Lichen as bird’s nest camouflage – Waterbury Roundabout


Birds use a wonderful variety of materials and techniques to create their nests.

Some nests are small and tidy like baskets of grass lined with cozy feathers. Others are large and stained with mud. Some species build their nests in trees, some on the ground, and others woven into wetland plants or stuck to cliff faces – or your back porch wall.

I have spotted and admired many bird nests, but never one made by a ruby-throated hummingbird or a blue-grey gnatcatcher. This is likely due to both species covering their nests with lichens, making them exceptionally well camouflaged.

Ruby-throated hummingbirds and blue-grey midges breed in the northeast, arriving and beginning their nesting in early spring, according to Robyn Bailey, NestWatch project manager at the Cornell Lab of Ornithology.

While many birds incorporate lichens into their nests, researchers believe that hummingbirds and gnatcatchers use lichens every time. Bailey cited a 2010 study from Ohio in which “every published nest description mentions the presence of lichens as exterior shingles on midge and hummingbird nests.”

Hummingbird nests are very small, about 2 inches wide and 1 inch high, and fashioned from thistle and dandelion glued together with spider silk or pine resin. Midge nests are slightly larger, up to 3 inches wide, and are built in layers. The first structural layer is woven from fibrous materials such as stems, bark and grass, with each layer incorporating finer materials through to the inner cap layer, which is lined with soft materials including plant down, cocoons, hair or feathers.

Both species attach their nests firmly to the tops of thin, horizontal branches. The birds use spider silk to coat the outside of the nest and the supporting branch with lichens, fusing the silhouette of the nest with the outlines of the branch. Unless you look directly at the eggs inside, one of these nests looks like a lichen-encrusted knot.

Hummingbirds and gnatcatchers are pragmatic about their choices of lichens. They scoop up nesting materials with their beaks while hovering in the air, Bailey said. Therefore, they prefer the common foliose (leaf) lichens that grow on trees, with fatty lobes that attach loosely to the bark and are easy to grab by the beak.

In a survey of nests, Ohio researchers found that hummingbirds and gnatcatchers preferred lichen species, including hammerhead shield lichen (Parmelia sulcata), two speckled shield lichens (Punctelia spp.) and green shield lichen (Flavoparmelia caperata). All of these lichens tend to form round, doily-like spots on trees that range in color from powdery gray to washed out cyan to pale green.

Sourcing materials is a challenge for all nest-building birds. If they prefer or need hard-to-find material, it could reduce their ability to build a successful nest.

Bailey thinks hummingbirds and gnatcatchers rarely, if ever, have trouble finding lichens in northern forests. Both nest in lichen-encrusted habitats. However, Ohio researchers believe air pollution could be impacting these birds through the lichens they harvest. Some of the lichen species that hummingbirds commonly use in their nests, including a speckled shield lichen and the green shield lichen, are sensitive to air quality, leading researchers to raise the possibility that ” increased air pollution may adversely affect blue nesting success. – gray gnatcatchers and ruby-throated hummingbirds.

Hummingbird and gnatcatcher nests are rarely reused, although birds may nest twice in a single breeding season. “Nests get dirty and predators find them,” Bailey said, and most nests collapse during the winter before the birds return. However, birds sometimes reuse materials from the first nest to make a second one during the same breeding season.

Although the nests themselves are ephemeral, their impact on lichens may not be. A preliminary study from Virginia found that hummingbirds tend to place nesting lichens where they might survive or even thrive. Researchers have found that lichens can persist for at least three years after being incorporated into a nest, giving lichens the chance to grow on the branch where the nest was built and suggesting that birds could help their favorite lichens to spread to new homes. .

Given their effective camouflage, I wouldn’t expect to stumble upon a ruby-throated hummingbird or blue-grey gnatcatcher’s nest, but I can look for familiar lichens on the trees I pass and imagine how they might appear as pebbles on a small nest.

Rachel Sargent Mirus lives in Duxbury, Vermont. Exterior story is assigned and edited by Northern forests magazine and sponsored by the Wellborn Ecology Fund of the New Hampshire Charitable Foundation.


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