Oology
![Mid-19th century illustration showing the eggs of a number of different bird species](/Images/godic/202501/31/Bird_eggs4058.jpg")
Oology (or oölogy) is a branch of ornithology studying bird eggs, nests and breeding behaviour. The word is derived from the Greek "oion", meaning egg. Oology can also refer to the hobby of collecting wild birds' eggs, sometimes called egg collecting, birdnesting or egging, which is now illegal in many jurisdictions.