Revising estimates of the Shoebill (Balaeniceps rex) population size in the Bangweulu Swamp, Zambia, through a combination of aerial surveys and habitat suitability modelling

Abstract

The Shoebill Balaeniceps rex is a threatened bird of inaccessible papyrus swamps in central and eastern Africa, and is thus difficult to census. We conducted an aerial survey of Shoebills in the Bangweulu Swamps of north-eastern Zambia using a microlight aircraft in July 2006, and used strip transect methodology to estimate population size. We then applied maximum entropy modelling to satellite images to produce a quantitative map of the likelihood of habitat being suitable (occupied), based on the location of Shoebill sightings. Population size was then re-estimated based on the extent of potentially suitable habitat, which covered 37% of the swamp. Our most conservative mean population size estimate of 1 296 individuals is 550% higher than previous estimates. We suggest that previous estimates may have been underestimates. Our study provides the first estimate of the extent of potentially suitable habitat and an estimate of the population size of Shoebills for the entire swamp. Our analysis of potential habitat suitability can be used to guide future Shoebill surveys, and our methodology can be applied to other little known and inaccessible sites to improve estimates of population size continent-wide.