PARENT SESSION
Oral Session #24: Conservation and Biodiversity: Birds and arthropods.
Presiding: C. Bock
Monday, August 5. 1:00 PM to 3:45 PM. Mesquite Room, Radisson.
Change in bird populations in the Australian arid zone over 25 years.
MELBOURNE, BRETT*,1,3, DAVIES, KENDI1,3, CUNNINGHAM, ROSS2, JAMES, CRAIG3, GRIFFIN, GRAHAM3, 1 University of California, Davis3 CSIRO Centre for Arid Zone Research, Alice Springs, Australia2 Australian National University, Canberra
ABSTRACT- We determined whether populations of 118 bird species increased or decreased over 25 years in response to intensity of land use (pastoralism) and natural environmental variation. Our study area was the arid and semi-arid zone, encompassing 70 percent of the Australian continent. We used data collected by volunteer observers in two periods (1977-1981 and 1996-2001) for the Australian Bird Atlas, comprising 9200 bird surveys after extracting matching surveys conducted in each time period at the same location. For grid squares of one degree latitude and longitude we estimated the density of artificial water points (a surrogate for the intensity of grazing by cattle and sheep), change in rainfall, and change in vegetation condition (from time series of NDVI). We modeled the change in the probability of sighting a species within one degree squares between the two time periods, in response to these variables. We used a general linear mixed model accounting for components of variance within and between grid squares, spatial autocorrelation of grid squares, and dependence of variance on survey effort, and adjusting for systematic differences in survey effort between times and locations. We detected a range of responses to landscape characteristics at several spatial scales. For example, population change for one third of species was related to intensity of land use. We also detected overall trends in population status at bioregional- and continental- scales.
KEY WORDS: rangelands, monitoring, statistics, birds