The supercilium is a
plumage
Plumage () is a layer of feathers that covers a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage differ between species and subspecies and may vary with age classes. Within species, there can b ...
feature found on the heads of some
bird
Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...
species. It is a stripe which runs from the base of the bird's
beak
The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for pecking, grasping, and holding (in probing for food, eating, manipulating and ...
above its eye, finishing somewhere towards the rear of the bird's head.
[Dunn and Alderfer (2006), p. 10] Also known as an "eyebrow",
it is distinct from the
eyestripe, which is a line that runs across the
lores, and continues behind the eye. 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, the supercilium of the
dusky warbler, an
Old World warbler
The Old World warblers are a large group of birds formerly grouped together in the bird family Sylviidae. They are not closely related to the New World warblers. The family held over 400 species in over 70 genera, and were the source of much taxo ...
species, can be used to distinguish it from the very similar
Radde's warbler. 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 supercilium of the
northern waterthrush, a
New World warbler, differs subtly from that of the closely related (and similarly plumaged)
Louisiana waterthrush. The Louisiana has a bicoloured supercilium which widens significantly behind the eye, while the northern has an evenly buffy eyebrow which is either the same width throughout or slightly narrower behind the eye.
A split supercilium divides above the lores. In some species, such as the
jack snipe, the divided stripes reconnect again behind the eye. In others, such as the
broad-billed sandpiper, the divided stripes remain separate.
A supercilium drop is a feature found on some
pipits;
it is a pale spot on the rear of the which, although separated from the supercilium by an eyestripe, can appear at some angles to be a downward continuation of the supercilium.
Gallery
File:Wilsonia canadensis.jpg, The Canada warbler shows a yellow supraloral.
File:Limicola falcinellus Taiwan cropped.jpg, The broad-billed sandpiper has a split supercilium...
File:Lymnocryptes minimus (Marek Szczepanek).jpg, ...as does the jack snipe.
File:Olive-backed Pipit- Kolkata I IMG 9872.jpg, The olive-backed pipit has a supercilium drop.
References
Notes
Sources
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{{Feather-tracts
Bird anatomy
Feathers