Rictal Bristles


Small Green Barbet

I learned the other day that synchronized swimmers don’t shave their legs, at least not to the point of smoothness. Apparently the hair on their legs gives them a sense of where their legs are in the water. Try lightly running your hand along your hairy arm or leg – there clearly is a sense of touch connected with our hirsuteness, as meager as it may be. We also know that cats, mice, dogs, and many other mammals use their whiskers, bristles, vibrissae, or whatever one calls them, to sense their environment by touch. Now, lots of birds have bristles around their jaws and face such as this barbet. These are called rictal bristles because they are located at the rictus, the gape of a bird’s mouth.

For many years it was thought, and logically so I think, that the bristles that surround a bird’s beak served as an insect net or sweep to scoop up insects as the bird foraged through the air. It made some sense. When I started graduate school (back in the Mesozoic) I was looking for a research project and happened to read about rictal bristles; they intrigued me. Exactly how did these bristles work? It seemed to me flycatchers might provide some answers, so  I captured some flycatchers and put them in a large glass-fronted cage. I inserted house flies into the cage one at a time and the birds learned to fly down to capture the insect as it was introduced into the cage near the glass. As the birds swooped down to capture the fly, I filmed them at 400 frames per second, not a big deal today but at that time it was high tech. Remember, movies were shot at 24 or 32 frames per second. So I’d go through a roll of film in about 11 seconds and ended up with a fairly large stack of developed film. (No pixels those days.)

Puerto Rican Nightjar

After spending months filming the birds I edited the movies. Most of the film fell on the cutting room floor, as they say, because the actual insect capture took only a second. But I got plenty of shots that showed me that rictal bristles had nothing to do with prey capture, at least nothing that I could see. The flies were invariably caught in the tips of the flycatchers’ bills, which are hooked at the tip. (If you are interested in reading about what I did, you can access my published research paper: The Role of Avian Rictal Bristles.)


It seems obvious that bristles would serve as insect nets – look at this nightjar, an aerial insect eater. Makes sense, right? But after discovering that Cedar Waxwings, Bald Eagles, Kiwis, and various other birds that typically don’t catch insects mid-air, I wondered what these modified hairs did do. Nobody knows for sure, but the consensus seems to be that rictal bristles have a sensory function, letting the bird know its speed and orientation in the air. The Kiwi doesn’t fly but is a nocturnal forager with very long rictal bristles which the bird probably uses to find food in the soil.


17 thoughts on “Rictal Bristles

  1. Wow Roger, not only very interesting but also another example of why one should always question ones assumptions. Cheers, Peter

  2. PS Other seals – eg elephant seals – have different whiskers used for finding prey by touch, so maybe these correspond to the bristles on kiwis etc

  3. Dear Roger,
    I have spent the last few years working on bristle function in the Caprimulgiformes. My PhD student has done some beautiful histological work on members of the different families so we might be able to provide more evidence regarding their function, at least in this group. We certainly agree with your early work, and that of others, that they dont aid in prey capture but have a sensory role. I recently had a paper on this rejected by AUK. They liked the science but not the writing. Between us, we will hopefully unravel the function of this largely overlooked feature.

    1. Thanks for that interesting information. There was some histological information on rictal bristles and their sensory function in a pair of books on the avian integument by Peter Stettenheim, but I don’t remember exactly what. I would think that the Caprimulgiformes would provide some good information on this subject. Thanks for letting me know.

  4. They are proto-feathers similar to what started sticking out on the very fast moving bi-pedal dinosaurs in the first place. They move lymph both mechanically and electromagnetically, similarly to the mammalian hair. Much oxygenation of the lymph/platelets takes place in the tissues of the avian head, what you call the HALT and becomes “red blood” there, not in the lungs, which are entirely excretory in function in all earthbound creatures who possess them. These tissues are greatly exaggerated on Gallus because it is sedentary/domestic and has evolved thus for ages. A chicken keeps their wattles wet because this tissue oxygenates platelets best when wet, a holdover from reptiles and why human ears are covered with wax. I would imagine a bristle to be covered with tiny scales similar to a human hair. They act as lenses to the core of the hair which is itself something of a nano-tube that heats lymph. Note: if my theory is correct all of western biology is a farce. Just want to put that out there.

  5. The location of the rictal bristles is almost certainly reflective of their innervation by the trigeminal nerve. In mammals, the vibrissae are similarly innervated by the trigeminal nerve, mainly the maxillary branch. The vibrissae of murid rodents are components of the “sinus hair” apparatus, and are used in “active sweeping”. Not necessarily true of all mammals with vibrissae. I don’t know of any evidence of such active sweeping in birds. There is a very large literature on whisker control in mammals, and of their singular representation at all levels, from periphery to brainstem, and then post-synaptically at thalamic and cortical levels. There is no literature on this in birds.

  6. It is possible that Rictal bristles are both for sensory purposes and to impede the flow of air over the eyeball during flight.

  7. For discharge of static electricity build-up during flight. Can’t have all those electricities building up, making the poor little birdie explode in a flash of fire, can we?
    Has anyone ever trimmed them off to see what happens in their absence?

    1. Interesting idea but not likely. If there were any static electricity buildup it would be dissipated by the hundreds of other feathers or feet. I’ve found birds with broken or no bristles who were perfectly healthy.Besides, many flying birds have small or almost absent bristles.

  8. And there is the possibility it’s sensory for protecting the eye from injury, so reflex arc trigeminal with facial and occulomotor nn.

  9. Prehension of a flailing prey insect would certainly risk the eye. Extending proprioceptive sensors from eyelid to the comminsure seems logical.

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