So, as I've said before, I'm a big bird fan. I'm a big bird fan primarily because these creatures so beautifully display God's handiwork. It's hard for me to see a bird and not think, "Wow! What a marvelous Designer you have!!" Consider with me, just for a moment, the amazing ... feather.
Part of the definition of all birds is that they have feathers. Now, feathers vary, of course, but they have a variety of features in common, too. Feathers provide protection, insulation, and flight capability. feathers are very important and quite unique to birds.
Feathers are structured with a central shaft and vanes radiating from that shaft. These vanes have their own central shafts called barbs with barbules sticking out of the barbs. Barbules are interlocked with a hooking mechanism (barbicels) that links barbule to barbule like Velcro, making a semi-solid but very flexible and very light surface on the feather. When birds preen themselves, one of their primary aims is to pull apart damaged barbules so they can relink.
Feathers are not random on a bird. They are in rows and columns, linear tracts called pterylae. (If you've ever looked at a plucked chicken, you can see the rows and columns of bumps where the feathers used to be.) That, you see, is a product of random chance, mindless design. Right?
There are several types of feathers. The largest are the flight feathers, called remiges. These are broken down further into primary and secondary remiges, where the primaries are on the outer part of the wing and the secondary on the inner part. Together these form large surfaces for flight. Tail feathers are called retrices. These, too, are typically large, providing stabilizer and control surfaces. Smaller feathers called coverts border the edges of the remiges and retrices to provide streamlining of the wing and tail surfaces along with some insulation. Other feathers provide insulation and waterproofing as well as varied specialized purposes.
The central shaft of the feather is hollow, making it very light. In fact, we have that term, don't we? "Light as a feather." Because feathers are, indeed, very light. And, yet, as it turns out, feathers on a bird typically weight more than the skeletal structure of the bird. Birds, you see, are designed to be fairly strong, but very light. (Oh, there's that "design" word. Hard to avoid.) That central shaft is round and hollow close in to the bird's body, but as it gets farther from the hard mount on the skin, it changes shape. The outside remains round, but the inside takes on a more rectangular shape. You see, a rectangular shape inside a round shape gives incredible strength and enables the flight feather shafts to transmit the lift and drag forces required for flight.
Feathers are shaped in a particular way. Flight feathers have precisely the same shape as your modern aircraft, without, of course, all the metal. The central shaft provides the structure, and the vanes which are shorter on the leading edge than the trailing edge give the surface. Shaped in an arc, these surfaces are designed to provide a solid surface in one direction and an aerodynamic surface in the opposite ... you know ... like you'd want it to be.
I could go on and on. This simple creature, a bird, only starts as a feathered creature. There are so many other features to birds. And don't get me started on individual birds and their characteristics. No, this was just a touch on a single component common to all birds, their feathers. The whole thing screams design, begs for intelligence, demands a Creator. They call it "irreducible complexity", and just the feather of a bird has it. In all sorts of very real ways, the heavens declare the glory of God, including the birds that fly through them. Anything else takes more faith than I have to believe.