These warblers are small songbirds that migrate long distances in early spring to establish their nesting areas. This particular warbler foraging around the edge of some standing water, hopping along the ground searching for food and of course building materials for the nest. It flies between trees and shrubs with heavy wingbeats in an undulating patternTwo days later I believe she / he moved to another location and abandoned the site. On a second visit, I spotted the Prothonotary Warbler (Protonotaria species in nearby trees and were engaged in courtship but not coming back to the box. I suspect they had decided to build elsewhere more secure and higher up out of the prying eyes.