With your wing shape post what shape would flightless birds have? (Chickens, ostriches, kiwis, etc) Or do they all have different types?
Chickens aren’t fully flightless but they are so very bad at it, bless their hearts. They have an elliptical wing, the problem is that it’s too small relative to their body, and the corresponding flight muscles are underdeveloped.
To be clear, flightless birds aren’t flightless strictly because of their wings. Most have lost their keel—it’s a little bone growth on the front of the sternum (breastbone) where flight muscles attach. No muscles, no power, especially when the body mass is high as with many flightless birds. So, even if you were to stick proper wings on these guys, they’re not going to be taking off.
With that in mind, no, many flightless birds don’t have a wing shape comparable to flighted birds. Their wings are no longer under selective pressure to be functional for flight and were therefore able to undergo a lot of changes that flighted birds wouldn’t tolerate. Feathers need to be stiff and grow in a certain aerodynamic pattern, but flightless birds have lost or dramatically rearranged feathers, and their feathers are often soft and oddly shaped…and the sum of these effects makes the overall wing shapes weird.
Ostriches, for example, resemble…nothing. Like, look at that. That’s a craft project. They now use their wings for mating rituals and other displays, as well as some general braking/turning assistance while running. (That assistance basically amounts to “fancy rudder” though, and isn’t a particular special shape from what I was able to find.)
(Image source and also a cool article on possible similar wings in dinos)
Their overwing feathers are fairly uniform and soft, the underwing is totally unfeathered, and they’ve gained long feathers on both the leading and trailing edge of the wing, none of which would be allowed to happen in a flighted bird because it’s an aerodynamic disaster. Rheas are like this too. Here is a very viscerally unpleasant picture from the underwing of an ostrich…
Here is all the grandeur of an emu wing.
(Image source) (Thanks @reggiemess and anon for the pic/correction!)
But there are a few cases of recognizable wing shapes. These are all shapes that came from the flighted ancestor; they weren’t developed anew during flightlessness. The species just hasn’t messed too much with the wing pattern, whether that’s due to a recent loss of flight or a neutral/positive selection towards the old feathers.
Kakapos fall into this situation. Kakapos have the chicken problem. That’s a fairly standard wing, but too short for its body mass and with no flight muscles. They’re still good for balance, though.
There’s also a flightless cormorant. No, this bird isn’t sick or molting—this is what their normal feathers look like, and they’re used for swimming and diving. It’s still approximately a normal cormorant wing, they’ve just significantly reduced the feather length and coverage.
Please also have this great rhea pic I came across in the process of finding images for all of this.