Many birds have white patches in their tails, and the shapes of those white patches can be a very useful identification clue. But they look different from above and from below, and they change dramatically as the tail opens and closes.
Understanding the mechanics of the tail and the arrangement of the tail feathers is the key to understanding the changing appearance of these white patches.
The tail is essentially a fan, with long, straight feathers in pairs left and right. When the tail is open, the feathers fan out to form a wide triangle. When the tail is closed, the feathers stack on top of each other (roughly in left and right stacks); the outermost feathers slide under to form the bottom of each stack, and the central tail feathers are on top.
When the tail is closed (all feathers stacked up) and viewed from the side or from above, we see mainly the central tail feathers and the outer edge of each of the other feathers. When viewed from below, we see entirely the outer tail feathers at the bottom of the stack.
White tail spots are always on the outer tail feathers, and the central tail feathers are always dark. On species with white tail spots, this means that the closed tail viewed from above or from the side appears all dark (the dark central tail feathers) and viewed from below appears partly or entirely white (the outer tail feathers).
Keeping this feather arrangement in mind will help you understand the changing appearance of tail patterns. Watch for it on familiar species to improve your birding skills.
This article was first published in the November/December 2020 issue of BirdWatching magazine. Subscribe now.