White Wagtail, "Nope, wasn't me....."
During summer many people see what appear to be bald cardinals visiting your yard or feeders. Dont be alarmed. This is a relatively common phenomenon in Cardinals, as well as other species, particularly Blue Jays. The birds normally are not sick, and the feathers will soon grow back.
There are several explanations for this loss of feathers. First, this total feather loss may be a normal occurrence for individual birds during their post-breeding molt. The loss may also be caused by mites - in this case skin mites. The mites are perfectly natural (and not caused by diet) and relatively harmless, unless the bird is in an otherwise-weakened state. The mites exist on the birds in the only place the birds cannot preen themselves-on the head. They should have a new set of head feathers in a month or so.