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Cofrin Center for Biodiversity

The Science of Bird Eggs

Oology, is the branch of Ornithology specializing in the study of eggs. Because they are less expensive to prepare and curate, egg collections were once far more common than bird skin collections in museums. Scientific collectors realized that eggs were of value for more than their beauty or rarity. Bird eggs played important roles in describing new species and subspecies and in establishing taxonomic relationships among species. Collectors spent a great deal of time studying nesting habits and recording life histories of the species they encountered. Nearly all of our early, leading ornithologists were involved in egg collecting at some point in their careers. In many cases, important historical facts about bird distributions and bird ecology were first established by egg collectors. For example, in 1933 when Carl Richter collected an egg set of Bonaparte's Gull at Oconto, Wisconsin, he was asked to send the set to another collector in Alberta for verification. To this day, Richter's finding is the only documented breeding record for that species south of Canada (Robbins, Samuel D. 1991; Richter, Carl H. 1937).

Museum specimens are used by research biologists and conservation professionals to find historical records for nesting locations, preferred habitats, nest site selection and breeding phenology. Thanks to modern technology, egg shells also have become valuable indicators of environmental quality. During the 1960's, for example, biologists discovered that agricultural biocides and other pollutants, especially the chlorinated hydrocarbons, can affect calcium metabolism in birds (Hickey and Anderson 1968). Chemicals such as DDT, DDE and PCB's were shown to have deleterious effects on the calcification of eggs, leading to impaired reproduction in predatory species like Bald Eagle, Osprey, Peregrine, and Brown Pelican. Evidence for eggshell thinning came from comparisons of recently collected eggs with those in museum collections. Today museum egg shells can provide information about a wide variety of environmental contaminants as well as the genetic code (DNA) of the bird itself. Many egg shells from the Richter Collection were measured to demonstrate the shell thinning problem of the mid-1900's, which finally led to the banning of DDT in Wisconsin in 1971 and in the entire United States a year later. Eggs from highly exposed species such as gulls are now regularly collected to monitor pollutant levels in the Great Lakes ecosystem and to identify new contaminants before they become a threat to wildlife and humans.

Preparing an egg for a scientific collection

Eggshells are easiest to preserve when collected just after the entire clutch is laid and before incubation. The contents of collected eggs are carefully removed with a blowpipe through a single small hole. The shell is then cleaned, labeled and preserved.

Richter prepares an egg specimen.

Carl Richter removes the contents of an egg he is preparing for his collection.

Collecting wild bird eggs is now illegal except for specially authorized scientific research. Even permitted oological studies are rare today, although the Richter Museum's egg collection occasionally serves as a repository for authorized research projects or salvaged specimens.