Our human interface with reality

The funky chickens

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Less fun but slightly more informative:

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Why they do this?, surely not just for our entertainment:

In order to spot potential food that is moving within a stationary background, the chickens must stabilise their eyes in space. Then the only thing that moves within the image falling on their retinas, is the moving target (e.g. a wriggling worm).

Their brains are unable to compute what is happening from a moving frame of reference. They cannot calculate the effect of a moving point of view on a stationary scene to detect movement within the scene (e.g. a wriggling worm), so they stabilise their head (more specifically their eyes). As explained in “Bottleneck”, this enables them to detect movement, using the inherent fading property of the eye, rather than by intensive cerebral processing.

Video of a Kestrel hovering and keeping its eyes fixed in space

These videos are relevant to the section: –  Evolution of the Seeing Eye in Chapter 2 – Sense and sense ability, in the book: Bottleneck – our human interface with reality

5 comments on “Stabilisation of eyes

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Paul Kirkby on January 9, 2014 8:37 pm

A very nice piece of physiology. Is your explanation proven Richard, i.e. is it tested against alternatives. You say the chicken’s brain is too small to deal with moving background but something like a goshawk flying through trees as on recent spring watches has incredible ability to see prey against rapidly moving background. I guess birds of prey have binocular forward vision whereas the chicken has eyes in the side of its head. The chicken is indeed looking for tiny movements . I always wondered why a chicken when it walks moves its head back and forward, maybe the important be is the stationary bit after every step.??

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Richard Epworth on January 9, 2014 8:53 pm

Good point. The chicken’s brain is probably large enough to perform the computational process, but it’s mental powers are addressed towards catching worms etc.. If you see one fly, it obviously isn’t optimised for flying. This behaviour is much more common with smaller birds, where you rarely observe any smooth head motion. Compare the movement of a swan with a blackbird.
If you watch a chicken walk forwards, its head is stationary (in space) most of the time, interspersed with brief forward jerks, while using their neck to facilitate smooth forward motion of their body.