Supercilium
A stripe above the eye used to identify bird species.
The supercilium is a head marking in certain birds, often called an "eyebrow." This stripe begins at the base of the beak, runs above the eye, and ends toward the back of the head. It differs from an eyestripe, which crosses the lores (the area between the beak and eye) and extends behind the eye. If a stripe appears only above the lores and stops before the eye, it is known as a supraloral stripe. In most birds that have a supercilium, this stripe is lighter in color than the surrounding feathers.
The supercilium’s color, shape, and other details help with bird identification. For instance, the dusky warbler’s supercilium is sharply defined, whitish, and narrow in front of the eye, then widens and becomes more buffy toward the back. In contrast, the similar Radde’s warbler has a diffuse, yellowish supercilium that is broadest in front of the eye and narrows to a whiter tone behind it. Among New World warblers, the northern waterthrush has an evenly buffy eyebrow that stays the same width or narrows slightly behind the eye, while the Louisiana waterthrush shows a bicolored supercilium that widens noticeably behind the eye.
A split supercilium divides above the lores. In some species, like the jack snipe, these divided stripes rejoin behind the eye. In others, such as the broad-billed sandpiper, the stripes remain separate. A supercilium drop is a pale spot on the rear of the ear coverts found in some pipits. Although separated from the supercilium by an eyestripe, this spot can appear at certain angles to be a downward extension of the supercilium.
- Field
- Ornithology
- Known for
- Plumage feature used in bird identification
- Related terms
- Eyestripe, supraloral stripe, supercilium drop
Lore & Background
The supercilium varies in color, shape, and definition across species. For example, the dusky warbler's supercilium is sharply demarcated, whitish, and narrow in front of the eye, becoming broader and more buffy towards the rear, whereas that of the Radde's warbler is diffusely defined, yellowish, and broadest in front of the eye, becoming narrower and more whitish toward the rear. The northern waterthrush has an evenly buffy eyebrow that is either the same width throughout or slightly narrower behind the eye, while the Louisiana waterthrush has a bicoloured supercilium that widens significantly behind the eye.
Reader's Guide
The supercilium is a key field mark for distinguishing similar bird species. In the dusky warbler and Radde's warbler, differences in the supercilium's sharpness, color, and width pattern allow identification. Similarly, the northern waterthrush and Louisiana waterthrush can be told apart by subtle differences in supercilium color and shape. A split supercilium, which divides above the lores, occurs in species such as the jack snipe (where the divided stripes reconnect behind the eye) and the broad-billed sandpiper (where they remain separate). A supercilium drop, a pale spot on the rear of the ear coverts found in some pipits, can appear as a downward continuation of the supercilium at certain angles. These features make the supercilium a valuable tool for ornithologists and birdwatchers.
Did You Know?
- The supercilium is also known as an 'eyebrow' and is distinct from the eyestripe.
- A stripe present only above the lores and not continuing behind the eye is called a supraloral stripe.
- The dusky warbler's supercilium is sharply demarcated and whitish in front of the eye, becoming broader and buffy toward the rear.
- A split supercilium divides above the lores; in the jack snipe the divided stripes reconnect behind the eye.
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