ID Tips: Vesper Sparrows have complete, white eye-rings, white outer tail feathers (most visible in flight) and a song somewhat like that of a Song Sparrow (listen to the following example).
Though there are exceptions, locating a Vesper Sparrow requires visiting a specialized habitat. During breeding season, Vesper Sparrows favor open grasslands with some bare ground, e.g., blueberry barrens and other sites managed by periodic burning. In southern Maine, Kennebunk Plains WMA is home to a small number of Vesper Sparrows (including the individual featured here).
MassAudubon has a map of New England and New York Vesper Sparrow occurrences along with a more in-depth discussion of their habitat preferences. And, eBird can help you locate Vesper Sparrow spots near you (click on this map, enter your zip code in the location field and/or zoom as needed).