“Oology” combines “oo-,” a Greek word-forming element meaning “egg,” and “-logy,” a suffix that indicates a field of study. Any casual bird-watcher can practice oology (although observing is better practice than collecting wild bird eggs), but it’s also a scientific field with practical application. In the 1960s, British naturalist and oologist Derek Ratcliffe compared peregrine falcon eggs from historical collections with more recent eggshells and was able to determine a decline in shell thickness over time. This helped establish a link between the declining British populations of birds of prey and the use of pesticides and insecticides.