Diseased Bird: Pine Siskin with Lame Leg

I first noticed this pine siskin at my feeders on January 24, 2018. The bird has a lame left leg that juts out from its body and appears to be stiff and unflexible. The bird balances on its right leg to perch on the feeders and eat. From some angles, its tail feathers also appear to be skewed. The bird has been a regular visitor to my feeders since I noticed it.