Nest building is, in a way, a more advanced version of choosing the best microclimate. An animal seeking out a rock crevice or hole in the earth as a place to rest and be cool is indeed seeking out a favorable microclimate. Digging the hole a little deeper and adding a bit of shed fur for insulation are simple improvements. All animals start their nests by finding the best location and only a few of the most talented nest builders- such as some birds, beavers, and Horno sapiens-can completely transform an environment to meet their nesting needs. The Anasazi Indians of the southwestern United States were remarkably clever in choosing the sites for their cliff dwellings. They invariably chose locations shaded in the summer by an overhanging ledge of the cliff, but exposed to full sun all winter long. With their backs to the cliff, the dwellings were protected from the winter winds and also took advantage of the thermal mass of the earth to moderate the temperature flux.