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These birds are also known as mud swallows and are of the hirundo pyrrhonata species. They spend their winters in South America and typically migrate northward to the United States annually from March to June.

They are known as mud swallows because they build nests of mud. These are usually built beneath an overhang or eave and typically against a vertical wall. The nests are usually 6 inches in diameter and shaped like gourds with necklike entrance ways with round holes. Birds can be seen flying in and out of the nests in spring and the area beneath the nests will often be covered with bird and mud droppings.

When the cliff swallows migrate to the United States they form their mud houses and if left untouched they will use the same nesting sites year after year. Even if the same specific site is not used the following year, birds tend to migrate to the same general location year after year. Nests are abandoned by the end of June.

When you see mud nests, you will need to contact the U.S. Fish and Wildlife Service prior to removing them. Swallows are protected by both state and federal regulations and you may need a depredation permit. Once these steps have been taken you can wash the nests from under eaves with a strong jet of water. You must do this consistently over a long period of time or the birds will continue to return until they have created a mud colony. Another means of preventing re-mudding the following year is to string a wire across the area where the nest was and drape a footlong curtain of aluminum foil which will prevent birds from attaching mud to the walls. Cliff swallows are tenacious, and if all else fails you may need to contact a licensed professional for mud nest removal.