I am just learning about birds since I am very near a bald eagle nest on the CT 
River.  I have seen a medium size bird with a robin type beak that it all black 
except for a very clearly delineated white rectangle on its throat.  I have seen it 
very clearly twice as it flew over my kayak  on two occasions this summer.  Its 
call is a sort of repetitive non musical sound that repeats about twelve times and 
then stops then starts again.

I have looked in many books and ipad aps.  What is it?