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
Nest fecal matter, and specialized secretions from the animal's body. Nest building can have a substantial impact on the environment in which animals live. The combined digging activity of termites and mole-rats in South Africa has created a "mima prairie" landscape marked by huge areas of flat land punctuated by mounds wide and high. Similar structures exist in the United States, created by pocket gophers, and Argentina, rodents of the genus "Ctenomys". Nests constructed by megapode birds have been mistaken for anthropological features by professionals, due to their exceptional height () and abundance (hundreds in a single location). Nest architecture may