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 do not directly brood their young, incubate their young in a mound of decomposing vegetation. One species, "Macrocephalon maleo", uses volcanic sand warmed by geothermal heat to keep its eggs warm. Among the simple nest builders are falcons, owls, and many shorebirds. The weavers exhibit perhaps the most elaborate nests, complete with strands of grass tied into knots. Most bird nests lie somewhere in the middle, with the majority building cup-shaped nests using some combination of mud, twigs and leaves, and feathers. Some birds, such flamingos and swifts, use saliva to help hold their nest together. The edible-nest swiftlet uses