Natural Wooden/Bark Bird Nesting Box/House The 30mm hole and the size of the box are suitable for a variety of small birds to nest inside roost in the winter. In rural areas, there is a huge shortage of safe natural nesting places for birds. We can all help with this by putting up nesting boxes and encouraging them to breed near your home. Cats are another huge problem for wildlife, recent figures say that cats in the UK catch up to 100 million prey items over spring and summer, of which 27 million are birds. Keep this in mind when placing the birdbox. Specification Material: Pine and Acetate. Dimensions: 16 x 14 x 20cm. Wooden bird nesting box.