Many of the field marks that we use to identify species of birds involve the color patterns created by feathers, so it is helpful to understand the basic elements that come together to form these patterns. Despite the seemingly infinite variety of bird coloration, it is limited by some simple facts about feathers. Becoming familiar with these constraints will help a lot as you develop an understanding of the birds’ appearance.
I’ve written in previous columns about how the arrangement of feathers produces and also limits the color patterns of birds (“Streaks and Spots,” December 2014 issue). In this column, I focus on the sizes of different feathers and how that influences color patterns. Generally, feather size changes from smallest and shortest at the front of the bird (around the base of the bill) to largest and longest at the back of the body, disregarding the large and specialized feathers of the wings and tail. Streaks or spots are always smaller toward the front of the bird and larger to the rear because the size of the feathers differs. This change in feather size has a profound impact on color patterns, both the intricacy and the changeability of patterns.
Tiny feathers on the head can each be colored differently to form a very detailed tapestry of color. Each feather might be one solid color, but a pattern is created by arranging many tiny feathers with contrasting colors. And because these feathers are short and stiff, they don’t flex and move, and the pattern always stays the same.
Much larger and longer feathers on the body provide a coarser “template” on which to apply a pattern. Each individual feather might show a single dark shaft streak or a single spot, but relatively few feathers are involved. And because these feathers are long and flexible, their tips can move across other feathers, and the pattern of streaks moves around. Streaks on the flanks can be arranged in three lines, two lines, no lines, a crisscrossing pattern, and more, all on the same individual bird over a short period of time.
This is one of the primary reasons that head patterns are so much more useful for identification. When looking at head patterns, details really matter. The exact shape of pale markings around the eye, the shape of a pale eyebrow, the color and pattern of crown stripes, etc., are all reliable and consistent, never changing as the bird moves around.
Think about feather sizes as you watch birds this season and see what you can learn about how feather size and color pattern are connected.
This article was first published in the November/December 2021 issue of BirdWatching magazine.