Birds have a very acute sight. Their eyes are better equipped than ours to capture light, even when it is scarce. The density of the visual cells (called cones and rods) that are found in their eye is in fact five times greater than that of the human eye. Furthermore, for each eye, the birds have two or three fovee. We have only one.
The foveas are areas that are found in the retina, in which the receptors are even more numerous: up to a million cones per cm 2 . They probably allow you to recognize moving objects. Nevertheless the birds prefer to avoid the very thick fog, flying higher.
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