Back in mid-November, I noticed a dark-eyed junco with an apparent broken wing foraging under the feeders. Needless to say, this bird became a favorite as it seemingly dragged its wing and, admittedly, I looked for it daily to see if it was 'ok'. (It was able to make short but slow flights to the safety of a shrub.)
While out trying to get photo of a white-throated sparrow, the junco landed quite close to me so I snapped a few photos and studied it more closely.
I discovered the wing was not broken but was used as a 'brace' because the junco had only 1 leg. It learned to balance itself with the opposite wing. Adaptation. (Maybe an avian Tiny Tim.)
It was missing from the yard for the past two weeks and I assumed it succumbed to the elements or a predator (e.g. cat). But today, it returned, in the deep snow, foraging laboriously but successfully. An amazing little bird.
(I'll post a photo on ebird today if anyone is curious about this bird.)