Hello Tom, 

Just one pair of Bank Swallows nesting would be  unusual as it is a 
colonial species.  The situation you describes is  similar to where I have found 
nesting Northern Rough-winged  Swallows.  

Cheers, 

Rob Hilton
 
This is possible.  I didn't get a close look at the  adult, didn't have 
binoculars, and was in a hurry.  If I get the  chance will check it out.
 
Tom Beal




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