A comparison of two methods for surveying mortality of beached birds in British Columbia

Systematic surveys of beached birds are often limited in their ability to classify the causes of death of the carcasses recovered. Two methods of determining the cause of death of seabirds encountered during surveys of beaches of southwestern Vancouver Island, British Columbia, are compared. Birds were either subjected to external visual examinations by volunteer beach surveyors or submitted for gross postmortem examination by a veterinarian. The reliance on external examination of birds on beaches often prevented the accurate classification of the reproductive status and cause of death of the birds collected, but was valuable for describing the species, locations, and numbers of birds affected. The use of gross postmortem examinations of carcasses allowed for a more refined classification of the cause of death, as well as providing reliable descriptions of the bodily condition and sex of the birds examined. However, almost one half of the carcasses encountered were unsuitable for necropsy because of scavenging and decomposition. It is concluded that a combination of field and necropsy observations provides a useful method with which to monitor the pattern of mortality of beached seabirds.