I have heard people say they could tell it was spring because the goldfinches were back. But the goldfinches never go anywhere—they just change their feather colors. It can be hard to believe that the drab little birds of winter are the same as the bright yellow ones with the striking black wing bars in the spring and summer. And, interestingly, the black color doesn’t change, but against the bright yellow body, the black looks much blacker in the spring and summer than it does against the olive drab in the winter.
Geoffrey E. Hill has written a magnificent book for the general reader about how and why birds are colored the way they are. How birds are colored has to do with pigment, chemistry, physics, and diet. Why birds are colored as they are has to do with evolution. Why would painted buntings evolve to have bright, different-colored patches? Wouldn’t that make them more conspicuous to predators? Why would female northern cardinals prefer a bright red male to one that isn’t quite so bright? How do birds tell each other apart? Scientists don’t know all the answers, of course, but there has been a lot of research that tries to answer these and other questions. When Hill was editing a two-volume compendium of current scientific papers about bird coloration, he knew he wanted to share what ornithologists have been learning with the non-scientific community, and he’s done that in this book.
You’ve probably seen a lot of birds at your feeders that are little brown stripy jobs. Some have red on their breasts, head and a little bit on their backsides. These are most likely house finches (around here, in the southeast), though there are other species that fit that description. Male house finches have the red, females don’t. The redder the breast, researchers have found, the more carotenoids in the male’s diet. The better the diet, the redder the breast. Females are attracted to males with redder breasts, i.e., males with healthier diets. Birds that have blue feathers don’t rely on diet for this coloration; different shades of blue come from light reflecting from a certain structural pattern of the feathers. Blacks and grays come from melanin, and browns, rusts and other earthy tones come from other chemicals.
Mate choice is one reason some birds are spectacularly colored. Over millennia, males of some species have gotten prettier and prettier to compete with their fellow males for the attention of females. Often the more spectacularly colored a male is, the more likely he is to find a female willing to pair with him. Most birds have lifelong partners, but there are a lot of extra-pairings going on, and females (of some species) prefer to “cheat” with the more brightly-colored males. Then why would other bird species be drab browns, grays and whites? Camouflage is a good reason for birds to be dull colored. Some birds fare better when they blend in with their surroundings.
This book is full of exciting discoveries told in short chapters. There are sidebars with tidbits of information, notes to birders that offer specific identification tips, and many gorgeous pictures. It’s a National Geographic publication, so the photos are spectacular. Find out what researchers have been learning about these beautiful creatures you see every day.
Check the WRL catalog for National Geographic Bird Coloration.