Halloween Mask? Sick?

Nope. This is a molting juvenile Cardinal getting his adult plumage in. Perhaps born early summer. I have been watching him get his adult feathers in and I think it is safe to say he is going to be a boy. You can see his dark black mask emerging. You can also see the juvenile black beak turning orange as he builds more and more carotene from seeds. He is eating sunflower seeds here. 

Our adult cardinals are getting a new set of feathers as well. They are very quiet, no singing, in hiding as it takes a great deal of energy to get new feathers in which they do once a year. It is an important time to keep the feeders going as they have very little energy to hunt during this time. It generally means they are done with mating season but some cardinals likely have one more brood which will fledge by mid October. Not all on the same schedule.