A bird's home can be a NEST, a CAGE, a tree, or a HANGAR. A NEST is a structure made of twigs and other materials that birds build to lay their eggs in and raise their young. A CAGE is an enclosure made of metal bars or wire mesh used to keep birds confined. A tree is a tall plant with a trunk and branches that provides shelter for birds. A HANGAR is a large building used to store aircraft, but it can also provide shelter for some types of birds.