Bird nest July to September), it is not in others, and the swiftlets are declining in areas where the harvest reaches unsustainable levels. Some species of birds are also considered nuisances when they nest in the proximity of human habitations. Feral pigeons are often unwelcome and sometimes also considered as a health risk. The Beijing National Stadium, principal venue of the 2008 Summer Olympics, has been nicknamed "The Bird Nest" because of its architectural design, which its designers likened to a bird's woven nest. In the Victorian era, naturalists often collected bird's eggs and their nests. The study of bird nests is
Beijing National Stadium appearance, it was nicknamed "The Bird's Nest". The phrase was first used by Herzog & de Meuron, though the pair still believes "there should be many ways of perceiving a building." The use is a compliment Li explained, "In China, a bird's nest is very expensive, something you eat on special occasions." Construction of the stadium proceeded in several distinct phases, the first phase involving the construction of a concrete supporting structure upon the concrete foundations laid for the construction site. This was followed by the phased installation of the curved steel frame surrounding the stadium which is largely self-supporting.