If you look closely, you may notice that some birds seem to have whiskers like a cat. In fact, these are not whiskers, but feathers. But why do some birds have such odd looking feathers around their mouths or eyes?
The Purpose of Feathers
Feathers are undoubtedly one of birds’ most defining characteristics. But not all feathers serve the same purpose.
All feathers take on the same basic shape—a central branch (called a rachis) with barbs extending off of it. Feathers take on a variety of roles. Some, like down, help birds stay warm and dry. Others, like remiges (wing feathers), evolved so birds could fly.
And of course, some feathers, like the peacock’s tail feathers, serve the purpose of procuring mates.
But another type of feather—rictal bristles remains a bit of a scientific mystery.
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Rictal bristles of a Small Green Barbet / L. Shyamal Creative Commons
What Are Rictal Bristles?
Rictal bristles are simple feathers, more or less comprised of only the rachis—the central stem of the feather. These feathers are primarily found on the face of birds, mostly around the eyes and mouth opening (the rictus).
Originally, scientists assumed that these small feathers helped insect-eating birds catch their prey more easily. The rictal bristles, they surmised, served as a net to sweep the insects into their beaks.
But a couple of scientific studies cast doubt on this theory. Noticing that species such as ravens and crow also have rictal bristles, one scientist observed and filmed the feeding behavior of flycatchers. He noticed that rather than helping birds catch flies, the insects instead got stuck in the bristles.
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Willow Flycatcher / Shutterstock
A second study in the 1980s confirmed the previous findings. These scientists compared the ability of willow flycatchers to catch flies after their rictal bristles had been removed to those flycatchers who still had them. Both groups captured flies at the same rate. The rictal bristles appeared to have no affect on a bird’s ability to catch insects mid-air.
The same study also looked at the purpose of bristles around birds’ eyes. The same scientists put flycatchers through wind tunnels. They attached adhesive discs to the birds’ eyes, and then tallied the number of particles which stuck to the discs after the birds flew through the wind tunnel.
Afterwards, they removed the bristles around one of each of the bird’s eyes and sent them through again. Eyes without bristles had accumulated a significantly higher number of particles.
These researchers concluded that bristles around the eyes might serve the purpose of keeping dust and dirt out of birds’ eyes while they are flying.
But while that conclusion helped explain why some birds have bristles around their eyes, the question of why birds have them around their beak remains unanswered.
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Common Raven with rictal bristles / Shutterstock
Scientists think these bristles may act similar to other animals’ whiskers—serving the purpose of communicating touch. The bristles may help birds understand their speed and orientation in the air. For non-avian birds, the bristles may help them forage for insects on the ground.
But there is no certainty yet.
So next time you are out with your binoculars, see if you can find these thin, hair-like feathers around birds’ beaks. Maybe one day we will have a better idea of how birds use them.
