Eyes Judge Distance Without Head Movement

close up of a green and brown lizard with eyes pointing different direction against a blurry background

Biological Strategy

Chameleons

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Sense Light (Visible Spectrum) From the Environment

Living systems constantly receive signals from their environment that help them survive. Light (in the visible spectrum) can come from other living systems (such as fireflies) or from non-living sources (such as the sun). Survival often depends on sensing and responding to challenges like low light conditions or light that has been altered in some way. Because basic survival is at stake, living systems must excel at meeting those challenges. A well-known phenomenon is how water bends light. A stork trying to catch a fish underwater can compensate for this bending effect so that when it strikes at the fish, it has a good chance of catching it.

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Reptiles

Class Reptilia (“creeping”): Lizards, crocodiles, turtles, snakes

Reptiles retain some of the key characteristics that first enabled vertebrates to live permanently on land. They have dry skin covered in scales made of keratin that help prevent water loss. (Amphibians still need to stick close to water to keep their skin moist.) Many reptiles reproduce by laying eggs that are watertight and have a yolk, so eggs can develop on land while staying moist and nourished. Reptiles are also ectotherms, meaning they don’t produce their own body heat. This means they burn through energy much more slowly than “warm blooded” creatures of the same size. It also means that they need to keep warm to keep active, which is why you might see them spending a seemingly inordinate amount of time simply basking in the sun.

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The cornea of a chameleon, rather than the lens, focuses incoming light to create an image, allowing chameleons to judge distance moving only their eyes.

“In most higher animals, the eyes have a lens for focusing incoming light onto the retina to create an image. The chameleon, however, uses the cornea for this purpose, and therefore avoids drawing attention to itself when trying to see how far away a potential prey is. Most other animals judge distances by moving their heads from side to side, causing closer objects to appear to move more quickly than distant ones. This is known as the parallax effect. But the chameleon can achieve this effect by only moving its eyes. This ability means that the chameleon does not attract the attention of predators when it looks around.” (Shuker 2001:13)

Last Updated August 18, 2016

References

Book

The Hidden Powers of Animals: Uncovering the Secrets of Nature

26/02/2021 | Dr. Karl P. N. Shuker

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