Birds are a hot topic in the design world. More specifically city birds. A typical design project are these great bird house roof tiles by Klaas Kuiken, that tend to provide an esthetical, yet subtle solution to accommodate city birds. The roof tiles are made of terracotta with a small house perched on top where the bird can nest in. A similar design are the so-called Bird Bricks: built-in, customized nests for endangered species like the house martin, spotted flycatcher and the house sparrow. The bricks can be set into the walls of a house. According to designer Fanny Hofstra the city birds will return every year once they nest somewhere into the walls.