Bird houses are structures that provide shelter and protection for birds. They can be made from a variety of materials, such as wood, metal, or plastic. The most common type of bird house is a nest, which is typically made from twigs and other natural materials. Tree houses are also popular bird houses, and they are usually built in the branches of trees. Igloos are another type of bird house, and they are made from blocks of snow and ice. All of these bird houses provide a safe and comfortable home for birds.