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 many as 300 mating pairs may reside in the structure. Other birds often built their own nests on top of Weaver nest sites. Some birds build nests in trees, some (such as vultures, eagles, and many seabirds) will build them on rocky ledges, and others nest on the ground or in burrows. Each species has a characteristic nest style, but few are particular about where they build their nests. Most species will choose whatever site in their environment best protects their nest, taking into account the nest's style. Several species will build on a cactus whenever possible. The bushtit and