Managing the long-term persistence of a rare cockatoo under climate change

Abstract

1. Linked demographic-bioclimatic models are emerging tools for forecasting climate change impacts on well-studied species, but these methods have been used in few management applications, and species interactions have not been incorporated. We combined population and bioclimatic envelope models to estimate future risks to the viability of a cockatoo population posed by climate change, increased fire frequency, beak-and-feather disease and reduced management. 2. The South Australian glossy black-cockatoo Calyptorhynchus lathami halmaturinus is restricted to Kangaroo Island, Australia, where it numbers 350 birds and is managed intensively. The cockatoo may be at particular risk from climate change because of its insular geographic constraints and specialised diet on a single plant species, Allocasuarina verticillata. The cockatoo population model was parameterised with mark-resight-derived estimates of survival and fecundity from 13 years of demographic data. Species interactions were incorporated by using a climate-change-driven bioclimatic model of Allocasuarina verticillata as a dynamic driver of habitat suitability. A novel application of Latin Hypercube sampling was used to assess the model’s sensitivity to input parameters. 3. Results suggest that unmitigated climate change is likely to be a substantial threat for the cockatoo: all high-CO2-concentration scenarios had expected minimum abundances of <160 birds. Extinction was virtually certain if management of nest-predating brush-tail possums Trichosurus vulpecula was stopped, or adult survival reduced by as little as 5%. In contrast, the population is predicted to increase under low-emissions scenarios. 4. Disease outbreak, increased fire frequency and reductions in revegetation and management of competitive little corellas Cacatua sanguinea, were all predicted to exacerbate decline, but these effects were buffered by the cockatoo population’s high fecundity. 5. Spatial correlates of extinction risk, such as range area and total habitat suitability, were nonlinearly related to projected population size in the high-CO2-concentration scenario. 6. Synthesis and applications. Mechanistic demographic-bioclimatic simulations that incorporate species interactions can provide more detailed viability analyses than traditional bioclimatic models and be used to rank the cost-effectiveness of management interventions. Our results highlight the importance of managing possum predation and maintaining high adult cockatoo survival. In contrast, corella and revegetation management could be experimentally reduced to save resources.