Head patterns
Why it pays to look for the gape line first when studying birds’ head patterns
Contributed by David Allen Sibley
Published: December 28, 2009
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Art by David Allen Sibley  Art by David Allen Sibley
One of the best starting points for studying head patterns is the “corner of the mouth” — the point formed at the rearward projection of the gape below the eye. From that point, it is easy to trace a line back below the eye, separating the cheeks above (the auriculars) from the lower jaw below (malar).
I have emphasized the line in the five illustrations above. It curves to follow the concentric rings of feathers below the eye, then turns to follow the edge of the cheeks back and down. The rear border of the cheeks then curves up to meet the eye-line, but here we’re going to focus on the lower border. In most species of birds, this boundary between feather groups also corresponds to a contrast in colors.
On Black-capped Chickadee (and all other chickadees), the cheeks are all white and the lower jaw feathers are all black. On Song and White-throated Sparrows, the lower edges of the cheeks are dark while the lower jaw feathers are pale.
Many sparrows show the result — a dark stripe along the lower edge of the cheeks. It originates just above the corner of the mouth and runs back just above the lower jaw. It is in the position where we would expect to see a mustache if birds had mustaches, and it is commonly called a mustachial stripe. On the Song Sparrow, it is bold and dark, and it becomes broader behind the eye. The stripe on the White-throated Sparrow is shorter and less conspicuous.
On Downy Woodpecker (like most other woodpeckers), the mustachial stripe is white while feathers along the lower jaw are mostly dark. The feather boundary extending back from the gape still corresponds to a change in color pattern, but the dark and light colors are reversed from most birds.
Blue Jay has relatively uniform pale whitish cheeks and throat, but the boundary between these feather groups is still conspicuous at close range, and the black “collar” follows the rear border of the cheeks.
There are plenty of small variations and exceptions to these rules, but feather groups are still the best way to understand head patterns. And looking for the “gape line” is one of the best and easiest ways to get yourself on firm footing as you work out the head pattern of any bird.
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David Allen Sibley is the author of The Sibley Guide to Trees, The
Sibley Guide to Birds, Sibley’s Birding Basics, and Sibley guides to
birds of eastern and western North America.
Read more by David Allen Sibley.
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