This image shows one of those unique adaptations of owls that I seldom see in my photos. I photographed this juvenile Burrowing Owl just over two weeks ago after it took off from its fence post perch in Box Elder County, Utah.
1/3200, f/7.1, ISO 640, Canon 7D Mark II, Canon EF500mm f/4L IS II USM +1.4 tc, not baited, set up or called in
The crisp flight feathers of most birds make a very noticeable gushing noise as they pass through the air, as anyone who has been close to a bird in flight as it flaps its wings is well aware. This would be a distinct and obvious disadvantage for nocturnal hunters like owls who hunt by stealth at night. But one edge of most owl flight feathers is fimbriate (fringe-like) rather than “crisp” (imagine the fringe on the edge of a scarf). This fringe breaks down the air turbulence into small groups called micro-turbulences that effectively muffle the sound produced as air rushes over the wing surface and allows owls to fly silently. One theory suggests that the fringing actually transforms the sound energy to a higher frequency that most critters, including humans and prey, cannot hear. Silent flight allows owls to use their own hearing to stealthily locate prey at night.
The position of the wings and the relative sharpness of their tips in this image allow us to see the fringing on the tips of at least four of the flight feathers of the right wing. I’m sure that many of my readers are well aware of this characteristic of owls but I thought it was interesting to see the fringing in a wild bird in flight.
The effectiveness of the fringing is dramatic and education birds are often used to demonstrate that fact to the audience. Typically the educator first holds a hawk or falcon on the fist as the bird is raised and lowered causing it to flap its wings. The noise produced by the wings is loud and can be distinctly heard some distance away. Then the very same thing is done with an owl and when it flaps its wings in response there is virtually no sound produced.
Folks who see this demonstration are usually quite impressed by the contrast. When it was done for my Zoology and Utah Wildlife students when I was teaching it definitely left an impression.
Here’s a link to an excellent video clip that demonstrates silent flight in a Barn Owl if you’re interested.
Ron
Note: I have a question. Multiple internet sources refer to the fringing as being on the “leading edge” of the primary wing feathers. But this image and other experience I’ve had with owl feathers suggest to me that the fringing is instead on the “trailing edge” where most of the air resistance is. I can be a little dense at times (especially after a long night with little sleep because of extremely annoying fireworks in my neighborhood) so I’d appreciate some enlightenment on the subject. What am I missing?…
Great comments here, I learned a few things myself.
Barn Owls must be the champions at silent hunting. My wife had one hover a few feet overhead, flapping its wings quite strongly, yet utterly silent… a truly magical experience.
I had the opposite effect once – a Merlin went by in one of their trademark high-speed glides, only a few feet away, and it sounded like someone tearing a giant sheet of paper. Any faster and it might have produced a sonic boom!
Great shots you have here, Ron.That is a great study in the video, enjoyed watching the smiles on the people, too.I have watched a Barred owl take off in front of me about 10 feet away and it was silent.
I just know that’s an amazing picture. 😀
Fantastic flight shot Ron!
Charlotte
Education, beauty and delight.
What a wonderful start to my day.
Thank you Ron, and thank you to so many knowledgeable people shining light into the dark patches in my skull.
It’s the other knowledgeable people that deserve most of the credit here, EC. I too am indebted to them.
For a real boggle, look at a Great-horned Owl flight feather under strong magnification. What is revealed is that the surface of the feather is like velvet or fur, covered with tiny hairy bits that stand up. They are totally unlike the smooth surface of other feathers. Yes, the edges are fringed, but the real difference is much greater.
This is surely a bigger subject than I initially thought it was, Mikal. I think I learn more from my own posts than anyone else does…
Ron – I’ve emailed you a photo of a barn owl feather that shows the comb-like serrated leading edge, and the less tightly woven trailing edge that leads to the fringe effect. Basically, I ditto what my friend Dan Gleason has said – it’s the combination of the extra softness (less tightly woven) of the flight feathers, the leading edge serrations, and the velvety texture overall that contributes to the silent flight that nocturnal owls need to hunt by hearing. When I’ve got a falcon on the glove, and she flaps – the slap of the feathers on my face actually can sting, they are so rigid and stiff (redundant, I know!) When an owls does it, it’s like a caress.
Thank you, Louise.
There’s sure a lot of confusing info out there about this. Confusing for me anyway but I’m getting there…
Now that you probably have more info than you where expecting my I add one more. I was surprised I could still find it on the internet, I ran into it many years ago when looking for specific information on owl feathers. http://www.biomedcentral.com/content/pdf/1742-9994-4-23.pdf
Thanks, April.
Now I’m REALLY confused. This paper says the fringes are on the trailing edge and that they’re on each flight feather.
“For the owl, the leading edge comb-like serrations, the
trailing edge fringes on each feather”
Some of the feather photos were very helpful in my understanding of the difference between serrations and fringes.
Maybe we could minimize confusion if we found different terms for these structures. Some authors use fringe to refer only to the stiffened barbs on the outer vane of the leading primary forming this comb-like feature. The wider, trailing vane is soft (in owls) and does not form a smooth edge and so it is also sometimes referred to as a fringe. We may need more clarity about which “fringe” we are referring to.
An interesting aside: The outer vane of the leading primary on a Northern Rough-winged Swallow has stiffened barbs forming a comb-like structure superficially resembling that of owls. It is his feature that gives it its name. The finer details of its morphology differs between male and female swallow. In owls, everyone believes that this is the first thing to help break up the air flow over the wing. In Rough-winged Swallows, which otherwise have smooth, stiff feathers, we have no idea how this feature is used or why i may have evolved. It is not found on other swallows. Always more questions to ask, which makes the study of nature so much fun.
Dan, that first paragraph above was extremely helpful in clearing up much of my confusion. Thanks very much.
And I always wondered about the origin of the common name of the Northern Rough-winged Swallow.
Ron,
The “fringe” that you see on the trailing edge is due to the softness and openness of the feathers, not stiff as in other raptors. But the fringe that is being referred to in reference to owl feathers is the outermost or forward vane of the
outermost primary. In all birds the vanes of the primaries are asymmetrical and the forwardmost, or leading edge of each is the narrowest. in the outermost primary of owls this is a comblike structure and this is the fringe being referred to..
This does help break up the air before it goes over the top of the feather, but it alone does not produce silent flight. In fact, if this fringe is cut off, the owl still flies silently. In most other birds the smoothness and relative rigidity of the wing’s upper surface allows a smooth and efficient flow of air and produces noise. The top surface of an owl’s wing is very soft and the barbs can slide accross each other or flick up slightly into the air flowing over the wing. This creates a small area of turbulence that breaks up the airstream and results in silent flight.
I think that there is often a misunderstanding about why an owl has silent flight. It is not to prevent prey from hearing the owl coming. Many diurnal raptors would have the same problem, especially something like a harrier hunting low over the ground. More than other birds, owls are very dependent on locating their prey by sound and have very specialized ears for this purpose. By having silent slight the owl can concentrate on the sounds of the prey (a mouse rustling dry blades of grass, etc,) without any interference of sounds coming from its own wings.
But there is a price to pay for silent flight. It is much less effecient. Owls with silent flight are not long-distance migrants. And not all owls fly silently. Most day-hunting owls have some wing noise and the one North American owl that does make a longer migtation, the Flammmulated Owl, hunts visually and does not have silent flight.
Thanks, Dan – you’ve provided some very interesting and helpful information, some of which I’ve seen before and some I haven’t. But now I’m really confused…
“in the outermost primary of owls this is a comblike structure and this is the fringe being referred to” – so are you saying that the fringe is found only on the “outermost primary” and not on the other primaries?
Sorry if I wasn’t clear. The leading vane on the very outermost primary (one feather per wing) is the one that is modified into a comb-like structure or fringe. This is the part of the wing hitting the air first as the wing moves forward and down. This begins to break up the air flowing over the top of the wing. The other primaries will lack this modification.
You were probably clear, it’s just that my interpretive filter needs occasional assistance…
Thanks, Dan. I think I’m starting to get the big picture now.
Very interesting shot…those feather edges almost look serrated as much as fringed…Have you ever found a feather to check which edge is fringed? It seems to me, both are but I’m not sure. Wonderful flight shot either way. Love “half mast” eyes.
Patty, I’m pretty sure the owl feathers I’ve seen have been fringed on the trailing edge.
I thought the eyes looked like bedroom eyes. They look like mine this morning after only 3 1/2 hours of sleep…
Ok! You’re pretty darned cute and YOUR eyes are at half mast, too, but can you fly??? Never mind which edge of your arms are fringed on, if you can fly (quietly)who cares!…….
Thanks so much for including the link to the BBC piece–I don’t know which was more compelling–the beauty of the birds’ adaptation, or the utter delight on
the faces of the human participants witnessing and recording it . It is in seeing such reminders of the fact there are human beings capable of wonder and respect
for natural “genius” that permits me some hope for the future .
Well said, Kris. Very well said!
Ron —
I found this explanation on asknature.org. I’m not sure it totally explains the leading edge-vs-trailing edge aspects, but maybe it clears up some of the issue:
Owls are known as silent predators of the night, capable of flying just inches from their prey without being detected. The quietness of their flight is owed to their specialized feathers. When air rushes over an ordinary wing, it typically creates a “gushing” noise as large areas of air turbulence build up. But the owl has a few ways to alter this turbulence and reduce its noise.
First, the leading edge of the owl’s wing has feathers covered in small structures (hooks and bows) that break up the flowing air into smaller, micro-turbulences. These smaller areas of turbulence then roll along the owl’s wing toward the trailing edge, which is comprised of a flexible fringe. This fringe breaks up the air further as it flows off the trailing edge, resulting in a large reduction in aerodynamic noise. Then, any remaining noise that would be detectable by the owl’s prey is absorbed by velvety down feathers on the owl’s wings and legs. These soft feathers absorb high frequency sounds that most prey, as well as humans, are sensitive to.
All together, these features enable owls to remain undetected when they fly. However, it’s believed that the wing’s serrated leading edge is most effective at reducing noise when the wing is at a steep angle—which would happen when the owl is close to its prey and coming in for a strike.
Thanks, Jeff. That information is definitely helpful and I can see where some of the confusion comes from.
But this is one of the few sources I’ve seen that actually says the fringe is on the trailing edge. Others say it’s on the leading edge.
Perhaps not everything one finds on the internet is accurate… Ya think???
Ron, I’m not an expert on anything and don’t know about soundless flight, but based on your photo, it’s clear to me that the fringe is not on the leading edge of those feathers. I never had any idea of why owls are able to fly soundlessly. I’ve never heard a raptor’s wing sounds, either. The only birds whose flight I’ve ever heard is Doves and Quails.
Then maybe I’m not as dense as I thought I might be about this, Susan. Time will tell. Thanks for the feedback.