Generalized Mark-Sight Population Size Estimation Applied to Colorado Moose

A new procedure for constructing confidence interval estimates of population size in mark-sight experiments is presented. The method of selecting animals for marking must be equivalent to a simple random sample without replacement. Marked animals are required to be individually identifiable. The number of times animals are sighted must be independent of their mark status. The sighting process does not need to be composed of independent sighting trials or even decomposable into separate trials. Sighting probabilities can vary among individuals and can depend on such factors as group size and vegetational cover. Other methods of constructing confidence intervals in mark-sight experiments given these latter conditions have failed to achieve their stated nominal confidence level. Our confidence interval procedures are shown by simulation to have actual confidence levels close to nominal under conditions encountered in an application to a Colorado moose (Alces alces shirasi) population. For this population with 29 radio-collared moose and 5 helicopter sighting flights, the 90% confidence interval for the moose population size on the 1,400-km 2 area was 382-505.