Quantifying Past and Predicting Future Cumulative Loss of Habitat for a Critically Endangered Nomadic Bird

Abstract

Cumulative impacts occur through piecemeal habitat loss and are challenging to account for in planning decisions that are made on a case-by-case basis. Quantifying cumulative impacts is particularly difficult for nomadic species with large ranges, specific habitat requirements, and irregular movement patterns. We used a Geographic Information System approach to quantify past and predict future loss of important wintering habitat for the critically endangered swift parrot Lathamus discolor within the Hunter-Central Coast of New South Wales—an area of high importance to the species. Based on current NSW Government biodiversity assessment method (BAM) important habitat mapping, 717 ha of BAM important swift parrot habitat has been lost over the past two decades, representing 1.4% of the extent of important habitat in the Hunter-Central Coast. Over the next two decades, between 1.9% and 17.9% of current BAM important swift parrot habitat could be lost based on current planning data. Replacing the BAM mapping with a Maxent species distribution model, 10 081 ha of potentially important swift parrot habitat has been lost in the HCC over the past two decades, representing 1.71% of the current extent. Over the coming two decades, between 3289 and 19 643 ha of Maxent important swift parrot habitat could be lost, representing 2.4%–14.1% of the current area. The estimated loss is in addition to the severe loss that has already occurred in the Hunter-Central Coast and elsewhere within the swift parrot's winter range since European colonisation. Our study highlights the risks to threatened species of small-scale but sequential habitat loss, and how estimates of the extent of habitat loss vary depending how important habitat is defined. We discuss the implications of our findings for better considering cumulative impacts in planning processes and how to minimise the cumulative loss of important habitat for endangered species.