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 Post subject: Re: Bird Quizz (RV)
Unread postPosted: Wed Oct 23, 2013 2:42 pm 
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I still disagree with your source. According to the UN, the world's human population stood at 6,5 billion during 1995.

But this is not something that warrants endless debate. We all agree that the red-billed quelea is the most numerous wild bird in the world.

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 Post subject: Re: Bird Quizz (RV)
Unread postPosted: Thu Oct 24, 2013 6:23 am 
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Rooies I was afraid there were more birds, I didn't think of them. I was thinking about the barbets so you are it :thumbs_up:

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 Post subject: Re: Bird Quizz (RV)
Unread postPosted: Mon Oct 28, 2013 12:43 pm 
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[b]Birds can see better that humans, that's a fact. What part of a bird's eye is different than ours?

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 Post subject: Re: Bird Quizz (RV)
Unread postPosted: Mon Oct 28, 2013 12:51 pm 
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They can see ultraviolet and humans can't. :|

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 Post subject: Re: Bird Quizz (RV)
Unread postPosted: Mon Oct 28, 2013 3:26 pm 
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Philip1, this has not yet been proved. According to the experts, birds may probably sense ultaviolet light and may use this ability in the same way as nectar-feeding insets to detect ultraviolet 'nectar guides' on flowers. My question has something to do with the construction of the eyes.

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 Post subject: Re: Bird Quizz (RV)
Unread postPosted: Mon Oct 28, 2013 3:52 pm 
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:hmz: Rooies, let us try this one: Bird retinas, in contrast to humans, contain no blood vessels. This prevents light scattering and thus provides birds with greater visual acuity than humans.

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 Post subject: Re: Bird Quizz (RV)
Unread postPosted: Mon Oct 28, 2013 8:18 pm 
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I say lets got with Philips second answer as I'm no eye doctor but it does sound kind of spot on :tongue:

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 Post subject: Re: Bird Quizz (RV)
Unread postPosted: Tue Oct 29, 2013 11:49 am 
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In birds the lens is more flattened as opposed to spherical in the human eye. It is also placed comparatively further from the retina which gives it a longer focal length. Longer focal length produces images that appear brighter on the retina as the large pupil and curved cornea admit plenty of light.

Birds also have a very high density of photo receptor cells which allows them very acute vision.

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 Post subject: Re: Bird Quizz (RV)
Unread postPosted: Tue Oct 29, 2013 2:42 pm 
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An answer tomorrow.

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 Post subject: Re: Bird Quizz (RV)
Unread postPosted: Tue Oct 29, 2013 3:31 pm 
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Why do birds see better than humans?

1) Both birds and humans have photoreceptive 'cones' in the retina located at the back of the eye. These cones allow us to see color light. The human eye contains 10,000 cones per square millimeter. Songbirds, for example, have up to 12 times this amount or 120,000 cones per square millimeter.

2) In humans, these photoreceptive cones consist of three types. Each cone is sensitive to red, green, or blue light. This is called trichromatic color vision. Birds have an extra cone for tetrachromatic color vision. This extra cone expands the visible light spectrum, allowing birds to see ultraviolet frequencies.

3) During low-light conditions, both humans and birds rely on photoreceptive ‘cell rods’ in the retina. The human eye has 200,000 cell rods per square millimeter. Some birds, such as owls, have up to 1,000,000 cell rods per square millimeter.

4) Bird eyes, on average, account for 15% of the mass of the bird’s entire head. Human eyes, by contrast, account for less than 2% of the head.

5) Bird retinas, in contrast to humans, contain no blood vessels. This prevents light scattering and thus provides birds with greater visual acuity than humans.
:?

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 Post subject: Re: Bird Quizz (RV)
Unread postPosted: Tue Oct 29, 2013 3:57 pm 
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Philip, you are the first one with a correct answer. Interesting facts about bird's eyes are inter alia,
1 Bird's eyes are proportionally much larger that those of mammals.
2 Birds with laterally positioned eyes, like doves have a 300 degree field of view.
3 The shape of the mammalian eye is spherical, so only a small part of the image falling on the retina is in focus. The problem is akin to trying to project an image from a slide projector on to a strongly concave screen. A bird's eye in contrast is flattened at the back on which the entire image is in focus.
4 Spare a thougt for the cormorants and kingfishers. As you move from air to water, refraction increases by some 20 diopters. We would normally wear glasses to correct for a deficiency of one diopter and the glasses you need to correct for 20 diopters would be so thick you would probably need a neck brace to wear them.

There are more to tell, but I will rest with the above.

Over to you Philip1

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Last edited by Rooies on Tue Oct 29, 2013 4:41 pm, edited 1 time in total.

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 Post subject: Re: Bird Quizz (RV)
Unread postPosted: Tue Oct 29, 2013 4:31 pm 
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Phew.....will be back. :think:

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 Post subject: Re: Bird Quizz (RV)
Unread postPosted: Wed Oct 30, 2013 3:07 am 
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Very interesting, thanks Rooies and Philip. :clap: :clap: :clap:

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 Post subject: Re: Bird Quizz (RV)
Unread postPosted: Wed Oct 30, 2013 9:48 am 
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Feathers of this bird break up into powder. What is the name of this bird?
A bit of info with your answer, please.
:wink:

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 Post subject: Re: Bird Quizz (RV)
Unread postPosted: Wed Oct 30, 2013 10:52 am 
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Well done Philip1 now I know why they say "A birds eye view"

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