Geographic patterns and correlates of the decline of granivorous birds in northern Australia
Donald C. Franklin A G , Peter J. Whitehead A B , Guy Pardon A C , Janet Matthews A D , Philip McMahon A E and Daniel McIntyre A FA School for Environmental Research, Charles Darwin University, Darwin, NT 0909, Australia.
B Current address: Department of Infrastructure Planning and Environment, PO Box 496, Palmerston, NT 0831, Australia.
C Current address: 5/56 Chapman Road, Rapid Creek, NT 0810, Australia.
D Current address: 84 Carnoustie Circuit, Northlakes, NT 0812, Australia.
E Current address: PO Box 390, Howard Springs, NT 0835, Australia.
F Current address: Department of Spatial Sciences, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia.
G Corresponding author: Email: don.franklin@cdu.edu.au
Wildlife Research 32(5) 399-408 https://doi.org/10.1071/WR05052
Submitted: 27 May 2005 Accepted: 28 June 2005 Published: 8 August 2005
Abstract
A geographic index of the decline in the distribution and abundance of granivorous birds in tropical northern Australia shows that declines are greatest in Queensland and especially in the south-eastern tropics and in inland areas, and lowest in the north Kimberley and east Arnhem districts. In this paper, we use generalised linear models to investigate interrelationships among an index of decline in 1° by 1° cells and measures of grazing intensity and contemporary patterns of burning, together with the environmental variables of rainfall, vegetation and topographic patterning in the landscape. Grazing intensity was the single strongest human effect but strong correlations between grazing intensity and other human influences suggest that these may have been subsumed within the grazing intensity measure. Impacts of grazing may be worse where pastoral settlement occurred earlier. Topographic variation appeared to be a mitigating effect, suggesting a role for ‘topographic refuges’ from human activities. Relationships among granivore declines, grazing and rainfall are difficult to disentangle using inferential statistics, but a consistent effect is that declines are more severe in areas with greater year-to-year variation in rainfall. We do not suggest that our analyses are conclusive. However, they do support the proposition that better understanding of the causes of decline at finer spatial scales will emerge most strongly in studies that link habitat quality with granivore demography at inland sites of highly variable year-to-year rainfall and with strongly contrasting grazing histories.
Acknowledgments
Compilation of the historic dataset and derivation of the index of decline was undertaken while the senior author was funded and supported by the Tropical Savannas CRC, the Gouldian Finch Recovery Project and the Parks and Wildlife Commission NT. We are grateful to Andrew Edwards for making digital data available for these analyses. Our ideas about the decline of granivorous birds have benefited from extensive discussion with many people, particularly John Woinarski and Stephen Garnett.
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