Cliff Swallows 🪶

by Dr. Oakleigh Thorne, II

Cliff Swallow nest and male roosting platform.



For many years I have been doing research on the Cliff Swallow (Petrochelidon pyrrhonota). This is my favorite kind of bird. Cliff Swallows traditionally nest in great numbers under overhanging sandstone cliffs along many of our major Western rivers. After settlers came to the West, however, they built bridges and road culverts (where streams flow under highways or railroad tracks). Cliff Swallows found these new structures great for their nesting sites, so throughout Boulder County there are many being used by these birds.


Cliff Swallows are colonial nesters, which means that they usually build their nests right next to each other in a colony. They therefore tolerate other swallows right next to them, unlike other kinds of birds that have and defend much larger nesting territories.


Cliff Swallows construct their nests out of little balls of mud mixed with their saliva that they stick together, one by one, attached to the rough cement inside the culvert. The finished nests look like mud beehives all in a row along the upper corners of the culvert.


I have a Federal Master Bird Banding permit from the U.S. Department of the Interior. I catch Cliff Swallows using a mist net, a soft net stretched between two metal poles. With the help of students from my Birds and Bird Banding class at Thorne Nature Experience, we drop this across the opening of a typical culvert and catch many birds at one time as they fly out.


Our students learn to carefully remove the swallows from the net. Then they open the numbered bands with special pliers and place one of these around the leg of each bird, closing the band so that it creates a small “bracelet” that the swallow wears for the rest of its life. Each band has its own special number so we can always tell which bird is which.


Swallows eat flying insects, so they are always feeding by flying around and catching gnats, mosquitoes, and various kinds of bugs in midair. You will sometimes see them flying through busy street intersections where the carbon dioxide from cars may be attracting the insects. Because their diet depends on flying insects, swallows must migrate south to where there is “perpetual summer,” far away from our bug-less winters.


Cliff Swallows migrate all the way to southern Brazil and Argentina. So when we recapture one of our banded birds the following summer, we know that it has traveled all the way to South America and back since we banded it. That’s nearly 12,000 miles. But since Cliff Swallows feed while they migrate, swooping back and forth, I estimate that they fly perhaps as many as 80,000 miles per year! These “returns,” as we call them, are exciting to get. Banding can help us tell how many swallows survive this amazing round-trip.


We banded an adult Cliff Swallow in 1996 that we caught again in 2006, which proved it was at least eleven years old, flying perhaps a million miles in its lifetime! These population studies are the main part of our research. I hope you can join our Bird Banding class someday.


Dr. Thorne is founder and honorary president of Thorne Nature Experience (formerly Thorne Ecological Institute), in Boulder. For more information about their summer camps for children, please check www.thornenature.org or e-mail info@thornenature.org or call (303) 499-3647.

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