The prothonotary warbler is unlike any other eastern U.S. wood-warbler species, as it prefers to build its nest in tight cavities (4) (6). This species is highly opportunistic and will nest in many types of small, sheltered, and cramped spaces in wet forests and swampy areas. The nest may be built in natural cavities, such as holes in trees, or in man-made cavities including next boxes and discarded refuse, such as milk cartons, cans and jars (5) (6). The prothonotary warbler may also use holes excavated by the downy woodpecker (Picoides pubescens) (4).
The diet of the prothonotary warbler consists primarily of insects, such as beetles, moths, butterflies, spiders, caterpillars, and insect larvae, which are collected from tree trunks, fallen trees and leaf litter on the forest floor. It will also feed on snails and isopods, and will supplement its diet with fruits, seeds and nectar (3) (4) (5).
The male selects and prepares a nesting spot before attracting a mate, and lines the nest cavity with moss (3) (4). The male may build “dummy”, non-use, or “trick” nests to expand its territory and to provide optional nesting sites (2). The male may stay overnight in one of the trick nests to give the impression of occupancy (2).
The female prothonotary warbler takes over nest building once a pair has formed, adding nesting materials such as rootlets, plant down, grape plants, cypress bark, sedges, tendrils, leaves, stems and leaf stalks, poison ivy, and even fishing line to the nest cup (3).
Three to seven creamy-white eggs with purplish spots are laid by the female prothonotary warbler in late May to mid-June (3) (6) (7), and the female incubates the eggs for around 12 to 14 days (3). The eggs usually hatch within 12 hours of each other, and the newborn nestlings remain in the nest for the next 10 to 11 days, until the adults coerce the young to leave the nest cavity (3). Both of the adult prothonotary warbler’s share parental responsibilities, such as bringing food to the young and protecting them against intruders. The adults continue to supervise the fledglings for around 35 days after they have left the nest (3) (4).
The prothonotary warbler is extremely territorial during the breeding season. The male defends the territory by chasing away intruders or snapping its bill, while the female commonly enters into bill-snapping disputes with other females. The prothonotary warbler is generally social during the rest of the year (3).