Architects of The Air

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Published on: Mar. 2, 1999

Last revision: Nov. 3, 2010

of our structures provide them with ideal nesting habitat. Their nests are a variation of the cup nest.

Barn swallows build their nests of mud pellets. Both parents deliver the pellets in their beaks to the nest site, which can be in barns, under bridges, on buildings and on cliffs. They construct a cone of mud and top it with a cup. Females then line the nests with softer materials, including feathers. Swallows commonly nest in colonies.

Chimney swifts construct an even more unusual variation of the cup nest. Swifts favor enclosed vertical spaces, such as chimneys, silos, old wells and attics for their nests. Both males and females will break twigs from the ends of dead branches to use for their nests. They stick the twigs to the wall with their own saliva, which soon hardens into glue. Eventually they accumulate a half-saucer nest for the eggs.

The cup is not the only design birds employ. Many species, including bald eagles, build a simple platform for their eggs. Both eagle partners pile branches, large sticks and even cornstalks in the fork of a tree, which is usually near water. They then line their platform with grasses and moss.

Bald eagles return and add new material to their nests year after year. Sometimes they build two nests, so they can alternate sites annually, which may reduce lice infestation. Some bald eagle nests have been used for up to 30 years, but often by this time they have grown so heavy from their annual accumulation of material that they crash to the earth under their own weight.

Most birds of prey build platform nests. Sometimes they build on cliff ledges, rather than in trees. American kestrels, typically cavity nesters, sometimes build their nests in the underparts of golden eagle nests. Grackles sometimes do the same in osprey nests.

Great blue herons are platform builders and generally nest in colonies. The male brings the sticks to the female and she arranges them on the nest, usually in the highest part of the tree. Mourning doves also build platform nests, sometimes on top of abandoned robin nests. Mourning dove nests are often insubstantial, and the eggs in them may be visible from below.

Woodpeckers meet the nesting challenge by gouging cavities in the trunks of dead trees. Commonly, that's the extent of the nest, though they may soften it with wood chips in the bottom. The entrance to the pileated

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