This tower gives Chimney Swifts a place to nest and roost. Traditionally, these birds used large hollow trees. As large trees disappeared, they began to use chimneys. Now, modern chimneys are often capped or made of slick metal, making it impossible for the birds to build a nest. In spring, the swifts return from South America to breed. The nest is made of twigs glued to each other and to the interior wall using the bird's saliva. Both the male and female help to build the nest. Bristle-tipped tail feathers, and specialized feet allow the birds to cling to vertical surfaces.