Some birds—the ruby-throated hummingbird, the common grackle—have iridescent contour feathers covering certain parts of their bodies. “Iridescence is typically caused by the structure of the feathers,” says Mark Conboy, the program manager with Birds Canada at the Long Point Bird Observatory in Port Rowan, Ont. “That is to say, how the light hits the feathers and interacts with the microscopic structure of the feather parts determines what colour you can see.” Spot a hummingbird from the right angle, and you can’t miss the red “gorget.” In a different light, that ruby throat just looks like, well, a throat.
“Feathers are inherently waterproof because of their structure,” says Mark Peck of the Royal Ontario Museum. Feathers have interlocking “barbules” (barbed branches) that help to trap air and repel water. Many bird species also have the ability to make themselves even more waterproof thanks to an oil-secreting gland on the rump. Birds “preen” regularly, distributing the waxy oil over their bodies. Research shows that ducks and other aquatic birds have larger preen glands, and, therefore, more oil; they need to waterproof themselves more frequently.
Fancy tails—in cottage country think male wild turkeys or ruffed grouse—are likely the result of “runaway sexual selection,” says Conboy. Over evolutionary time, certain traits become exaggerated and elaborate. “These traits, despite making males more conspicuous, are more advantageous because they amount to increased reproductive success,” explains Conboy. “In these species, females prefer to breed with the fanciest males, thus driving an ever-increasing race towards ever-increasing fanciness.” An extreme example? The male Indian peafowl—a.k.a. the peacock.
Birds can thank natural selection for the drab feathers that help them camouflage—either to increase their success at hunting, as in the case of the American bittern, or to increase their success at hiding, as with the Eastern whippoorwill or the ovenbird. In those cases, “camo for survival trumps any sexual selection that may drive the evolution of fancy colours,” says Conboy. With no bling to flash, dull-coloured birds use elaborate songs to compensate.
Crests are for communication; birds can raise or lower their crests to display aggression, excitement, or submission. “Crests are common in certain groups of birds, like woodpeckers, jays, and owls,” says Peck. Crest feathers could also “represent a signal of health and quality to other birds,” says Conboy. “Crests can be attacked by mites and other parasites.” This is still a form of communication: a female bird may avoid mating with a male with a ratty, bug-filled crest. (Wouldn’t you?)