I am sure this is the same one that earlier had just the side feathers of its head missing. It has shown normal activity.
Here is the explanation: http://www.tulsaaudubon.org/bald_cardinals.htm and http://www.hiltonpond.org/ThisWeek030701.html
A closer shot here (or hit "next"): http://www.pbase.com/m3ling/image/63833107