Owls - Come on and Shake Your Tail Feathers!
Part III of a Series
A Group of Owls is Called a Parliament
Contour Feathers - cover the body, wing (remiges) and tail (rectrices)
Feathers! Oh those lovely feathers! How many feathers can a bird possibly have? Reportedly, the low count, contour feathers only, would be on a hummingbird which is 940. The highest count would be on a Tundra Swan, counted very patiently at 25,216, contour feathers only. Of these, 80% were on the head and neck. Hopefully there aren't any birds sitting around counting the number of hairs we have on our heads. (Note: Contour feathers are what you see when you look at a bird - the "outer shell" of the bird's feather coat.)
Did you know there are feather muscles? These specialized muscles are located beneath the surface of the skin around the follicle and helps to position the feather. There are also muscle sheets beneath the skin that act with the individual feather muscles to coordinate movement of the feathers within a tract.
The large flight feathers on the wings are called remiges, and the tail feathers are called rectrices. Remiges provide lift and propulsion and are attached firmly to the bones of the wing, either directly or indirectly via ligaments. The rectrices are connected to one another by ligaments, with only the innermost attaching directly to the tail bone via ligaments.
The outermost remiges are called the primaries. The primaries are attached to the skeleton of the "hand." Birds commonly have between 9 and 12 well developed primaries, which are strong and flexible.
Projecting rearward from the forearm of the bird wing is another row of remiges that are called the secondaries. Flapping and soaring flight are achieved by the secondaries which provide lift and function like the fixed wing of an airplane. Secondaries can range from 8 to 32 in number, depending on the bird.
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Ah, the tail feathers. There's a whole lot of shakin' goin' on there, isn't there? That's because the tail feathers are one of the major flight feathers in most birds and they are called the rectrices. Just like when you are out on the dance floor shakin' your tail feathers, they are needed for stability and control. Maybe you don't use them in flight like birds do, but they are important none the less. You can't be all unstable and out of control out on the dance floor, and birds can't be all unstable and out of control in the air.
Covert operations: no, don't start getting all political on me here. I'm talking coverts, which are the rows of feathers bordering and overlying the remiges and rectrices on both the upper and lower sides. These are the feathers that provide insulation, color, and pattern on the wing surface and contribute to the streamlined shape of the wing and tail. Streamlining greatly reduces the energy needed to fly, just like on aircraft.
Bristles - are small feathers with a stiff shaft and barbs only on the base, or often not at all. Bristles occur most commonly around the base of the bill, around the eyes, and as eyelashes.
Semiplumes - function to fill in between contour and down feathers.
Filoplumes - are hairlike feathers that consist of a very fine shaft with a few short barbs at the end. They are typically covered by other feathers, and may function as pressure and vibration receptors - they sense the location of other feathers so they can be adjusted properly.
Down Feathers - these soft and fluffy feathers trap air and create a layer of insulation next to the bird's body.
Ok, here is something you might really be interested in. Did you know that now only can birds shake their tail feathers, but they really, really know how to GET DOWN? I mean they really get down! And they not only get down but they get BODY DOWN! Oh! My! But they don't get down the way you all get down. They grow it.
Down feathers, those marvelous insulators, include body downs and natal downs. Body downs are the downs of adult birds and are most common in water birds. You've seen a mess of crazy ducks having a grand time in water you wouldn't dream of swimming in because it's so cold, haven't you? Ducks aren't dumb, they wouldn't go with without an insulated wet suit on. The reason their legs and webbed feet don't get cold will be in another post, that's pretty cool, too!
Natal downs are only around the time of hatching and are prominent on newly hatched chickens and ducklings, giving them their soft, fluffy look. Not all birds have natal down. In fact, "naked as a jay bird" is quite correct. Blue Jays, and most passerines (song birds), don't have natal downs. The less natal down a baby bird has, the more easily and quickly it can be warmed by it's parent. Chicks that leave their nests quickly (chickens, ducks), or remain in the nest for weeks at a time (hawks, owls) usually have a covering of down.
Powder downs are another form of down but it is not entirely understood. Imagine that? Our scientists haven't figured everything out yet! Powder downs are never molted. The grow continually and disintegrate at their tips to produce a fine powder, similar to talcum powder. It's thought that powder downs help with waterproofing and prevent staining of the feathers and are only found in certain taxonomic groups like herons and pigeons. And they can be clustered in groups on the body, or spread out among the body downs.
What the hell, Cathi? What's all this have to do with owls? We know owls have feathers!
Yeah, yeah, y'all know everything, I see. Well then, I'm sure you know that owls have silent flight. They are the B-2 Stealth Bombers of the animal world. Ok, smarties, if you know that, then can you tell me why? Can you tell me anything about the pile on the dorsal surfaces of inner vanes? Ha! Didn't think so!
The most unique adaptation of owl feathers is the comb-like or fimbriate (fringe-like) leading edge of the primary wing feathers referred to as "flutings" or "fimbriae". With a normal bird in flight, air rushes over the surface of the wing, creating turbulence, which makes a gushing noise. With an owl's wing, the comb-like feather edge breaks down the turbulence into little groups called micro-turbulences. This effectively muffles the sound of the air rushing over the wing surface and allows the owl to fly silently. There is also an alternate theory that the flutings actually shift the sound energy created by the wingbeats to a higher frequency spectrum, where most creatures (including prey and humans) cannot hear.
Most owls have relatively large, rounded wings. The wings are broad, with a large surface area relative to the weight of the bird i.e. a low wing loading. This allows them to fly buoyantly and effortlessly, without too much flapping and loss of energy. They can glide easily and fly slowly for long periods of time. Many species use this slow flight to hunt ground-dwelling prey from the air.
Other areas on the owls' wings and legs are covered with velvety down feathers that also absorb sound frequencies above 2,000 hertz. All of this makes owls completely silent to their prey.
Below is a picture of a Barred Owl feather on the left and a Mourning Dove on the right. Do you see the comb-like or fimbriate (fringe-like) leading edge of the primary wing feathers referred to as "flutings" or "fimbriae"? This is what NASA researchers have been looking at to incorporate owl-feather-inspired technology to dampen sound in aircraft. Engineers are trying to come up with a design that does not create extra drag when aircraft have reached cruising speeds and altitude. Major airports like O'Hare and Heathrow have requirements on the amount of noise per day an air carrier can generate. If they can reduce the noise, there can be more flights coming in per day. It is hoped that these ideas will get an airplane quiet within 20 years and even more quiet within 20-50 years.
|Otus brucei||Pallid Scops-Owl|
|Otus scops||Common Scops-Owl|
|Bubo bubo||Eurasian Eagle-Owl|
|Strix aluco||Tawny Owl|
|Athene noctua||Little Owl|
|Athene brama||Spotted Owlet|
|Asio flammeus||Short-eared Owl|
|Small squat owl, grey (gray) brown above with white spots, pale below with dark barring. Facial disk bordered with white and with white “eyebrows”. Yellow eyes.|
|19-21cm/7 1/2"-8 1/4", 110-120g/3.88 oz - 4.23 oz.|
|S Asia from Iran across the Indian sub-continent (except Sri Lanka) to Vietnam.|
|Open or semi-open country including semi-deserts, cultivated areas and mangroves.|
|Mainly invertebrates, also rodents and small birds and lizards.|
|November -April depending on region. Nests in cavities in trees, walls, buildings etc. 2-3 eggs, incubated for 28-33 days. Young fledge at about 32 days and remain with parents for a further 3 weeks.|
|Plaintive double whistle, “plew plew”.|
|Not globally threatened and tolerates human activity. dramatically in recent years.|
|Despite being locally very common and often living close to human habitation, relatively little is known about this owl.|
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