arf@ddsw1.MCS.COM (Jack Schmidling) (07/25/90)
HEAD JERKING OF WALKING BIRDS
I don't know what group this subject was recently discussed
in, so if I missed it, please let me know.
There were a number of theories as to why walking birds move
their head forward and back in synch with footsteps.
I don't even recall which one seemed most reasonable, but I
have another input that can only send everyone back to the
drawing board.
I kidnapped a dove nestling and hand raised it for the
purpose of confusing the rec.bird newsgroup's indoor/outdoor
business.
Well, it has been most interesting. The bird was released
several weeks ago and seems equally at home outside or
inside. Some nights it sleeps outside, others on the back
porch. Right now, as I type, it is sitting on my head.
Not only does this bird jerk its head while walking, but it
jerks its head when I walk, with the bird sitting on my
finger.
What is most interesting about this behavior is that he only
does it when looking in the direction that I am walking. If
he faces me or the direction from which we are coming, his
head does not move. I have held him out at arms length to
make sure it wasn't just my body, close to him, that was
filling his field of view.
So, back to the drawing board?
yackob@eeserv.ee.umanitoba.ca (Kerry Yackoboski) (07/27/90)
In article <1990Jul25.021150.14574@ddsw1.MCS.COM> arf@ddsw1.MCS.COM (Jack Schmidling) writes: > HEAD JERKING OF WALKING BIRDS > > I don't know what group this subject was recently discussed > in, so if I missed it, please let me know. > There were a number of theories as to why walking birds move > their head forward and back in synch with footsteps. > I kidnapped a dove nestling and hand raised it for the > purpose of confusing the rec.bird newsgroup's indoor/outdoor > business. > > Well, it has been most interesting. The bird was released > several weeks ago and seems equally at home outside or > inside. Some nights it sleeps outside, others on the back > porch. Right now, as I type, it is sitting on my head. > > Not only does this bird jerk its head while walking, but it > jerks its head when I walk, with the bird sitting on my > finger. > > What is most interesting about this behavior is that he only > does it when looking in the direction that I am walking. If > he faces me or the direction from which we are coming, his > head does not move. I have held him out at arms length to > make sure it wasn't just my body, close to him, that was > filling his field of view. > Might it be that the bird sees motion better than still objects, and when it is walking forward (or when you are walking it) it wants maximum vision? Could it be an attempt to emulate Chuck? :-) -- Kerry Yackoboski <yackob@eeserv.ee.umanitoba.ca> The Scanning Tunneling Microscopy Laboratory in the Cellar U of Manitoba, Winnipeg, Canada
phz@cadence.com (Pete Zakel) (07/27/90)
I always assumed birds jerked their heads so that most of the time their
heads (and therefor eyes) were stationary with regard to surroundings for
the majority of the time. When I've watched birds closely, they jerk
faster when they walk faster, and during the non-jerking portion the head
remained stationary w/r/t the surroundings. I assumed this was to make
seeing easier.
-Pete Zakel
(phz@cadence.com or ..!{hpda,versatc,apollo,ucbcad,uunet}!cadence!phz)brian@ncrorl.Orlando.NCR.COM (brian) (07/27/90)
There's been a bunch of discussion about the jerking head. Pete, I think you're almost home. I've been taught that the head bobing/jerking is so that the bird can perceive in 3-D. By using the disparagy (sp??) in the two images, it can synthesize the 3-D depth perception that we all know and need! Since they cannot focus with both eyes on a singular subject, this is their way of getting the parrellax view... brian "His job is to shed light, not to master!!!"
gregory@agcsun.UUCP (Gregory Bloom) (07/31/90)
:1144 In article <1990Jul26.181953.17452@ccu.umanitoba.ca> yackob@eeserv.ee.umanitoba.ca (Kerry Yackoboski) writes: >In article <1990Jul25.021150.14574@ddsw1.MCS.COM> arf@ddsw1.MCS.COM (Jack Schmidling) writes: >> HEAD JERKING OF WALKING BIRDS >> >> There were a number of theories as to why walking birds move >> their head forward and back in synch with footsteps.... > > Might it be that the bird sees motion better than still objects, >and when it is walking forward (or when you are walking it) it wants >maximum vision? Could it be an attempt to emulate Chuck? :-) > I believe that birds eyes do not constantly wiggle to avoid saturating the receptors (eye wiggle == nystigmus?), so when their heads are still, images that don't move will quickly 'bleach-out' the receptors they fall on. This means that when a birds head is still, it only sees things that are moving, which is probably a real good way to spot incoming predators and worms and such against a complex background. The way a bird can maximize this sort of motion detection is by moving its head in quick jerks as it walks, giving about an 80% duty cycle to frozen-eyed motion detection. Gregory Bloom agcsun!gregory@boulder.colorado.edu