Monitoring continental movement patterns of the Australian Bustard Ardeotis australis through community-based surveys and remote sensing

Abstract

Many birds of Australia's arid and monsoonal regions are characterized by dispersive or nomadic movements and large population fluctuations in response to variable climatic conditions. These characteristics, compounded by our generally limited knowledge of bird movements and population dynamics (in part due to limited research effort in these sparsely-populated rangelands), complicate population monitoring and conservation for such species. Here we employ mail surveys of landholders across continental Australia to assess the distribution and movement patterns of the Australian Bustard Ardeotis australis. We combine data from these simple mail surveys with more sophisticated techniques that allow for tracking the flux in rainfall patterns and vegetation greenness over broad spatial and temporal scales, to identify and describe the responses of bustards to seasonai and climatic variability. Our results demonstrate that residency patterns of bustards vary widely across Australia. The seasonality of bustard occurrence is generally more pronounced in regions characterized by predictable seasonal conditions. Seasonal patterns are also evident in more climatically unpredictable regions, although here they may be increasingly overlaid by more idiosyncratic movements as a result of longer term variation in rainfall and associated patterns of primary productivity. We found limited evidence that bustards respond to inter-regional irregularities in rainfall events, suggesting that nomadic movements are generally not continental, but rather intra-regional. However, longer term data sets that cover several more, or more extreme, climatic fluctuations than that considered here, are needed to assess these relationships adequately. To a lesser degree and differently between regions, respondents reported that bustards are also associated with fire, grasshopper outbreaks, crop agriculture and drought. They are most abundant across the savannahs of northern Australia extending to parts of the Pilbara and recently cleared regions of the Brigalow Belt in eastern Queensland. In southern Australia, bustards are perceived as shor-term, irregular visitors whereas more permanent populations persist in northern and northeastern regions. While there are inherent limitations to such data, the study illustrates the utility of incorporating rangeland users into the types of large-scale monitoring programmes required to assess the distribution and movement patterns of highly mobile birds or species characterized by large population fluctuations.