Table 1.

Mechanisms of color evolution by natural selection, adapted from [19] for animals at large, and Bortolotti [18], who specifically referred to birds. Four broad categories are recognized, although several mechanisms may combine to explain general coloration and specific markings in multi-colored species. Conspicuous colorations mainly resulting from sexual selection or some specific types of intraspecific communication (e.g., marks for species recognition, for gender and/or age recognition, or parent–offspring visual signaling) are not included.

Protection	Ultraviolet (UV)-protection. UV light is damaging to biological tissues. Abrasion-resistance. Sand and dust transported in the wind damages fur, feathers, and skin. Thermoregulation. Dark colors absorb more radiant energy than light colors.
Concealment	Crypsis. Blending in the environment by coloration and pattern. Countershading. Darker color on top compared to a lighter ventral area. Disruptive coloration. Irregular color patches to disrupt the shape of an animal in a variable environment.
Advertising	Unprofitable prey. Conspicuous colors in prey inform potential predators the prey is hard to get or distasteful. Allurement to prey. For instance, the red crest of kingbirds (Tyrannus tyrannus) attracting the bees they eat. Pursuit deterrence. Warning the presence of predators to conspecifics (e.g., white rumps or tails). Cohesion and coordination of the group. Black or white marks in flocking or bunching animal species, such as shorebirds, savannah gazelles, or fish schools. Startle or flash markings. Sudden appearance of conspicuous color patches in cryptic individuals to confuse predators and gain time to escape.
Deception	Resemblance to objects. This particular form of crypsis takes advantage of behavioural adaptations, such as slow motion in sloths, swaying movements in stick insects, and resting owls and frogmouths resembling tree bark or broken branches. False eyes (ocelli) or false faces. As in the wings of some butterflies or the nape of small owls and falcons. Directive marks. Intimidating markings, such as bright-colored irides, to scare off enemies or to obtain prey. Mimicry. Animals resembling others of a different species. The mimic is generally less poisonous or less powerful than the model.