The preserve is just behind Walmart and beside the Rona in town, which you see on your right as you enter Uxbrifge on Highway 47. When you go behind the Walmart, you'll see a little parking lot and a map of the trails. For the buntings, they're all over the trails in the preserve. Just listen for them, as they like to sit in the open at the tops of the pine trees and sing.
Mark