Kevin:

It could be that I misunderstood what exactly the sound was that Leah and
her son were hearing. I don't know what a "light sabre" sounds like so we
may be talking about entirely different sounds, but we definitely hear low
frequency wing noise during late molt. I believe the sound we are hearing
is not related to Doppler shift, as it is constant in pitch whatever the
bird's distance and velocity. Only the volume changes as it moves closer,
passes, and moves away.

I'll have to pay more attention to hear what you are describing.

chuck reinsch
magnolia, seattle, wa
creinsch at humbirds.org

----- Original Message -----
From: "Kevin Purcell" <kevinpurcell at pobox.com>
To: "Leah Wegener" <dlwegener at msn.com>
Cc: "Kevin Purcell" <kevinpurcell at pobox.com>; "Tweeters"
<tweeters at u.washington.edu>
Sent: Saturday, December 15, 2012 12:27 PM
Subject: Re: [Tweeters] Hummingbird wing noise question


Some thoughts and observations.

I think it's just the "fundamental" from the wing motion throwing vortexes
off the wings.

There are two vortexes shed per wing per beat in hummingbirds, one on the
upstroke and one on the downstroke as the wings move in figure 8 in "hover
mode" flight. That "powered upstroke" is a clever optimization for hovering.

It's a low frequency sound and the vortexes only maintain the structure over
a short distance so you have to be quite close to hear it. I've found
sitting in a garden amongst flowers is good. I do it in the Thomas St
P-patch and get close "listens" when reading when the resident Anne's
appears.

If it is generated solely by wing motion it's not gender specific but the
frequency might be (different wing lengths; different body weights). I
suspect an observational bias in observing only a male on his territory
might give that impression. :-)
I doubt it has anything to do with molt as I hear it every time the same
hummer gets close to me over a period of months.

Initially I though the "light saber" effect is Doppler shift from motion.
But on thinking about it that would only shift the pitch a small amount at
reasonable speeds (~1% at 3 meters per second). I wonder if it's a change in
flight style or power that directly changes the wingbeat frequency as the
bird moves from a hover to hover + directional flight. If it's the latter
you would expect the pitch to increase as it moves away from you (the
opposite of the Doppler effect).

Seems like an area of research waiting to be done. Perhaps by a birder with
one or more mics at a humming bird feeder connected to a computer to record
sound with a video camera or human with a notebook to note behavior and
location. With a high speed camera one could see the changes in beat
frequency and match them to changes in the sound.

On Dec 13, 2012, at 5:23 PM, Leah Wegener wrote:

> Hi, Tweets,
> Is it true that only male hummingbirds make the VW engine noise with their
> wings, the noise that sounds kind of like a light saber? My son observed
> this in our yard but we cannot find any information that backs this up.
> I'm not thinking of the mating flight swoop, but just the everyday flying.

--
Kevin Purcell (Capitol Hill, Seattle, WA)
kevinpurcell at pobox.com | at kevinpurcell
http://kevinpurcell.tumblr.com
http://flickr.com/photos/kevin_g_purcell




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