A Double-Survey Estimate of Population Size from Incomplete Counts

We sought to estimate the number of crocodile nests on the Liverpool River, Northern Territory, Australia. Two methods of survey were available, aerial survey and ground survey, in each of which sightings could be mapped. Hence, those nests which were detected by both methods could be identified. These counts were used to demonstrate the method by which an estimate of total number could be calculated. The assumptions and limitations are discussed.