Many families of land vertebrates have average eye darkness near the midrange between yellow and black--in my terms that is red or light brown. Of the 88 large families, the eight families closest to the midrange are as follows: Bowerbirds, Barbets, Toucans, Ducks, Vireos, Old World Monkeys, White-eyes, and Auks.
In contrast to the families at either end of the scale on eye darkness, these families are not so carnivorous and not skilled predators in the land/air environment. Auks are carnivorous, but like penguins they chase and catch fish underwater. Vireos and white-eyes (the name refers to a ring of feathers) glean immobile insects and take some plant matter. The other five families include much vegetation (e.g. fruit) in their diets.
In terms of feeding behavior, there is not much overlap among the three different eye darkness groups that have been considered. Because insects are eaten by all three groups, consider how they are obtained. Among the lightest-eyed families, frogs wait for mobile insects to come near. At the midrange, vireos and white-eyes glean relatively immobile insects. At the dark-eyed end of the scale, swifts, swallows and nightjars catch mobile insects in-the-open and on-the-wing.
Some of the families of animals that are considered most clever or crafty have average eye darkness near the midrange. That includes monkeys, bowerbirds and crows.
June 16, 2006
Midrange Eye Darkness
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