As I mentioned earlier, cliff swallows (Petrochlidon pyrrhonota) construct gourd-shaped nests on vertical walls. No reinforcing material is added to the mud pellets that comprise the nest. A small entrance tunnel gives access to these completely enclosed swallow nests that are lined with feathers and grass.
Although cliff swallows will occasionally build solitary nests, usually these birds form large breeding colonies. I find their nesting habits a little unusual. Although cliff swallow pairs are monogamous, females will lay eggs in the nests of other colony members. Even after a female lays an egg in her own nest, she will sometimes take an egg in her bill and transfer it to another nest. (I have a difficult time visualizing a cliff swallow with her small bill carrying an egg to a nearby nest.) Thus chicks of different parentage can be found in any one nest. I wonder why cliff swallows put their eggs in the nests of other females? Unlike cowbirds that relieve themselves of the work of raising a brood by laying eggs in other birds’ nests, cliff swallows incubate the eggs and raise the chicks. Perhaps this strategy assures that if any particular nest is destroyed, some of a cliff swallow’s progeny might still survive – not putting all one’s eggs in one basket, so to speak.
Fledged cliff swallows congregate together in large groups called creches. After fledging the parents continue to feed their young for three to five days after they leave the nest. Parents recognize their offspring in the creche by voice, and perhaps by fine distinctions in plumage.
These nests are located on the Hat Creek Hydroelectric Plant #1 in Shasta County Ca. At the time the pictures were taken the cliff swallows appeared to be repairing nests from last season. As you can see, a few of the nests need extensive work to become habitable again. The other pictures are cliff swallows collecting mud pellets along the bank of Hat Creek.