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
Capital city of Australia are Adelaide; Brisbane; Hobart; Melbourne; Perth; and Sydney. In Australia, the term "capital cities" is regularly used to refer to the aforementioned state capitals plus the federal capital Canberra and Darwin, the capital of the Northern Territory. Abu Dhabi is the capital city of the Emirate of Abu Dhabi and the United Arab Emirates overall. In unitary states which consist of multiple constituent nations, such as the United Kingdom or the Kingdom of Denmark, each will usually have its own capital city. Unlike in federations, there is usually not a separate national capital, but rather the capital city