
discussions, as, for evidence, we could show a bunch of human voice prints
vs. the songs of a few related bird species, just to see how similar or
different they are. I really would love to see a sonagram of 25 humans,
each saying "The quick brown fox sparrow jumps over the lazy gadwall."

And I'm willing to guess that we're all correct, and that there are some
semantic problems associated with "voice quality" as Teresa, Harriet, Chris
and I individually envision the term.

I'll second Chris's comments about knowing the size of a bird because you
know what the bird is! Although I think we, being reasonably intelligent
animals, also have the ability to judge the size of a bird by its
surroundings. I once found a pygmy Red Knot and followed it around, trying
to get a photo of it when it approached a discarded beer bottle (for
scale), but it wouldn't cooperate. I watched it by itself for several
minutes and never had any doubt that it was smaller than usual. I never
knew there were pygmy birds, but last year I saw a juvenile Baird's
Sandpiper, typical in every way except that it was about the size of the
Western Sandpipers with which it foraged.

It's all too easy to twist a thread into a segue.....

Dennis Paulson, Director phone: (206) 756-3798
Slater Museum of Natural History fax: (206) 756-3352
University of Puget Sound e-mail: dpaulson at ups.edu
Tacoma, WA 98416