[EBB Sightings] New info on Anna's

	<151811.81227.qm at web80608.mail.mud.yahoo.com>

On Sun, 9 Sep 2007 23:42:36 -0700 (PDT), "Verne Nelson"

>In the late
>1970s, ornithologists decided that those notes came
>from the birds' vocal organs. Chris Clark and Teresa
>Feo of the University of California, Berkeley have
>challenged that idea by removing some birds' outer
>tail feathers. A clipped male still dives, but he no
>longer makes the sound as he bottoms out. 

I remember talking to the late Louis Baptista about this.  He was able to
show via sonograms, that the dive-pop of Anna's Hummingbird was virtually
identical to a popping sound included as part of Anna's Hummingbird song.
It was just much louder.

This view that the sound must be vocal was widely accepted, but I was never
convinced.  I voiced my skepticism publicly whenever given a chance.  If
the sound were vocal, why did we never hear the loud dive-pop when the bird
was perched?  Why would this species give this sound only in the middle of
a high-speed gymnastic display?  It didn't make sense.

Earlier ornithologists noted the oddly shaped outer rectrices and thought
they produced the dive-pop.  One experimenter glued the tail feathers to
the end of a whip and claimed to be able to make the dive-pop sound by
whipping the feathers through the air.  Unfortunately others were unable to
reproduce those results.

I have suggested many times, that the way to get at the truth would be to
experiment with diving male Anna's Hummingbirds and remove the outer
rectrices to see if they still pop.  Finally somebody has done this and the
results are hardly surprising.  Many of us have noticed that male Anna's
Hummingbirds in heavy tail molt do not make the dive-pop sound.

So the similarity in the sonograms between the dive-pop and other popping
sounds made vocally is just coincidental.  I'm delighted that the truth of
this seemingly simple question has finally been resolved.

-- 
Joseph Morlan, Pacifica, CA 94044   jmorlan (at) ccsf.edu 
Fall Birding Classes start Sept 5   http://fog.ccsf.edu/~jmorlan/
California Bird Records Committee   http://www.wfo-cbrc.org/cbrc/