A bir nest is the spot in which a bird lays and incubates its eggs and raises its young. While the term popularly refers to a specific structure made by the bird itself—such as the grassy cup nest of the American Robin or Eurasian Blackbird, or the elaborately woven hanging nest of the Montezuma Oropendola, the Village Weaver or the Red-browed Pardalote—that is too restrictive a definition. For some species, a nest is simply a shallow depression made in sand; for others, it is the knot-hole left by a broken branch, a burrow dug into the ground, a chamber drilled into a tree, an enormous rotting pile of vegetation and earth, or a mud dome with an entrance tunnel. Some species of cave swiftlets of the genus Collocalia make their nests entirely from their saliva, which dries and hardens to form a bracket on the cave wall into which the birds lay their eggs.