Owls fly almost silently (if they don't use hairspray)
By Maja Mielke
Researchers applied hairspray on feathers to study what makes the flight of some bird species so silent.
A while ago, I found a flight feather of an owl during a hike in a nature reserve here in Antwerp. It was a beautiful, big feather with broad brown bands, and I was thrilled to have found such a treasure. However, there is one thing that I didn’t realize back then. Flight feathers of owls have a very soft, almost furry coating on parts of their upper surface. It feels like velvet (and that’s what it’s called). And researchers have been showing that this velvet is what makes the flight of an owl so extremely quiet!
The velvet on owl feathers is made up of super-thin elongated filaments that extend from the microstructures that help the barbs of the feather stick together (the barbs are the branches that you can pull apart and stick back together in a feather). The velvet covers only parts of the feather (depending on the species, sometimes only some patches), and it’s so soft!
On the owl feather (left) you can see the soft velvet layer that is missing on the hawk feather (right). Photo by Eike Wulfmeyer, CCBY-SA 3.0, via Wikimedia Commons.
Researchers from the Animal Aeroacoustics Lab at the University of California have been studying the function of this velvet for a while already and just published a new study in January 20251.
They showed that the softness of the velvet helps to reduce the noise made by feathers during flapping flight. Specifically, the softness of the velvet functions as a dry lubricant, which reduces the frictional noise of feathers rubbing against each other. To prove that, the researchers sprayed the velvet with hairspray (thereby disabling its softness) and observed that the noise of the sprayed feathers became significantly louder when being rubbed against each other.
They tested flight feathers of 17 different bird species (among them species both with and without velvet), and indeed, the velvet feathers of the barred owl produced the most silent sound of all tested bird species (the loudest being the Andean Condor). On average, velvet feathers were 20.9 dB quieter than species without velvet. That’s roughly the difference in noise level between normal breathing and whispering. For a nocturnal hunter, such a difference in flight noise can be the key to success.
Photo by Elihu Gideon on Unsplash.
Velvet feathers became 7.4 dB louder when coated with hairspray. Feathers without velvet, however, became only 1.7 dB louder with hairspray. Since these feathers didn’t have their own noise-canceling in the first place, the hairspray didn’t make much of a difference.
Although the study has its limitations (feathers were rubbed against each other by hand, which cannot guarantee standardized conditions and not necessarily reproduces the sounds during flapping flight in live birds), this once again supports the hypothesis that velvet improves quieting the sound of feathers during flight in owls.
However, this reduction of frictional noises is only one of several reasons for the silent flight of owls. There are other features contributing as well. For example, their wings and feathers create less turbulence in the air. Also, owls have large wings compared to their body size, which allows them to glide a lot rather than flapping many times while chasing their prey.
If you’d like to see the silent flight of a barn owl in action, I highly recommend having a look at this video from BBC Earth:
Experiment! How Does An Owl Fly So Silently? | Super Powered Owls | BBC