David Sibley: How markings on feathers make spots and streaks on birds

Dark markings that reach the tip of each feather create the streaks seen on many birds, including sparrows. Art by David Sibley.

Birds’ incredible range of color patterns can be useful for identification, but the diversity can also be overwhelming.

The key to deciphering color patterns is understanding a few basic facts about feathers. First, they grow in organized rows, always out from the body and curving back toward the tail. Second, each feather overlaps the one behind it to form a smooth outer contour, like shingles. All we normally see on a bird are the tips of its feathers.

The organization of feathers is so standardized that all songbirds, from crows to swallows to warblers, have the same arrangement. You can recognize the same groups of feathers, even the same number of rows of feathers, in any bird species.

Given this, it follows that the diversity that we see in birds’ color patterns is the result of markings on the feathers, not differences in the number or arrangement of feathers.

When the dark markings do not reach the feather tip, the result is spots, seen on thrushes. Art by David Sibley.

Besides differences in color, in some species, the shape and length of certain feathers are modified. The crown feathers that form the crests of jays, for example, are extra long, but they are the same feathers that all songbirds have; only their shape is different.

Two common patterns — streaks and spots — provide a good starting point for studying the building blocks of color patterns. The difference between the patterns is simply the placement of a dark marking on each feather.

As you can see in the idealized illustrations above, streaks are formed by markings that extend to the tip of each feather. As the feathers overlap, the marking on one feather connects to the marking on the feather behind it. A pattern of spots is formed by markings that do not reach the tip. As the feathers overlap, each spot is separated from the feather behind it by the upper feather’s pale margin.

Look for this when you have an opportunity to study a bird at close range. It can be enlightening to see how simple markings come together to create elaborate patterns.

 

This article from David Sibley’s “ID Toolkit” column appeared in the November/December 2014 issue of BirdWatching.

 

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David Sibley

David Sibley

David Sibley writes the column “ID Toolkit” in every issue of BirdWatching. He published the Sibley Guide to Birds in 2000, the Sibley Guide to Bird Life and Behavior in 2001, and Sibley’s Birding Basics in 2002. He is also the author of the Sibley Guide to Trees (2009), the Sibley Guide to Birds-Second Edition (2014), and guides to birds of eastern and western North America (2016). He is the recipient of the American Birding Association’s Roger Tory Peterson Award for lifetime achievement in promoting the cause of birding and a recognition award from the National Wildlife Refuge System for his support of bird conservation.

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