Let’s say you’ve just found out something new about a species of bird, a certain turaco that is a very dark cryptic green, in the forests of the Congo. The species hasn’t been studied much, and you’ve discovered that the male birds have a special pigmentation only visible in the ultraviolet spectrum, and this pigment is found in a barred pattern across their undersides, which they display to females and other males in their dense colonies. Based on certain test results, you can positively claim that the pigment is easy and inexpensive to produce, and you’ve also ascertained that the bars of ultravioletly-pigmented feathers are closely correlated with the bird’s growth—that is, older birds have wider bars. But apart from these few facts, you know very little about the turaco species, and your job is to wonder how and why the ultraviolet barring and its display evolved.
