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The silence of the owls describes an interesting new look at owl flight, and a recent attempt to figure out why they are so much quieter than other birds, and quieter than just about any other flying thing. Based on this paper, https://www.annualreviews.org/doi/10.1146/annurev-fluid-010518-040436
Laboratory measurements have shown that the slight swoosh made by a barn owl is below the threshold of human hearing until the owl is about three feet away — a feat of stealth that biologists and engineers are far from completely understanding. But researchers from both disciplines are working to solve the riddle of silent flight — some with the aim of designing quieter fans, turbine blades and airplane wings.
Such owl-inspired innovations can reduce noise by as much as 10 decibels, similar to the difference in noise between a passing truck and a passing car...
...
First, Graham [1934] pointed out an unusual structure called the "comb," which literally looks like a comb projecting forward from the wing's leading edge. Second, he noted that most of the owl wing is covered with a soft layer of velvety feathers. Finally, he observed that the feathers on the trailing edge of the wing form a ragged fringe.Most researchers still agree that the comb, the velvet and the fringe combine in some way to reduce noise, but the owl may have more tricks up its sleeve. "When all is said and done, I think we'll have a number of mechanisms, including Graham's," says Clark.
The article goes on to quantify the sound of an owl relative to human hearing. Also shows some CFD that purports to show tiny vortices shed off an owl wing, these rotate both ways and there is the possibility of destructive interference.
Journal Reference:
Justin W. Jaworski and N. Peake. Aeroacoustics of Silent Owl Flight, Annual Review of Fluid Mechanics Vol. 52:395-420 (DOI: 10.1146/annurev-fluid-010518-040436)
Once, sitting around a dying campfire in the north woods with a few friends, we all noticed a presence overhead, the barest of swishes, could have only been an owl. It was a pitch black night, we never saw a thing.
(Score: 2) by Runaway1956 on Sunday April 26 2020, @05:30AM (5 children)
When we moved into this plant, it had been vacant for years a few years. Went out to an outbuilding, that had been used to clean things on one side, and to transfer heavy items with a crane on the other side. There were no doors on the building, it's just open on both ends. Shining a little flashlight, I found the breaker box, and flipped breakers to turn the lights on. 5 ghostly white things just fell out of the overhead structure, and floated away. Not-quite-silent, but very very close to silent. Yes, it scared the bejeezus out of me, but I did have time to get a pretty good look at them.
I've never positively identified them. Barn owl is close, but these guys seemed large for barn owls. And, they were almost all white. Look at pics of barn owls, and there's a lot of brown markings all over, only the face is white. I suppose there is variance among barn owls, but I've not found photos of barn owls with so much white as these guys had.
The owls had returned the next night, and I got another good look at them. I got to see them a few times over the next month or so, but eventually, they just stopped coming back. Too much noise, and they didn't like the lights. I really should have got some pictures and posted them online to get positive identification. I want to call them snowy owls, but Arkansas isn't in the arctic. Guess I'll never know for sure what kind of owls this family is. The largest of them probably had a 4 foot wing span, the smallest was right around 3 feet.
Having the owls around was kinda cool, but I guess they thought we were horrible neighbors, with all the noise and fuss, and bright lights all night long.
(Score: 1, Informative) by Anonymous Coward on Sunday April 26 2020, @07:35AM
When I went to a lecture on ornithology, I remember them telling us that Owl coloration depends on the variety, habitat, and time of year. As an example, look at the different coloration and combinations you can see here: https://www.allaboutbirds.org/guide/Barn_Owl/media-browser-overview/ [allaboutbirds.org]
(Score: 0) by Anonymous Coward on Sunday April 26 2020, @09:04AM (2 children)
Ghosts, Runaway1956, ghosts of Union organizers past. You should have paid them heed.
(Score: 2) by Bot on Sunday April 26 2020, @11:22AM
Union organizers go to hell so quickly, you're unlikely to find them above ground in ghost form.
JK some union organizers were heroes. The net effect of the movement and its ties with the system, though, are highly debatable topic...
Account abandoned.
(Score: 0) by Anonymous Coward on Sunday April 26 2020, @11:42AM
We paid them, in lead, one ounce at a time.
(Score: 2) by Bot on Sunday April 26 2020, @11:19AM
>Yes, it scared the bejeezus out of me
I guess they went O RLY? too.
Account abandoned.