arf@ddsw1.MCS.COM (Jack Schmidling) (07/28/90)
Subject: Re: HEAD JERKING OF WALKING BIRDS I have a problem with Pnews here in that it makes it look like I want responses in email when I really want to discuss things on the net. The following is typical of the responses I got to the question I posed.... >You realize, of course, that this is a violation of Federal law. ............. >If it is one of the species you can legally possess, let me know, and I will comment on your behavioral questions. ............ I fully accept the criminal nature of the act which I implicated myself in, but having watched a kestral snatch the first two fledglings off the nest in my bathoom window, I was in no mood to concern myself with the letter of the law. The most amusing response (excerpt above) was from someone who refused to even discuss the issue if the bird in question was a mourning dove. ............ One responder suggested that the behavior was an adjustment for continually changing focal distance. This seems like a reasonable answer but I can't help but wonder why these birds have such a limited depth of field. One assumes that it must be on the order of 1/2 inch because that amount of head movement seems to put things right again. I suppose the answer lies in what fantastic things they must be able to see in that very restricted range. A few more experiments with the bird at arms length, seem to support the focus theory. If I was very careful to make sure he could not see me, he did seem to jerk his head no matter which way he was facing. ................. On a slightly different point, is there really any way of knowing what a bird is looking at? For example..... He will suddenly cock his head and look straight down at the floor and........... However, someone on the opposite side of the bird would swear that he was looking straight up in the air. ...... just heard the familiar wing beat and find Charlie in the bucket of sunflower hearts on the back porch. For the past five days, he has left around dark and returns late in the morning to "visit". Oh! Oh! the doorbell.... must be the bird police. Run Charlie! ............... If you insist on sending email, please send to arf@gagme NOT to the address in this header.
john@nmt.edu (John Shipman) (07/29/90)
Jack Schmidling (arf@gagme) writes: +-- | The following is typical of the responses I got to the | question I posed.... | | >You realize, of course, that this is a violation of Federal law. +-- The federal Migratory Bird Treaty prohibits any individuals from possessing wild native birds without a permit. Introduced birds such as Rock Doves (park pigeons), European Starling, Budgerigar, etc., are not included in this law. (By the way, starlings make terrific cagebirds.) +-- | I fully accept the criminal nature of the act which I | implicated myself in, but having watched a kestral snatch | the first two fledglings off the nest in my bathoom window, | I was in no mood to concern myself with the letter of the | law. +-- Typical prejudice against birds of prey---the kestrel was probably feeding young! Raptors have to eat too. No smiley here---I'm not shy about being a predator fan; a bumper sticker on my car reads, ``Save the Great White Shark.'' -- John Shipman/Zoological Data Processing/Socorro, NM/john@jupiter.nmt.edu ``Let's go outside and commiserate with nature.'' --Dave Farber
afsipmh@cid.aes.doe.CA (Patrick Hertel) (07/30/90)
In article <1990Jul28.033019.5059@ddsw1.MCS.COM> arf@ddsw1.MCS.COM (Jack Schmidling) writes: > > > Subject: Re: HEAD JERKING OF WALKING BIRDS > > I believe that the head jerking is due to the fact that a bird's eye is fixed and therefore it has to move its head to "refresh" its receptors. It would explain why the head jerk is not necessary when the bird is carried and looking off to the side. -- Pat Hertel Canadian Meteorological Centre Analyst/Programmer 2121 N. Service Rd. phertel@cmc.aes.doe.ca Dorval,Quebec Environment Canada CANADA H9P1J3
chrish@videovax.tv.tek.com (Chris Hawes) (08/01/90)
> I believe that the head jerking is due to the fact that a bird's eye is >fixed and therefore it has to move its head to "refresh" its receptors. >It would explain why the head jerk is not necessary when the bird is carried >and looking off to the side. >-- >Pat Hertel Canadian Meteorological Centre I'll buy that. Pat, if that's "known" fact, it sure sounds like it. Thanks for the best answer I've read so far on this question. Does anyone out there know about the difference in these walking bird eye receptors as compared to non-walking bird eye receptors? chris at Tektronix TV Meas. Sys. "... We gotta move these color TV's" Dire Straights
keithl@loop.uucp (Keith Lofstrom;;;646-6296) (08/02/90)
I got here late; sorry if this has already been suggested: Birds have small brains, and can't distinguish between their own motion and the motion of the predators they are trying to avoid. If you watch the head closely, it holds still while the bird's body continues forward, then jerks forward to a new fixed position. This feeds a series of stationary images to the bird's brain, and makes moving objects in the visual field more obvious. Why doesn't a bird's head move when riding on a shoulder? Birds didn't evolve to ride on shoulders; the built-in reflexes are wrong. -- Keith Lofstrom keithl@loop.uucp ...!sun!nosun!loop!keithl (503)628-3645 KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon" Design Contracting in Bipolar and CMOS - Analog, Digital, and Power ICs
mjm@oliven.olivetti.com (Michael Mammoser) (08/06/90)
In article <1990Jul28.033019.5059@ddsw1.MCS.COM>, arf@ddsw1.MCS.COM (Jack Schmidling) writes: > > I fully accept the criminal nature of the act which I > implicated myself in, but having watched a kestral snatch > the first two fledglings off the nest in my bathoom window, > I was in no mood to concern myself with the letter of the > law. What was it that you thought you were accomplishing? It seems that there are two possible consequences of your action. You deprive a kestrel of a meal and: (a) the kestrel, not being able to nourish itself, dies. Now you have a dead kestrel rather than a dead dove. Do you place an intrinsically higher value on doves than kestrels? (b) the kestrel goes off and takes some other bird. Now you have some other bird dead rather than a dead dove. Are doves worth more than some other species? What if the other bird taken was also a dove? Just what were you accomplishing? > One responder suggested that the behavior was an adjustment > for continually changing focal distance. This seems like a > reasonable answer but I can't help but wonder why these > birds have such a limited depth of field. One assumes that > it must be on the order of 1/2 inch because that amount of > head movement seems to put things right again. One of the best theories that I've heard is that the bird does this to provide the parallax necessary to make distance judgements. Animals with binocular vision, such as people, view objects with both eyes at the same time. Since the eyes are separated by some distance, the position of the object with respect to the distant background is different in each eye. This difference (parallax) is the way that we make accurate judgements of the distance that the object is at. Birds with monocular vision are viewing a distant object with only one eye. They bob their heads back and forth to shift the position of their eye in order to provide this parallax. Sounds logical anyway. Mike
sonny@charybdis.harris-atd.com (Bob Davis) (08/06/90)
In article <63474@oliveb.atc.olivetti.com> mjm@oliven.olivetti.com (Michael Mammoser) writes: > >This difference (parallax) is the way that we make accurate >judgements of the distance that the object is at. Birds with >monocular vision are viewing a distant object with only one eye. >They bob their heads back and forth to shift the position of >their eye in order to provide this parallax. Sounds logical anyway. > >Mike > NO, NO, NO. As another poster to this thread has already accurately observed, THE HEAD IS RENDERED ABSOLUTELY IMMOBILE RELATIVE TO THE EARTH by the bird's "head bobbing" motion as it walks. Look at it closely. I often have marvelled at just how totally motionless the bird is able to hold its head as it walks. What an effective biological servo control system this is! ______________________________________________________________________________ Bob Davis \\ INTERNET : sonny@trantor.harris-atd.com | _ _ | Harris Corporation, ESS \\ UUCP : ...!uunet!x102a!trantor!sonny |_| |_| | | Advanced Technology Dept.\\ AETHER : K4VNO |==============|_/\/\/\|_| PO Box 37, MS 3A/1912 \\ VOICE : (407) 727-5886 | I SPEAK ONLY | |_| |_| | Melbourne, FL 32902 \\ FAX : (407) 729-2537 | FOR MYSELF. |_________|
mjm@oliven.olivetti.com (Michael Mammoser) (08/09/90)
In article <4082@trantor.harris-atd.com>, sonny@charybdis.harris-atd.com (Bob Davis) writes: > In article <63474@oliveb.atc.olivetti.com> mjm@oliven.olivetti.com (Michael Mammoser) writes: > > > >This difference (parallax) is the way that we make accurate > >judgements of the distance that the object is at. Birds with > >monocular vision are viewing a distant object with only one eye. > >They bob their heads back and forth to shift the position of > >their eye in order to provide this parallax. Sounds logical anyway. > > > >Mike > > > NO, NO, NO. As another poster to this thread has already > accurately observed, THE HEAD IS RENDERED ABSOLUTELY IMMOBILE > RELATIVE TO THE EARTH by the bird's "head bobbing" motion as it walks. > Look at it closely. NO, NO, NO! The bird can hold its head absolutely immobile only in so far as it can stretch its neck. Once the neck is stretched as far as it can go, if the bird continues walking, the head MUST become mobile. Actually, the poster was differentiating between the bird continuously moving its head back and forth while it stepped, and holding the head stationary while it stepped and moving it forward at the end of the step. No matter what the method, it has no bearing on the idea that I put forth. However, here are some references that I found concerning head bobbing. Bent's Life Histories of North American Gallinaceous Birds On the Key West Quail-Dove, Audubon (1840) writes: "...and it moves its neck to and fro, forward and backward, as pigeons are wont to do." Bent's Life Histories of North American Blackbirds "The gait of the Brewer's Blackbird is usually a walk, accompanied by short forward jerks of the head. When the bird runs there is no jerk. Mulford (1936) outlines the process of taking two walking steps as follows: '1. Head is thrust forward as one leg and foot are lifted. This moves the center of balance forward. 2. Leg and foot are brought forward. 3. Head is pulled back as body is brought forward by step and as foot is set down on ground. 4. The sequence of movements is repeated with other foot.' " On 30 Jul 90, Pat Hertel writes: "I believe that the head jerking is due to the fact that a bird's eye is fixed and therefore it has to move its head to "refresh" its receptors." On 30 Jul 90, Gregory Bloom writes: "I believe that birds eyes do not constantly wiggle to avoid saturating the receptors (eye wiggle == nystigmus?) (sp), so when their heads are still, images that don't move will quickly 'bleach-out' the receptors they fall on." On 1 Aug 90, Keith Lofstrom writes: "Birds have small brains, and can't distinguish between their own motion and the motion of the predators they are trying to avoid." Now none of these gentlemen site any literary references for the views expressed, so I don't know if these are accepted theories of ornithology or not. However, I found the following reference in "Watching Birds, an Introduction to Ornithology": "The size of various parts of a bird's brain reflects the relative importance of the areas they control. The optic lobes, related to vision, are large." "Birds can distinguish objects much farther away than can humans, and their vision is in fact the most highly developed of any animal." Now, it seems strange to me that a bird, with the most highly developed vision in the animal world, would have a problem "refreshing" its receptors (the same rods and cones that we have), or having them "bleached-out", or distinguishing their own movement from that of an external object. One final note from "Watching Birds, an Introduction to Ornithology": "Most of the area a bird sees is perceived with only one eye... A disadvantage to perceiving an object through only one eye is the difficulty in judging distance, and for this reason you often see a bird cock its head to carefully focus on an object; likewise, the bobbing up and down of the head characteristic of many shorebirds may be an effort to guage distances." Mike
arf@gagme.chi.il.us (jack schmidling) (08/10/90)
Article 1196 (2 more) in rec.birds:
From: mjm@oliven.olivetti.com (Michael Mammoser)
Newsgroups: rec.birds,sci.bio
(SAME) Subject: Re: HEAD JERKING OF WALKING BIRD
> What was it that you thought you were accomplishing?
ARF says:
I can not tell a lie. I grew up with visions of St Francis
and came to realize they were BS so I tried to fool Mother
Nature.
However, there is another complication to factor in. The
kestral was one that I had rehabilitated several years ago.
It broke its leg when it first left the nest. I recovered
it, splinted the leg and hand-raised it. {Right, that is
against the law too.}
So now we have a dove that is alive because I saved it from
a kestral that is alive because is set its broken leg.
But do not forget, that come November, I can shoot the dove
and eat it with impunity.
You figure it out. I quit.
arf
andrewt@cs.su.oz (Andrew Taylor) (08/11/90)
From "The Life of Birds" by Welty: "Doves, gallinaceous birds and rails normally accompany each walking step with a sudden forward jerk of the head. The head then remains fixed in space as the body moves forward until the next step is taken. This permits sharper vision than would otherwise be possible, for a steadily moving head can not see objects - expecially other moving objects - as clearly as can a head fixed in space (Stresemann, 1927-1934). Motion picture analyses by Bangert(1960) of the head and leg movents of the the domestic Chicken, Gallus gallus, showed that the two movements are strictly co-orddibated and in a rhythm of a about 2.2 to 3 cycles per second. If a bird is passively carried foward legs free from the ground, so that its retinal images will shift, the head will bob to and fro, along with perfectly coordinated leg movements. if the stimulus of shifting retinal images is prevented by ground-glass spectacles, the head still swings to and fro whenever the bird walks. The innate nature of both head and leg movements was established with newly hatched chicks reared in compleete darkness." I'd recommend The Life of Birds to anyone interested in a gaining a deeper knowledge about birds. I believe its commonly used as a university textbook. Andrew
mjm@oliven.olivetti.com (Michael Mammoser) (08/14/90)
> In article <63474@oliveb.atc.olivetti.com> mjm@oliven.olivetti.com (Michael Mammoser) writes: > > This difference (parallax) is the way that we make accurate > judgements of the distance that the object is at. Birds with > monocular vision are viewing a distant object with only one eye. > They bob their heads back and forth to shift the position of > their eye in order to provide this parallax. Sounds logical anyway. Well, I found a reference that disputes the idea about distance judgement. It is in "Bird Behavior" by Robert Burton. "Birds other than owls have to judge distances by a number of tricks,... Bobbing the head gives views from different angles and makes objects move in relation to the horizon so their position can be judged." "When pigeons and peacocks walk, they nod their heads to and fro, but this has a fifferent function from head bobbing. They are stabilizing the head, throwing it forward then keeping it steady while the body moves up. With the head steady, the eyes are better able to pick out tiny objects and slight movements." Mike
mjm@oliven.olivetti.com (Michael Mammoser) (08/14/90)
In article <641@gagme.chi.il.us>, arf@gagme.chi.il.us (jack schmidling) writes: > > But do not forget, that come November, I can shoot the dove > and eat it with impunity. Come November, you may be able to shoot the dove and eat it with the PROPER PERMIT. You also may be able to remove the dove or kestrel from its nest and raise them with the PROPER PERMIT. However, you can do neither with impunity. Mike