The Ipswich Sparrow is a large, gray subspecies of Savannah Sparrow usually found on the coast. It breeds on Sable Island off Nova Scotia and winters south to Florida. It used to be considered a separate species.
It has been suggested that the flight call of the Ipswich Sparrow may be higher and buzzier than that of the nominate species (Flight Calls of Migratory Birds, Evans and O'Brien).
Intrigued by this, I recorded a number of Ipswich Sparrows at the New Jersey shore and compared the calls with my recordings of nominate Savannah Sparrow.
(six different birds, Jan, NJ)
Nominate Savannah Sparrow:
This Ipswich Sparrow gave some shorter, less buzzy calls, that appear more similar to nominate Savannah than the others. The bird was a little agitated, which may have affected the calls (Jan, NJ).
Flight calls of Ipswich Sparrow in these recordings are consistently more modulated towards the end and average longer (82ms vs 63ms, with some overlap, but see below), and average slightly lower in frequency. Some Ipswich Sparrow calls are similar to those of nominate Savannah Sparrow, but I have so far not recorded a nominate Savannah Sparrow giving a call like the typical modulated Ipswich Sparrow flight call.
I recently recorded a nominate Savannah Sparrow that had a longer and lower flight call.
It appears that the degree of modulation of the call is the consistent difference between the nominate and Ipswich races, at least in the northeast US.