Cliff swallows are migratory birds that live in large colonies. This swallow is probably far more common today than when the Pilgrims landed. Originally it built its jug-shaped mud nests on the sides of cliffs. Cliff swallows, in other words, have proven to be marvelous animals for exploring the complexities involved in choosing where to live, a decision that millions of migratory birds are faced with annually upon their springtime return to the breeding grounds. Cliff swallows (Hirundo pyrrhonota) tend to be more of a problem for humans than their relatives the barn swallows. Barn swallows inhabit all areas of the world besides Australia and Antarctica. Those cliff swallows choosing small colonies may pay a more substantial cost of immigrating than those that choose large colonies. Colonies of cliff swallows (Aves: Hirundo pyrrhonota) appear to be information centers in which colony residents acquire information on the location of food sources. Cliff swallows are North American migratory birds. Bomberger Brown's bold conclusion is based on her 30-year study of cliff swallows – one of the longest running evolution studies in the world. Cliff Swallows have now been shown to have an unusually high degree of intraspecific brood parasitism, a phenomenon enhanced by the synchronized breeding within their colonies. Why do birds flock together? In Southwestern Nebraska, Cliff Swallow colonies contain up to 3,000 nests, making them … Taking advantage of these artificial locations, the species has invaded many areas where it never nested before. While they build the same clay nests that barn swallows do, they tend to nest in large colonies -- sometimes up to hundreds of pairs. However, the sides of barns and the supports of bridges provided sheltered sites that were far more widespread than the natural ones. Photo credit: Mary Bomberger Brown.