Cliff Swallow (pictured above)
The cliff swallow constructs a bowl-shaped nest made of mud pellets on a vertical wall, typically beneath some sort of overhang. The bird lines the nest with grass to make it more comfortable and warm. A finished nest will contain over 1,000 mud pellets. Cliff swallows nest in colonies that can contain hundreds or thousands of birds.
The cave swallow, which lives in portions of Florida and Texas, builds a nest similar to the cliff swallow. These elaborate nests are sometimes covered and have a tunnel leading to them, which is made of mud. As their name indicates, cave swallows often nest inside the entrances to caves. To get a good look at a cave swallow, visit Carlsbad Caverns in New Mexico.
The most widely distributed swallow in the world, the barn swallow often will build its mud nest in barns, sheds, garages and outbuildings. This beautiful cobalt blue bird can be identified by the fork in its tail and by the cup-shaped mud nests that they build exclusively on man-made structures.
The purple martin is the largest of the American swallows. Native Americans used to hang up empty gourds for the bird to nest in, but now it lives almost exclusively in birdhouses provided by people in the eastern U.S. In these boxes, it will make a nest of mud, grass and twigs.
Found in western North America, black-billed magpies are noisy birds that can often be found perched atop fenceposts or in the tops of trees. The birds build very large domed nests in trees that can take up to 40 days to build. The exterior of the nests are made of sticks and the interior is a mud cup lined with grass.
The flamingo's nest is a cone shaped mound of mud one or two feet high and a foot across. A shallow depression on the top of the mound holds the flamingo's eggs. Female flamingos lay one solitary egg which is protected by both parents for 30 days until the egg is hatched. (Pictured below: Colony of Caribbean flamingos on their nests. Rio Maximo, Camaguey, Cuba)