A prothonotary warbler admiring himself in a slough (pronounced slew)
Males select at least one cavity and place moss inside prior to attracting a mate. Females then build the remainder of the nest with a foundation of mosses or liverwort. The nest cup is made of rootlets, plant down, grape plants, or cypress bark lined with grasses, sedges, tendrils, rootlets, leaves, petioles, poison ivy, and even fishing line. The nest cup is about 2 inches wide.