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Why do many animals, such as mammals and birds, have white underbellies? (continued)
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Anne Barnfield
London, Ontario, Canada
That many animals and birds have white undersides and coloured backs is probably for the same reason that fish are often paler underneath than on top – to make themselves less visible to predators or prey. Imagine a hawk flying over an animal that is on the ground or on a tree branch. A grey or brown topside would blend in more with the environment and be more difficult to spot. Conversely, an animal with a lighter underside would be less visible against the lightness of the sky when viewed from underneath. In the same way, a predator that was darker on top and paler underneath would also blend in more with their surroundings when moving toward a prey animal.
Derek Bolton
Sydney, Australia
Dark above, lighter below is a near-universal arrangement in animals, most likely to reduce visibility to prey and predator. The transition tends to be sharper in well-lit environments and more gradual in shady ones. There is also an energy cost in producing the pigment melanin, which is part of the reason why human hair whitens with age.
Dyane Silvester
Arnside, Cumbria, UK
I suspect that mammals’ and birds’ white bellies are for camouflage: as potential prey (or predator) on the ground will be looking up at the creature against the relatively pale sky. This is also common in marine creatures.
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