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
Parental care in birds and amount of care provided. With an increase in available mates in some birds (such as the rock sparrow), female desertion rate increases leading to more mono-parental care. When female rock sparrows were exposed to an abundant amount of male mates approximately 50% of the females deserted their first nest when the hatchlings were on average 14.3 days old. The fathers successfully took over all parental duties (Pilastro). Female birds are able to produce more of a certain gender of birds that are more likely to survive under extreme conditions. In birds, the females' egg determines the gender of the