Friday, January 25, 2013

Weird Eyes



Starlings aren't as common as they used to be but we've had quite a few in the garden during the present spell of cold weather. Today I noticed something odd about their eyes that I've never seen before. Above is a starling in wary mode, with its beady eyes looking all around for danger.


Here's a starling trying to feed with that rather strange technique that they use, with their beaks gaping then closing. Take a close look at where its eye is now - almost in its mouth and almost under the upper mandible.



































When a starling switches from wary to feeding mode and it opens its beak wide the tension in the flesh on either side of the gape pulls the eyes forward, so that they are almost on the edge of the mouth and focused with binocular vision on the food source that it's pecking at. Imagine how their focus must flicker between near and far, and their field of view must vary between narrow and broad, every time they open and close their beak and their eyes move backwards and forwards accordingly. 

For a human comparison, it would be somewhat akin to oscillating between reading from your computer screen with both eyes, and then focusing independently with each eye on the walls on either side of the room, then back to looking at the computer screen again, every second or so.

12 comments:

  1. Fantastic photos Phil. I had never noticed in starlings, but I think herons have also that ability to turn their eyes completely forward or sideways

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  2. I'll have to have a closer look.

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  3. Utterly amazing post Phil. I'd always been curious about the strange feeding action of starlings, but never noticed the moving eyes, or even heard of this! You even had me checking that the date wasn't April 1st!

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  4. Hm...interesting.

    And I know where all your starlings are: they are here in the US! Horribly invasive, they are, and huge flocks of them scour the countryside, pushing out our native cavity nesters. Want 'em back? I'll see if I can't shove a few thousand into a shipping container and send it your way! :)

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  5. Fascinating Phil.
    Something I never knew. Thanks.

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  6. Thanks for detailing something I had never noticed about their eyes. They do have a strange way of feeding with that wide open beak, presumably to put the eyes in the right position to see the food.

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  7. I think you're right Africa - they must need good binocular vision to catch fish. One of the things that interests me about the way heron's fish is how they learn to cope with refraction - they must miss a lot of catches when they are juveniles, until they learn to compensate.....

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  8. Hi Adrian, I'd never have noticed without the lucky shot of the bird with its beak open ...

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  9. It amazed me too Richard .......it must make them very vulnerable when they've got their head down, feeding. No wonder they are such jumpy birds...

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  10. Sorry about that Ellen - I seem to remember they are are descendants of a few that were release in Central Park, NY. Still, you gave us grey squirrels, so I guess we're even ....

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  11. Amazing what photos can reveal, isn't it Keith....?

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  12. I've often wondered why they feed like that John...

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