Using re-sighting data to estimate population size of Pink-footed Geese (Anser brachyrhynchus)

Abstract

In wildlife management, the ability to reliably assess population sizes is a basic prerequisite. When populations are managed specifically to maintain a population target this is even more vital. In this study we apply a mark-resight approach using neck-collared geese to develop and present an alternative method to total counts when estimating the population size of Pink-footed Geese (Anser brachyrhynchus). Estimates of population size from the mark-resight approach showed an increasing trend from 31,000 birds in 1991/ 1992 to 100,700 birds in 2011/2012, and fluctuating numbers around 80,000 in recent years. By exploring the relationship between uncertainty of the population estimate and the monitoring effort, we showed that a minimum of approximately 120 independent flocks greater than 100 birds should be surveyed to derive a ratio estimate of marked to unmarked birds minimizing uncertainty of the overall population estimate.