This is a Savannah Sparrow. One of the best ways to separate Savannah from Vesper is the back pattern; Vesper has uniform gray brown streaking extending to the nape and crown. Savannah has “braces”, pale whitish feathers in the central back that form something of a “V”; not always easy to see, but visible in your photos. Also, on the wing coverts, there is virtually no pale edging to the median or greater coverts, as per Savannah. Vesper would show white edges there. Note the eye is tiny and beady, a Savannah character. Vesper has a larger eye, and appears quite “bug-eyed”, with a thin white eyering. As for the white in the edge of the tail, Savannah has a white outer web to the outer retrice, shown in your photo.