The "cup nest" is probably the most common bird nest. Its name tells you that a cup nest is shaped like a cup or bowl. Many songbirds built cup nests. These nests can be built in the branches of a tree, like in the crack where one branch joins another: however, some can simply stick the nest right onto the branch of a tree. They use lots of materials that act like sticky glue – mud, rotten wood, dung, spider webs, and caterpillar silk. They sometimes even use their own saliva mixed with food to keep the nest firmly stuck on the branch.