Subject: Strange behavior for a cardinal

I live on a man-made lake with many birds.  The housing is relatively 
close (5-15 feet between homes).  There is a cardinal that flys between my 
house (garage window) to my neighbor's house (garage window) and "slams" 
into each like he is protecting his territory.  I wonder if he thinks he 
is fighting off his reflection?  I feed him regularly and think he will 
nest...just wondering about the rather strange behavior of "slamming" into 
windows...back-and-forth.

Re: Strange behavior for a cardinal