Prothonotary warblers are stunning yellow songbirds that breed in swamps and flooded timber in the eastern United States. Their bright plumage makes them stand out against the dark water and vegetation where they build their nests. Understanding where these birds nest and their nesting requirements can help efforts to conserve this declining species.
Nesting Habitat
Prothonotary warblers are very particular when it comes to choosing nesting sites. They nest in flooded bottomland hardwood forests, wooded swamps, and slow-moving streams. The ideal nesting habitat has the following features:
- Standing or slow-moving water – Prothonotary warblers look for wetland areas with water up to 1 meter deep.
- Dead trees or snags – They nest in cavities in dead or partially dead trees (snags) that are partially submerged in water.
- Little understory vegetation – Open understories allow them to fly freely to and from nests.
- Proximity to water – Nests are almost always over or within 1-2 meters of water.
Flooded forests provide the right mix of water, dead snags for nesting, and open understory for foraging on insects. These bottomland ecosystems have declined by about 80% since European settlement, leaving prothonotary warblers without nesting sites in many areas. Preserving and restoring their nesting habitat is crucial for prothonotary warbler conservation.
Tree Species
Prothonotary warblers are not particularly picky about the tree species they nest in, as long as they are standing dead or partially dead trees in flooded areas. Their nests have been documented in:
- Cypress
- Willow
- Oak
- Ash
- Maple
- Birch
- Sycamore
- Bald cypress
- Tupelo
They readily accept nest boxes placed in flooded areas as substitute nesting sites. Ideal nest boxes mimic the cavity dimensions of natural nests in snags.
Nest Locations on Trees
Prothonotary warblers choose nesting sites from 0 to 20 meters high in trees. Most nests are found in the lower half of the tree at an average height of around 4 meters. Nests are typically built over water or very close to the water’s edge. Cavities with nests are almost always on the side of the trunk facing the water.
Nest Description
The nest itself is neat, compact cup fitted snugly inside the tree cavity. It is constructed of materials gathered from the surroundings like mosses, bark, leaves, grasses, and tree roots.
- Nest dimensions range from 6-13 cm high and 5-11 cm across.
- Nest depth ranges from 3.5-10 cm.
- The inner cup is lined with softer materials like fine grasses, moss stems, cattail down, animal hair, and cypress bark.
Females build the nest alone over the course of 3-5 days while the male perches nearby and sings. She shapes the nest to precisely fit the chosen cavity, forming a deep compact cup to cradle eggs and chicks. New nests are built each breeding season. Nests are occasionally placed on top of old nests from previous years.
Clutch Size
Once the nest is complete, the female lays a clutch of 3-6 eggs. The eggs are creamy white with brown speckles concentrated around the larger end. On average, a prothonotary warbler clutch contains 4-5 eggs. The female lays one egg per day until the clutch is complete.
Incubation
Only the female incubates the eggs. She sits tightly on the nest, leaving only briefly and infrequently to forage. Incubation lasts for 12-14 days before the eggs begin to hatch. The chicks all hatch within 24-48 hours of each other.
The male plays no role in incubating the eggs but he does bring food to the female while she incubates. His mate-feeding allows her to stay on the nest and maintain the necessary high, constant temperature and humidity levels eggs require for development.
Nestlings
Both parents feed and care for the nestlings. They bring a wide variety of insects and spiders to the demanding chicks. Nestlings fledge at 9-13 days old, a rapid rate of development compared to many songbirds. Just before fledging, nestlings cling to the cavity opening practicing wing flapping in preparation for their first flight.
Parents may continue bringing fledged young food for several days after they leave the nest. The bright yellow males take the lead caring for fledglings while females often start second broods in new nests.
Nest Failures
Many things can lead prothonotary warbler nests to fail before young fledge:
- Predators – Snakes take both eggs and nestlings. Squirrels, raccoons, and chipmunks may also raid cavities. Even turkey vultures poke their heads in to eat eggs.
- Competition – Other cavity nesters compete for the warbler’s nest holes. Bees, chickadees, nuthatches, tree swallows, and screech owls may take over cavities.
- Weather – Flooding and storms can wash away nests. Cold snaps and heat waves put nestlings at risk.
- Parasitism – Brown-headed cowbirds lay eggs in warbler nests, causing failure as cowbird chicks outcompete warbler young.
- Disturbance – Human activities like logging near nest sites may lead parents to abandon nests.
High quality habitat with plenty of nesting sites helps reduce competition and parasitism risks. Careful flood and forest management can limit weather and disturbance issues. Protecting wetland ecosystems benefits prothonotary warblers and maintains their unique nesting habitat.
Interesting Facts About Prothonotary Warbler Nests
Beyond the basics, there are some fascinating additional facts about prothonotary warbler nest sites revealed by ornithological research:
- They show high nest-site fidelity, often returning to the same cavity or tree for multiple years.
- However, only around 40% reuse exact cavities and less than 30% reuse the same tree.
- Males arrive before females in spring to establish nesting territories.
- Females heavily consider male quality when choosing a mate and nest site within his territory.
- Occasionally a female will nest in the territory of an unmated male. He helps feed her young despite no mating.
- Cavities with more vegetative cover above the opening are preferred nest sites.
- Entrance orientation does not seem to matter, with nests found facing all directions.
Detailed long-term monitoring provides much of this information about nest sites. Banding studies tracking individual prothonotary warblers are particularly helpful. Analyzing characteristics of chosen nest cavities gives clues into nest preferences.
Prothonotary Warbler Nesting Across Their Range
Prothonotary warblers breed across a wide swath of eastern North America. Is nest site selection consistent across their full range? Or do nesting behaviors differ by region?
United States
In the United States, prothonotary warblers nest from Minnesota and Iowa east to New Jersey and south to Texas and Florida. The densest populations are found along the Gulf of Mexico and southern Atlantic coasts.
Habitat use remains similar across the U.S. range – they nest in dead trees and snags over water in wooded wetlands. Natural tree cavities are preferred everywhere, but they readily use nest boxes in many areas, particularly where snags are scarce.
One interesting difference occurs in the arid southwest part of their range. In states like Arizona, New Mexico, and Texas, prothonotary warblers are sometimes found nesting along desert streams in willows and cottonwoods. This drier habitat contrasts sharply with the typical swampy forest nest sites.
Mexico and Central America
Prothonotary warblers winter in Mexico, Central America, and northwestern South America. Little detailed nesting information exists from tropical areas. But evidence suggests they nest in wet lowland tropical forests, mangroves, and wooded wetlands, mirroring habitat choices in temperate regions.
One report from Guatemala found a nest 10 meters up in a cavity in a living oak tree. epiphytes covered the tree concealing the nest hole. This highlights how abundant epiphytes likely provide alternative nesting cover in Central America where snags are scarce in the humid climate.
Caribbean
In Caribbean island habitats, prothonotary warblers display more adaptive nest site flexibility. On islands without suitable flooded forests, they utilize a wider variety of trees for nesting including mangroves, coconut palms, and beach almond trees. Nest heights range from ground level up to 9 meters high.
The availability of tree cavities and competition from other cavity nesters heavily influences nest site selection and nest height in Caribbean populations. The birds choose what’s available in each unique island habitat.
How to Provide Prothonotary Warbler Nesting Sites
Providing nest boxes and preserving/restoring flooded forest habitat are two ways to aid prothonotary warbler nesting:
Nest Boxes
Specially designed nest boxes can replace natural cavities where snags are limited. Boxes should:
- Be made of wood – PVC accumulates harmful heat
- Have a 1.5-2 inch diameter entrance hole
- Be at least 8 inches deep
- Have ventilation holes near the top
- Be installed at eye-level over water
- Have predator guards to block raccoons, snakes, etc.
- Be monitored and cleaned regularly
Ideally, groups of 5-10 boxes are installed to give the warblers options. Clumping boxes mimics their colonial, semi-social nesting habits.
Habitat Preservation and Restoration
Protecting and restoring flooded bottomland forest provides natural nest sites. Important tactics include:
- Preserve river floodplains, swamps, and biologically rich wetlands
- Allow controlled flooding cycles that regenerate snags
- Retain standing dead trees where safe to do so
- Reforest cleared areas with native flood-tolerant tree species
- Control invasive plants that outcompete native vegetation
- Mimic natural disturbance patterns like seasonal fires where appropriate
Combining nest boxes and habitat management provides the best long-term outlook for prothonotary warbler nesting success.
Conclusion
Prothonotary warblers showcase remarkable specificity in their nest-site requirements. They rely on flooded forests with dead snags over water to raise their young. Cavities in just the right trees, in just the right places enable their nesting success.
At the same time, they display adaptability to use diverse tree species and accept nest boxes when natural cavities are unavailable. Their flexibility combined with their strict habitat needs makes providing suitable nesting locations a complex but vital conservation challenge. Protecting remaining habitat and restoring degraded areas remains key to ensure the bright songbirds have nesting sites well into the future.