Estimating Uncertainty in Wildlife Population Estimates
Estimating an index of animal population size from simple counts can be very challenging. If indices are to be compared among years to assess trend there must be some consistency in what fraction of the population the index is measuring. Variation in population indices among years may be due to variation in the size of the population but it may also be due to variation in counting procedure, in animal detection and, for migratory and foraging animals, in the proportion of the total population available to be counted. We discuss two case-studies of animal counts where we attempt to quantify this extra variation, or uncertainty, using Monte Carlo simulation. In the first case-study we assess uncertainty in penguin population indices from counts, and in the second, we assess uncertainty in migratory bird counts from braided rivers in New Zealand.