Collecting Mud

Cliff swallows (Petrochelidon pyrrhonota) historically built their nests on cliff faces or escarpments throughout large portions of North America. Now these social birds also use overpasses, buildings, bridges or other man-made structures for their nests, anywhere there is a juncture of a vertical wall and a horizontal overhang. Occasionally cliff swallows will build a solitary nest, however, they usually form large colonies that can number in the hundreds of nests.

Cliff swallow nests are gourd-shaped structures built entirely of mud and saliva. The entrance is an elongated tube. The mud shell is lined with dry grasses. Although the male may begin building a nest before attracting a female, both partners work to finish the nest. Cliff swallows collect mud pellets, usually from nearby wet areas, and shape them into place to form the nest. A completed nest contains 900-1,200 individual pellets.  Nests are often reused year after year with “remodeling” to repair damage incurred over the winter. Cliff swallows sleep in trees most of the year, but will begin to sleep in a nest before it is finished and throughout the breeding season.

The female lays 1 to 6 white or pinkish eggs with brown speckles. She will also lay eggs in nearby nests or will move an egg from her nest into a neighboring nest. Although they place eggs in other swallow nests, cliff swallows care for the eggs in their nest. A pair of cliff swallows will raise the young in their nest together, but both members of a pair will also mate outside the pair bond. Helpless chicks with bare pink skin hatch after 10 to 19 days of incubation. Feldging occurs after 20 to 26 days.

Driving along County Road 91 near Lookout CA (Modoc County) Leonard and I saw about fifty cliff swallows atop the muddy, swampy ground. They almost resembled a swarm of bees picking at the soil and flying to and fro. We briefly wondered what the swallows were doing, then remembered that this is an area where hundreds of cliff swallows build nests below a low bridge. The swallows were collecting mud pellets and constructing (or repairing) their nests. It looks to be a good summer for cliff swallows.

The pictured cliff swallow nests were photographed several years ago along Hat Creek (Shasta County CA) where where the swallows raised their broods under the eaves of Hydroelectric Plant #1.

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