<P> 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 . </P> <P> 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 . </P> <P> In the Victorian era, naturalists often collected bird's eggs and their nests . The study of bird nests is called caliology . </P> <P> Bird nests are also built by humans to help in the conservation of certain birds (such as swallows). Swallow nests are generally built with plaster, wood, terracotta or stucco . </P>

Different types of birds and their nests in hindi