Savannah Sparrow - Passerculus sandwichensis mediogriseus - Bruant des prés
Nelson's Sparrows were singing deep from the salt marsh at Castalia on Grand Manan. Savannah Sparrows were in the slightly higher and dryer grass up to the rose bushes that line the end of the access road. For vocalization, their collection of trills and buzzes is a more complex song than the Nelson's Sparrow's effort, but it still doesn't really qualify as melodic.
This is the Passerculus sandwichensis mediogriseus form of the bird, which breeds from southeastern Canada to the northeastern United States; wintering in the southeastern US.