Chimney swifts in a chimney

As you look closely into this chimney, you can see a chimney swift nest. These swifts built a nest from twigs and used their own saliva to attach it to the inner wall of the chimney. True to their name, chimney swifts nest individually in masonry chimneys and other human-made structures, such as barns, silos, and vents. They cling vertically to the sides of these structures, which are made of brick, stone, mortar, or other material that has a rough, porous texture. That texture helps them cling easier.