Noticed this little female House Finch on the feeder today. It appears that she is partially blind. House Finches are prone to an eye disease called "Mycoplasmal Conjunctivitis", which causes ulcerations and crusting of the eyes. Although the eyes are what one notices, it's primarily a respiratory disease, also found in chickens and turkeys.
For now, this little gal is able to fly, although not very gracefully, from trees to feeder. And although she occasionally misses the opening in the feeder, she usually feeds very easily. However, the disease will likely kill her, or make her easy prey. Interestingly, there have been no other House Finches at my feeders for almost 2 weeks now. She is the only one.
Interesting tidbit I learned when reading up on House Finches:
House Finches feed their nestlings exclusively plant foods, a fairly rare occurrence in the bird world. Many birds that are vegetarians as adults still find animal foods to keep their fast-growing young supplied with protein.
More information on Mycoplasmal Conjunctivitis can be found here: