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Earth Notes: Cliff Swallow Nests

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U.S. Geological Survey
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Cliff swallow nests

In the fall, large flocks of cliff swallows take wing together, heading all the way to South America to overwinter. But they’ll be back in the spring, ready to breed and claim nesting sites.

Down most any canyon or river in the Southwest, you’ll likely spot their distinctive nests. The gourd-shaped structures are the work of master builders. Each is made of mud pellets that the swallows scoop up in their beaks, one by one, and lay up in a methodical way—first the floor, then sides, then roof, leaving a small entryway. The nests are plastered onto cliff faces, usually under an overhang.

These are social birds that prefer high-density housing. A colony may contain hundreds of individual swallows. They’ll get a little aggressive against the competition when vying for a favored nest site, and will staunchly defend the hard-fought spot.

After choosing a suitable location, the pair works in tandem to build a nest, lining it with soft feathers and grass. Or, they may choose a fixer-upper and reuse it.

The female lays three to six eggs inside the cozy home, then both parents will incubate them. Hatchlings appear in a couple weeks, and hungrily feed on insects for about a month before departing the nest.

Cliff swallows range from Alaska to Mexico and across most of the U.S., and have readily adapted to human presence. They’ll select bridges, buildings, culverts--most any vertical surface--with mud nearby for nests. That flexibility has allowed them to gain more habitat and extend their range farther north and east—a success story for a hard-working bird.

This Earth Note was written by Rose Houk and produced by KNAU and the Sustainable Communities Program at Northern Arizona University.

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