According to the Audubon guide, males arrive on nesting grounds about a week before females and establish territories by singing and vigorous displays. They place small amounts of moss into the nest cavity, building dummy nests, but only the female builds the real nest, filling the cavity nearly to the entrance hole with moss, dry leaves, twigs and bark.
Breeding as far north as in Wisconsin is uncommon. Ever since Bill Barker and Mark Trewartha installed tiny birdhouses for Prothonotary Warblers in various places of the Picnic Point marsh to provide nesting opportunities for them, bird enthusiasts have flocked to this place. The name "Prothonotary" originally referred to a group of official scribes in the Catholic Church who wore bright yellow hoods, as this bird appears to do. (see