Why are birds more colorful than mammals?

Mammals evolved from nocturnal animals who did not need color vision. Thus, it made no sense for them to have colored bodies to display.

And even today’s birds, if nocturnal, are generally not very colorful compared to those who are diurnal.

When dinosaurs disappeared, mammals started to thrive and to diversify. The ones who adopted a diurnal lifestyle also evolved color vision, which was initially used primarily to identify ripe plants and fruits (whose bright colors attract frugivores and insects).

With the ability to recognize colors, colorful coats began to spread in mammals as well. And primates, feeding largely on ripe fruits, are among the mammals with the best color vision. That’s also mirrored by the vibrant colors of some of their coats.

Most other mammals, on the other hand, have colors that typically range from white (common in the arctic regions) to gray, black, and to different shades of red (orange, red, brown). Of course, there are exceptions, like this Indian squirrel.