In the U.S., some birds, mostly members of the swallow family, build mud nests. The birds skillfully combine mud and dirt with their own saliva to construct a sturdy place to live and lay their eggs.
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.
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.
The most widely distributed swallow in the world, the barn swallow often will build its mud nest in barns, sheds, garages and outbuilding.
The purple martin is the largest of the American swallows. 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.
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.