Index Numbers for Waterbird Populations. I. Review and Methodology

Abstract

This paper reviews methods used to estimate bird population index numbers and proposes a new method. An index number for a year is defined as the ratio of the population size in the year to the population size in the base year. In the context of waterbird populations, the major problem with generating index numbers is the fact that, owing to missing observations at a subset of localities, the total population size in any year is unknown. We suggest a model-based approach to imputing missing observations so that the total population size at the localities may be estimated and used to produce a series of index numbers of the population sizes each year