Where is the Supercilium?
If you have been looking through bird guides trying to identify a particular species, you might have come across the term supercilium. In simple terms the supercilium is a stripe that runs from the base of the beak, above the eye and running to somewhere at the back of the bird’s head.
Not found on every bird, the supercilium is also known as the eyebrow and is different to the eyestripe. The eye stripe runs across the lores and runs behind the eye. If the stripe is present only above the lores and doesn’t run behind the eye it’s called a supraloral stripe which is often abbreviated to just a subloral.
To find out more about the supercilium, keep reading.
Table of Contents
What Does The Supercilium Look Like?
The supercilium literally means “above the eyelid” and is a set of feathers that run from the beak of the bird to the back of its head.
On most types of birds that have a supercilium it is lighter than the surrounding feathers. This makes it useful when trying to identify various bird types. Especially because the size, shape and colour can vary from species to species.
One example of this is the dusky warbler which is very similar in appearance to the Radde’s warbler. The dusky warbler’s supercilium is white and narrow at the front becoming broader and more buff coloured towards the rear.
Whereas the Radde’s warbler’s supercilium is more yellowish in colour and broader at the front becoming narrower towards the rear.
The jack snipe has a supercilium that splits above the lores and reconnects behind the eyes.
In essence the supercilium can vary from species to species with some being distinctly different to others while some species don’t have a supercilium at all.
In some cases, the supercilium is the only discernible difference between two species of bird.
Which Birds Have A Supercilium?
There are various birds found in the UK that feature a supercilium including;
- Willow Warbler
- Northern Wheatear
- Spotted Redshank
To name just a few.
What is The Supercilium Used For?
Whilst the supercilium is useful for us as a means of identifying various bird species, birds use the supercilium in displays during courtship as well as for alarm calls to other birds.
Just like human eyebrow movements can convey different messages, so too in the avian world. The movement of the supercilium can be used to send messages of intention, mood and disposition to other members of the same bird family.
These messages can signify aggression, danger, attraction to a female of the species, as well as displays of health and dominance. The supercilium are also used by fledglings to identify their parents in large colonies.
In many bird species, the male’s supercilium is far brighter and ornamental than those of the female. This helps the male to appear more attractive to would be mates.
The development of supercilium can also be attributed to various environmental factors including densely vegetated areas. The colour and size of the supercilium can help other birds of the same species identify visual communications via the movement of the supercilium.
There are even some birds that live in areas which include sandy, thorny or insect laden spots that have developed stiff supercilium feathers to protect the eyes from any foreign bodies. Including sand, thorns or insects.
Plus the overhanging of these eyebrows help shade the eyes from too much glare which helps in many areas of the bird’s life including feeding and general survival.
The supercilium is also useful as a means of blending into the area. This helps to break up the bird’s eye’s outline allowing the bird to blend into the area. This is good to protect the bird from would-be predators as well as allowing them to prey on food without detection.
Frequently Asked Questions
A bird’s eyebrow is called the supercilium. Supercilium literally means “above the eyelid” and is a set of feathers which runs above the back of the bird’s eye to the back of the head.
The supercilium is useful for birdwatchers as it can sometimes be the only way of correctly identifying one species of bird from another.
Birds use their supercilium as a means of communication. For instance, the supercilium can convey aggression, danger, a way to attract a female of the species as well as displays of dominance and health. It is also used by fledglings to identify their parents in large bird colonies.