A co-worker is currently being plagued by a female Northern Cardinal that
sits on a window sill and incessantly pecks the glass.   It apparently gives
a steady, rhythmic tap, without fluttering.  And does so for hours.  A male
sits nearby and watches.  The curtains are closed.  

As near as I can tell, this is not a situation of the bird attacking it's
reflection, taking it for a potential rival.  I've consulted the Stokes
behavior guide, as well as the on-line BIRDS OF NORTH AMERICA, and have not
turned up an examples of similar behavior.

Anybody have a clue?  I'd rather not clog up the listserve, so please reply
off-line, unless you think your solution to this puzzle would be of general
interest.

Kurt Schwarz
HowCo
goawaybird at comcast dot net