According to this article a 2,500 bird’s nest has been found on a cliff in Greenland. The nesting site is used by gyrfalcons and includes three other nests all of which are more than 1,000 years old. Ornithologists discovered how old the nests were when they were trying to find out long the birds return to the same site. They used carbon to date the bird droppings and debris left behind and were surprised to find out how the nests actually were. One of the nests also contains feathers from a bird which would have lived more than 600 years ago.