Although point counts are frequently used in ornithological studies, basic assumptions about consistency in detection probabilities often remain untested. The secondary observer records all detections of the primary observer, as well as any birds not detected by the primary observer.
Observers alternate primary and secondary roles during the course of a survey.
The approach permits estimation of observer-specific detection probabilities and bird abundance. Single observer point counts generally miss varying proportions of the birds actually present, as observer and bird species were both found to be relevant sources of variation in detection probabilities. We believe that most questions meriting the effort required to carry out point counts also merit serious attempts to estimate detection probabilities associated with the counts. The double-observer approach is a method which can be used for this purpose. Models Estimates for detection probability are generated under several models.