Owl-natomy Mega Post: The Fabulous World of Feathers
Owl-natomy Mega Post: The Fabulous World of Feathers
After the last mega post, someone mentioned feathers as the next topic. I was amazed at the response the first write up got, so here we are again. Just a reminder, I'm not any kind of expert, so ask this is from a couple days of Internet research. If you feel I've posted something incorrect, let me know. Otherwise, I hope you enjoy!
If you didn't check out the other post today with the video, watch it here before or after reading this to see a visual demonstration of some of these abilities in action.
What Are Feathers
Feathers are probably the first thing we think of when we think about what makes birds unique from other animals. After all, they are the only living creatures to have them. Some dinosaurs and archosaurs also had feathers, so they’ve been around for a very long time. These protofeathers were most likely used to regulate body temperature.
Teraterpeton (approx. 230,000,000 BC) Note the proto feather fuzz along the topside.
Feathers are the result of follicles that produce keratin in specific sections of the skin. That is the same substance that also makes up the bird’s beak and claws, as well as reptile scales, mammal hair, horns, and hooves in those respective animals.
New feather growing out of keratin sheath (called a pin feather.)
Structure
Feathers are arranged in tracts, not spread evenly across the whole bird. Arrangements are different between species, and patterns are used to indicate evolutionary links between different birds.
Chart showing feather tracts and some general body parts.
There are 2 basic types of feathers, vaned feathers, and down feathers.
Vaned feathers have progressively smaller offshoots coming off the vane (called the rachis) called barbs and barbules. These structures will cross hatch and add rigidity and structure giving the bird its shape and provide strength for the pressures involved with flight. Feathers will be firm on downstrokes, but flex on upstrokes, increasing efficiency.
Simplified basic feather diagram
Eagle Owl feather magnified 150x showing barbs and barbules
Down feathers are fluffy due to lack of barbicles and a much thinner rachis. The spaces in this mesh of fluff leaves room to trap air to provide insulation to the bird.
Molting
Feathers are subject to wear and damage and are replaced in a process called molting. Birds do not lose all their feathers at once. It happens over about 3 months each year and occurs in an order that does not heavily impede the ability to fly or hunt. Some small owls will drop all tail feathers at once. New feathers start from a keratin sheath called a pin feather.
Barn owls molt wing feathers from the inside out. Other owls molt from the middle of the wing out to the tip and the body.
Color differences allow to see new/old feathers.
Functions of Feathers
Flight
Owls have proportionally larger and rounder wings than most birds. This high surface area to mass ratio makes them more buoyant, in turn requiring less flapping to fly, and extending glide time.
Thermal Insulation
Feathers insulate the bird itself by trapping air warmed by the owl’s body heat. This retained heat also is why birds sit on their eggs and chicks. It keeps eggs at proper hatching temperature, and the babies are not born with feathers, just a little temporary down that will eventually be replaced with actual feathers.
Waterproofing
Birds have a preening gland that secretes an oil the birds rub on their feathers. This coats the barbules and waterproofs the bird.
Coloration
A bird’s colors help in communication and protection. Some birds use color to attract attention. Owls most seem to use their coloring to blend into their environment. Coloring serves as camouflage to hide while sleeping and to stay hidden from prey.
Color comes from pigments (carotenoids, melanins, and porphyrins) in owls, while some other birds also have structures that refract light, causing iridescence. The browns in many owl feathers is froma combination of melanin and porphyrin pigments. Porphyrins reflect UV, so those colorations would appear more colorful to birds, as they can see light in the UV spectrum.
Barred Owl wing under UV light. This is closer to what birds would see.
Types of Feathers
Pennaceous feathers, also called contour feathers, are vaned and cover entire body. These are the longer, outermost feathers someone will likely picture when they think of a feather.
Semiplumes are a cross between down and contour feathers, filling in gaps and providing insulation.
Filoplumes are more hairlike. They are mostly found on the head, neck, and trunk. Not all birds have filoplumes. It is thought they are used like cat whiskers, aiding in pressure and vibration sensing. On owls, filoplumes are found at the base of the beak and the feet.
Bristles are tiny feathers with thick shaft. They are found at the base of beak, around the eyes, and the eyelashes. They help protect the eyes and aid the senses.
Bristles around eye and beak of a Boobook.
Down traps air to provide insulation. Owls have less down than other birds, and instead have more barbules on contour feathers closest to the skin.
Feather type examples.
Unique Owl Feathers
Some owls have ear flaps with feathers that protect the inner ear and base of the eyes. Owls have tubular eyes instead of round eyes, and many species will have eyes extending back into the ear opening.
Feathered ear flap of a Long Eared Owl. The bluish thing is the back of the eye.
Plumicorns, or ear tufts, have nothing to do with hearing as they aren’t next to the actual ears and are used for communication and camouflage.
Stiff facial disc feathers help direct sound to the ears. The feathers can be manipulated to hear better at different distances.
Barn owl facial disc and ear opening relation
Owls have unique leading edge to the wings called fimbriae, meaning fringe. This breaks up turbulence over the wing into micro turbulence, eliminating noise. The trailing edge also has a similar fringe. Down on some owls’ legs also functions to dampen sound.
Fimbriae on Barn Owl wing.
Possession of Owl Feathers
In the US, possession of any part of a bird is illegal under the Migratory Bird Treaty act and you can be fined and charged with a misdemeanor or felony depending on the species. This applies even to found feathers or ones from birds that died of natural or unnatural causes. There are some exceptions for hunting and there is a permitting process for research, education, or religious purposes, though it sounds difficult for an individual to acquire.
Sources
To Fuzz or Not to Fuzz: A Guide to Archosaur Integument
Anatomy and feather structure in a road-killed Barred Owl
Another great post!!
Thank you for enjoying it!
My favorite part was learning birds are living blacklight posters flying through the sky.
That and the molting process details about the shed patterns.
I want to learn more about preening, but I'm not sure everyone's feelings about bodily secretions lol. Maybe pellets and digestion. I learned owls don't have a crop like other birds, so I know that's at least one difference.
I'm fascinated by everything, so I'm good with any topic. Again, thanks for everything you do!
Owls really are all eyes, ears and fluff.
Don't forget feet!
I'm especially fascinated by the colors under UV light.
Me too! There seems to be much speculation as to what advantages seeing UV offers, and while owls lack the UV detecting cone structures in their eyes, other studies have shown the owls' rod eye structures still look to be able to detect variances in UV light levels. Some think they use this for navigation purposes, others guess detecting rodent urine trails, but I couldn't find anything conclusive.
This short article talks about how UV light can be used to determine an owl's age and inspecting molting patterns. It's a good supplement to the things in the post.
A note on waterproofing, I've heard that barn owls (and maybe some others) are not waterproof, and that's one reason they struggle sometimes. If it's constantly raining they can't really hunt.
Poor little soggy owls.
Holy heck, if you want to read conflicting information, Google "owl preening waterproof"!
I think this is one of those complex answers with a lot of fine detail. I know even the fish owls try to not get too wet. I'm sure every bird's preening oil is a bit different. I can't even find a straight answer if keratin itself is waterproof.
I did find a few ideas:
Rainy weather is very risky for owls for a few reasons:
Their feathers become waterlogged making flying difficult and therefore hunting is impossible and owls may starve.
I'm thinking the physical feather may be waterproof, but those barbicles are so close together, I'm sure water will hook onto those gaps from surface tension. With that, and owls bring up to 70% feathers by volume, you end up with a heavy bird even if the water doesn't actually soak in. Either way, weight not conducive to flight. Even if they can fly, it's going to use way more energy.
Waterlogged feathers lead to body heat loss. This can lead to hypothermia death in owls, likewise these waterlogged owls may return to their nest and then sit on their owlets or eggs. This can lead to their owlets or eggs catching a chill or worse freezing to death.
Living indoors, I overlook exposure as a source of danger, but this makes a lot of sense.
Much of owls main prey will seek shelter in wet weather meaning the owls are less likely to find prey even if flying is possible.
Chicks that fall from nests can often manage to climb back up using their talons, wings and beaks but when they are soaked through in heavy rainfall this makes it almost impossible.
I'll have to do some more reading on this to find out more.
Where sound goes to die.
Along with a bunch of tasty critters!
This is super interesting, just like the feet! I had no idea that feathers served so many different functions. Thank you for this post and also for curating the links. That takes a lot of time!
Glad you enjoyed it! Did you watch the video too?
I hope the likes jump up over the rest of the weekend! So far I could have posted a random pic and got as many! 😅
I'm starting to recognize some of you guys' user names, so at least there's a solid handful of fellow bird nerds coming here.
I like learning the little things I would never come across just finding pics though, like the ear flaps on some of the owls and how barn owls molt differently that the other owls. Just stuff I'd never think to look up in the first place.
I see lots of italicized text. Are they supposed to be links to pictures?
I just used that for the picture captions, no links. You should see the italicized text right after the pic. I embedded all the pics so you wouldn't need to navigate away and lose your spot.
It's also italics on the sub headings for the purposes of feathers section.
I like the SEM images
World famous Doctor Chopper would of course be interested in the anatomical structures! 😄
Here are some more for you then. It's impressive how much branching there actually is. These micro structures are able to accomplish so much. Insulating, waterproofing, stiffening, all from simple little strands.
Great Horned Owl
Tawny Owl
Long Eared Owl
Barn Owl compared with PigeonThis one goes very well with the video.
Details of a feather. (A-E) Details of the barn owl's feather p10. (A) Serrations at the outer vane's leading edge. (B) Fringes at the inner vane's trailing edge. (C) Velvet-like dorsal surface of the inner vane. (F-J) Details of the pigeon's feather p10. (F) Leading edge of the outer vane. (G) Trailing edge of the inner vane. (H) Dorsal surface of the inner vane; scale bar: 1 mm. (D, I) Qualitative illustration of the porosity (translucency) of black dyed inner vanes of feather gsc5 of the barn owl (D) and the pigeon (I). (E, J) Plumulaceous barbs of feather gsc5 of the barn owl (E) and the pigeon (J); scale bar: A-D and F-I: 1 mm, E and J: 5 mm.
Full research paper here for that photo: Morphometric characterisation of wing feathers of the barn owl Tyto alba pratincola and the pigeon Columba livia
I see lots of italicized text. Are they supposed to be links to pictures?