Abnormal eggs of the Common Guillemot Uria aalge: the role of stress

This study documents several types of abnormal eggs of the Common Guillemot Uria aalge collected from Bempton Cliffs, Yorkshire, UK, during the 1900s and currently housed in the Natural History Museum at Tring, Hertfordshire, UK. These eggs are abnormal in terms of size, shape, colour and surface topography. We suggest that the incidence of these abnormal eggs was relatively high because the manner in which they were collected — repeated visits to the breeding colony — caused considerable disturbance and stress that in turn disrupted the normal process of egg formation. We discuss the possibility of using abnormalities in avian eggs as a measurement of environmental stress.