Supercilium

The term supercilium is a name for a plumage

Plumage

Plumage refers both to the layer of feathers that cover a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage vary between species and subspecies and can also vary between different age classes, sexes, and season. Within species there can also be a...

 feature present on the heads of many bird species. It is a stripe which starts above the bird's loral area, continuing above the eye, and finishing somewhere towards the rear of the bird's head. It is distinct from the eyestripe which is a line which runs across the lores, and continues behind the eye. Informally, the supercilium is often known as the "eyebrow".

The term supercilium is a name for a plumage

Plumage

Plumage refers both to the layer of feathers that cover a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage vary between species and subspecies and can also vary between different age classes, sexes, and season. Within species there can also be a...

 feature present on the heads of many bird species. It is a stripe which starts above the bird's loral area, continuing above the eye, and finishing somewhere towards the rear of the bird's head. It is distinct from the eyestripe which is a line which runs across the lores, and continues behind the eye. Informally, the supercilium is often known as the "eyebrow". Where a stripe is present only above the lores, and does not continue behind the eye, it is called a supraloral stripe or simply supraloral.

On most species which display a supercilium, it is paler than the adjacent feather tracts.

The colour, shape or other features of the supercilium can be useful in bird identification. For example, one way to tell Dusky

Dusky Warbler

The Dusky Warbler, Phylloscopus fuscatus, is a leaf warbler which breeds in east Asia. This warbler is strongly migratory and winters in southeast Asia. It has a foothold in North America in Alaska, and has also occurred in California...

 and Radde's Warbler

Radde's Warbler

Radde's Warbler, Phylloscopus schwarzi, is a leaf warbler which breeds in Siberia. This warbler is strongly migratory and winters in southeast Asia....

s apart is to look at their supercilium. On Dusky it is sharply demarcated in front of the eye, a bright cream colour here, but becoming duller to the rear, whereas on Radde's, it is loosely-demarcated in front of the eye, buff-orange here and bright to the rear.

A split supercilium is a feature present on some shorebirds (e.g. Broad-billed Sandpiper

Broad-billed Sandpiper

The Broad-billed Sandpiper, Limicola falcinellus, is a small wading bird. It is the only member of the genus Limicola; some have proposed that it should be placed in the genus Erolia with the "stint" sandpipers, but more recent research suggests that it is should rather go into the genus...

). This term is used to describe a plumage pattern where the supercilium has an extra stripe branching off it above the lores, and extending up into the crown.

A supercilium drop is a feature found on some pipits; it is a pale spot on the rear of the ear-coverts which, although separated from the supercilium by an eyestripe, can appear at some angles to be a downward continuation of the supercilium.