Assessing the value of wetlands to waterbirds: exploring a population-based index at flyway and regional levels

Traditionally, species richness, species diversity, total count, biomass, energy consumption and the Ramsar '1% threshold' have been used to assess the importance of wetlands for waterbirds. Designation of wetlands of international importance (Ramsar sites) based on waterbirds has focused on those species meeting the Ramsar 1% population threshold levels. These levels prioritise a subset of species as being important, with little or no consideration to the contributions of the remaining species' populations. In this paper, we evaluate and further describe a quantitative method to assess wetland avifaunal importance. Termed the Waterbird Conservation Value (WCV), this index sums the ratio of each species' abundance to its published 1% threshold across all species to give an overall measure of the 'value' of the waterbirds at a wetland. Large values indicate that large proportions of the total populations of waterbird species are present at the wetland. Indices can be evaluated at site and species levels. The WCV is a more nuanced approach, sensitive to actual species' abundance rather than counts of '1% threshold' species and considers all species in the assessment. The outputs of the WCV index are demonstrated and discussed using a case study from three regions within the East Atlantic flyway.