"Oology" is the study of birds' egg or eggs in general. It can also refer to the hobby of collecting eggs of birds. Just like the varieties in nests, birds show a wide array of variants in egg structure. This biological term is different from "Nidology" which is the study of nests. In short , the collection and study of eggs in relation to their shape and coloration is called "Oology". The word is derived from the Greek word 'oion' meaning egg.

Oology became increasingly popular in Britain and the United States during the 1800s, when observing birds from afar was difficult due to lack of high quality binoculars. In the 1960s, the naturalists Derek Ratcliffe compared peregrine falcon eggs from historical collections with more recent egg-shell samples, and was able to demonstrate a decline in shell thickness. This was found to cause the link between the use by farmers of pesticides and decline of bird prey.

In 1922, the British Oological Association was founded by Baron Rothschild, a prominent naturalist and it was later on renamed as the Jourdain Society.

It is a branch of ornithology or Zoology, concerned more with the scientific study of bird's eggs rather than a egg-collection hobby.

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