Locality seems the best guide to identification of this shy, rare bird. I have been sure of seeing them only three times in my life. They prefer beach grass areas near the ocean and run like mice instead of flushing.
A gray Song Sparrow on an ocean beach is quite likely to prove an IPSWICH. The only note I ever heard was a single chirp. The mystery of the nesting grounds was partly cleared when they were found breeding on Sable Island off Nova Scotia.
North Atlantic coast from Nova Scotia south in Winter to Georgia.