About the Cable Natural History Museum:
For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI, at 13470 County Highway M. The current exhibit, “Deer Camp: A Natural and Cultural History of White-tailed Deer,” opened in May 2013 and will remain open until April 2014.
The noiseless glide of soft, gray wings caught my eye. Then, stillness. No matter how hard I squinted, I couldn’t resolve the dark shape into a branch and the owl I knew had just landed there. Fading light under gray skies, combined with the owl’s pattern of light and dark bars on its chest, created perfect camouflage.
Nevertheless, I felt grateful to catch even a glimpse of such a graceful nocturnal creature. On a sunnier day, it might stay hidden against a shady tree trunk until dark, avoiding detection by its nemeses – crows or great horned owls. The gray afternoon and impending breeding season must have lured it from its usual daytime roost.
Most of my encounters with barred owls have been vocal. Their distinctive eight-note call is often phrased as "Who cooks for you? Who cooks for you-all?" and has earned them the nicknames “Eight Hooter” and “Le Chat-huant du Nord,” which is French for "The Hooting Cat of the North.” On many childhood nights, conversations between my dad and the barred owls echoed over the Iowa hills. There were also my first attempts at calling in the owls, which often got a response from the local coyote family instead.
As a Girl Scout Camp counselor, I remember a very long week in a unit of ten-year-olds when the barred owls out back decided to practice their full repertoire of calls. When the awful jumble of hoots, screeches, cackles, and yelps broke into a frenzied and raucous monkey-like squall, we ended up with a bevy of scared girls in the counselor tent—and very little sleep. I have to admit that the barred owl’s voice can still send shivers up my spine. Now, as breeding season ramps up, is a good time to listen for their haunting calls.
While their voices can be eerie, the silence of owls is even more intriguing – and lethal. Not only does silent flight enable owls to sneak up on prey, it also allows them to hear a mouse – under a foot of snow – pinpoint its location, and punch sharp talons through the icy crust with deadly accuracy. Any flight noise would obscure the soft scurries of those subnivean snacks.
One secret to silent flight is broad wings with large surface areas that reduce the need to flap. Owls just seem to float through the air. In addition, anyone looking at an owl wing can see a comb of stiff feathers along the leading edge, and a flexible fringe on the trailing edge of the wing. Those fringes break down air turbulence into smaller currents called micro-turbulences, which generate less sound. (If you’ve never studied an owl wing, then check our summer program calendar for owl prowls and raptor programs at the Museum!)
Looking closely, you may also notice a soft, downy covering on the top of the wing. A photographic study of owl feathers revealed a surprising 'forest-like' geometry of the down material, and scientists at Lehigh University's Department of Mechanical Engineering and Mechanics think that this may be another key to eliminating sound.
Dr Justin Jaworski, a scientist on the project, predicts that “If the noise-reduction mechanism of the owl down can be established, there may be far-reaching implications to the design of novel, sound-absorbing liners, the use of flexible roughness to affect trailing-edge noise and vibrations for aircraft and wind turbines, and the mitigation of underwater noise from naval vessels.”
Just being quiet isn’t enough. Owls have especially acute hearing; due in part to their satellite dish-like facial disks that funnel sound, and to a right ear that is higher on their head than the left ear. The sounds of a scampering mouse—like the ones who have left numerous hopping tracks quilted into the snow near my skis—will reach one ear more quickly than the other ear. By using this triangulation, owls can pinpoint the location of their prey—even below snow—even in complete darkness.
Once prey is located, owls’ other weapons kick in. Their sharp talons and hooked beaks are equally strong, unlike other raptors who have stronger feet and weaker beaks. Owls use both to grab, kill, and eat their prey.
The owl was still nearby, I knew, since I hadn’t seen it leave the branch. Although I couldn’t see it in the fading light, I knew its huge eyes could be watching me. Owls have excellent binocular vision, which allows them to judge distance and depth. Owl eyes are more than twice as large as the average size for birds of the same weight. In fact, their eyes are elongated tubes held in place—unmoving—by bony structures called sclerotic rings.
To compensate for not being able to move their eyes, owls can turn their heads up to 270 degrees (NOT 360) left or right from the forward facing position, and almost upside down. Owls’ fourteen neck vertebrae (twice as many as we humans), single pivot point within the cervical vertebrae, special muscle structures, and a special arrangement of the jugular veins all contribute to their flexibility.
Without downy feathers to insulate me, the chilly evening crept into my core. Pushing my skis forward, I tried to catch one more glimpse of the camouflaged critter. This tested the flexibility of my neck (only about 180 degrees), strained my human eyes, and made far more sound than those soft, gray wings.
Read more posts from Emily Stone.
Emily Stone is a Naturalist/Educator at the Cable Natural History Museum. Visit http://www.cablemuseum.org to learn more about exhibits and programs at the museum. For more from Emily Stone, visit her blog at http://cablemuseumnaturalconnections.blogspot.com/.