This has been a good winter for Pine Siskins at the feeders. Unfortunately, when you have large flocks of siskins, it is not uncommon to find sick individuals. These birds are susceptible to both respiratory and eye diseases, both of which can be transmitted to other birds through close contact. It is important to keep your feeders clean and remove debris from underneath on a regular basis. If you see more than a few sick birds, take the feeders down for a couple of weeks so the birds will disperse.
In this photo, the sick individual stands out by being much more “fluffy” than the other birds. Sick birds will also be lethargic, sometimes going to sleep at the feeder.