Prothonotary Warblers breed in flooded bottomland forests, wooded swamps, and forests near lakes and streams. They tend to avoid forest patches smaller than about 250 acres or forest borders less than 100 feet wide. During migration they stop in coastal areas, marshes, citrus groves, and scrub to refuel. During the winter, they are most common in mangrove swamps, but they also use tropical dry forest and wooded areas near streams.Back to top
Prothonotary Warblers eat spiders, butterflies, moths, beetles, flies, caterpillars, mayflies, midges, grasshoppers, ants, and leafhoppers. They also eat snails and mollusks. During the nonbreeding season they eat fruit and seeds in addition to insects. Back to top
The Prothonotary Warbler places its nest in holes created by woodpeckers and chickadees, in natural holes in standing dead trees, and in nest boxes. The male selects several nesting sites throughout his territory, but the female ultimately selects which one to use. Nests are often near or over standing water in bald cypress, willows, cypress knees, and sweetgum trees. Nest height ranges from about 2–33 feet above the ground, depending on availability of nesting holes.
The male places moss inside the hole prior to attracting a mate, but the female builds the remainder of the nest with rootlets, plant down, grape plants, or cypress bark. She lines the cup-shaped nest with grasses, sedges, rootlets, old leaves, and poison ivy tendrils. It takes the female 3–8 days to build a nest. The entrance hole to the nest cavity is around 2 inches across. The nest cup is about 2 inches wide.
|Clutch Size:||3-7 eggs|
|Number of Broods:||1-3 broods|
|Egg Length:||0.7-0.8 in (1.8-1.9 cm)|
|Egg Width:||0.6-0.6 in (1.4-1.5 cm)|
|Incubation Period:||12-14 days|
|Nestling Period:||9-10 days|
|Egg Description:||White spotted with rust-brown to lavender.|
|Condition at Hatching:||Helpless, eyes closed, with minimal down.|
Prothonotary Warblers forage in the understory, slowly hopping along branches, twigs, and on the ground in search of food. Sometimes they climb up tree trunks and pick insects off the bark similar to the way a Black-and-White Warbler forages. When the male establishes his territory he searches for potential nesting sites in standing dead trees and places a layer of moss in each hole. He selects a few good spots and displays in front of each site for the female. He flies slowly up above the tree canopy with tail spread and slowly flutters back down. To entice the female to check out potential nesting sites, he enters and exits the hole several times. As soon as the female selects a site, she starts building a nest. On the breeding grounds males and females aggressively defend their territories, chasing away intruders with snaps of their bills and sometimes with physical attacks. They are monogamous and maintain their bonds during the breeding season. Occasionally they stay with the same mate the following season. They also tend to return to the same breeding site in subsequent years, especially if they successfully raised offspring at that site. Raccoons and snakes are frequent nest predators. Brown-headed Cowbirds also affect nest success. Cowbirds lay their eggs in the nests of Prothonotary Warblers, forcing the warblers to raise cowbird young at the expense of their own. They are not territorial on the wintering grounds and in some locations they make short-distance movements to take advantage of seasonal resources. Groups of Prothonotary Warblers forage together on the wintering grounds and they also join mixed feeding flocks. Back to top
Prothonotary Warblers populations declined approximately 0.7% per year, resulting in a cumulative loss of about 31% from 1966 to 2019, according to the North American Breeding Bird Survey. Partners in Flight estimates the global breeding population at 2.1 million and rates them 14 out of 20 on the Continental Concern Score indicating a species of high conservation concern. Partners in Flight includes Prothonatary Warbler on the Yellow Watch List “D” for species with population declines that have moderate to high threats. As habitat specialists, these warblers are vulnerable to the loss and alteration of forested wetlands on their breeding grounds. Removal of standing dead trees and channeling of streams can affect availability of nest sites as well as nest success. Nests above standing water greater than 11 inches deep were less likely to be depredated by raccoons than those in shallower areas. Prothonotary Warblers are also vulnerable to the loss of mangroves on their wintering grounds along the coast of Mexico and Central and South America due to coastal development and aquaculture. Installation of nest boxes with predator guards and restoration of natural flood regimes to forested wetlands on their breeding grounds have been successful at increasing local populations.Back to top
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