In my night-hike tool kit, I carry two short pieces of rope: one is smooth with a well-defined edge, while the other is frayed with a tattered edge. I use them to demonstrate the stealth acoustics of owl wings.
Photo courtesy of: Lilian Holt
I begin by asking the hikers a question: When I swing each of these ropes in a circle, which one do you think will make the most noise?
After making a few loops in the air with each rope, the answer is obvious - the smooth rope makes the most noise. This leads to my second question: why do you think that is?
The explanation has to do with air turbulance. According  to Dr. Justin Jaworski, “All wings, either natural or engineered, create turbulent eddies as they cut through the air. When these eddies hit the trailing edge of the wing, they are amplified and scattered as sound.” The smooth rope creates a trailing wake of turbulence as the rope “cuts” through the air. In contrast, the rope with the frayed edge is silent, because the small trailing eddies of turbulence tend to cancel each other out.
Understanding the how leads to the third question - why do owls need silent wings? To be a successful hunter, an owl must be able to silently sneak up on an unsuspecting mouse or rabbit. Their wings and feathers are designed to help them do just that.
Owl wings and feathers have three design attributes that help reduce noise. Dr. Jaworski describes these features as "a comb of stiff feathers along the leading edge of the wing; a flexible fringe a the trailing edge of the wing; and a soft, downy material distributed on the top of the wing." Click here  to take a closer look.
The comb of stiff feathers at the leading edge of the wing and the trailing edge fringe break up the larger turbulence into smaller micro-turbulences. The fuzzy, downy material on the top of the wings may also reduce the noise level.
All this stealth technology leaves me wondering about other objects that fly through the air at this time of year. Could Santa’s sleigh have stealth acoustic design features? After all, his reindeer are furry and have fuzzy tails. And their prancing hoofs just might break up the trailing turbulence.
Something to consider, right? After all, we don’t want to wake those children nestled all snug in their beds, now do we.
Upcoming Outdoor Events:
Trail Maintenance Schedule. Come join our volunteers as they help maintain our trails. Contact Steve at email@example.com  for time and place.
Wednesday mornings, December 4, 11, & 18.
Saturday mornings, December 7 & 21.
2014 PlaceritaCanyon Wild Flower Calendar. Looking for a unique and local gift? For $10, the Docents and Volunteers at PlaceritaCanyonNatureCenter are offering a calendar filled with original photos of local wild flowers. Best of all, your purchase will help support the fine work of the PlaceritaCanyonNatureCenter. They are available at the Placerita Canyon Nature Center Gift Shop.
New trail maps available. If you’d like to explore a bit on your own, the City of Santa Clarita has a website with trail maps  of our local open spaces.
There’s also a new website for bicycle riders .
Ask Dr. Norm : Do you have questions about the flora, fauna, animals, rocks, etc. in our Santa Clarita Valley? Here’s a place for you to ask your questions. Dr. Norman Herr, Ph.D., is a professor of science and computer education at CaliforniaStateUniversity, Northridge.
Tell Us About Your Hike : Here’s a new website where you can post pictures, provide feedback and make suggestions about the City of Santa Clarita’s trails and open spaces.
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