Brolga Abstracts

Brolgas are threatened in southern Australia, and these studies look at habitats they need in the breeding and flocking (non-breeding) seasons, and conservation. The first abstract (summary) is from Rebecca Sheldon's thesis on Brolga flocking wetlands in SW Victoria. Then, two 2001 abstracts on Brolga breeding habitat.

Also in Ozcranes Research: Kristie King's 2008 abstract and full thesis on flocking Brolgas.


Rebecca Ann Sheldon: University of Ballarat, Victoria, Australia

Title The characterisation and modelling of Brolga Grus rubicunda flocking habitat in south-western Victoria: Relationships between habitat characteristics, Brolga abundance and flocking duration

Abstract Brolga Grus rubicunda use two distinct wetland habitats throughout their annual cycle, flocking and breeding habitat. Brolga flock for up to eight months of the year. Previous habitat characterisation studies have focused almost exclusively on breeding habitat. Until recently, systematic assessment of flocking habitat was scant.

Major aims of this study were to identify, characterise and model Brolga flocking habitat across south-western Victoria. The south-west Victorian Brolga population is allegedly discrete and uncertainty surrounds its current demographics. Habitat characteristic data obtained from field measurements and Geographic Information Systems (GIS) were combined to achieve these aims.

Flocking sites were identified through the compilation of existing records into a comprehensive database. Mapping of these sites enabled data to be obtained for relevant spatial and temporal variables. Twenty-nine wetland flocking sites were selected across south-west Victoria for analysis based on site fidelity, Brolga abundance and flocking duration. Data for 18 explanatory variables were statistically analysed to characterise flocking habitat. Important variables were identified though significant relationships with Brolga abundance and/or flocking duration. Three of these important variables were selected for model development. Potentially suitable flocking habitat was mapped across the study area and an accuracy assessment was performed.

Wetlands used by flocking Brolga consisted of deep freshwater marsh or permanent open water (fresh or saline). Wetland sites were generally greater than 30 hectares in area (82% of sites) and had low cover of emergent vegetation (80% of sites had <40% cover). Surrounding landuse within a 5 km buffer was predominately grazing (mean 65%) and cropping (mean 21%). Significant correlations were identified between wetland area and flocking duration (r = 0.44, p = 0.02), maximum water depth and flocking duration (r = 0.5, p = 0.01) and, the length of wetland perimeter within a 5 km buffer and maximum number of Brolga (r = 0.39, p = 0.04). The flocking habitat model identified 1,172 wetlands and a total wetland area of 37,522 ha. The model correctly identified 84% of study sites. Few modelled wetlands were sufficient in area to support large Brolga flocks.

Flocking habitat was highly variable and important factors in flocking site selection were not obvious. Habitat availability seems limited in the landscape. The conservation and creation of suitable habitat for Brolga flocks may be vital for the long-term viability of this vulnerable species in south-western Victoria.

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Claire Harding: University of Ballarat, Victoria, Australia

Title The use of remote sensing and geographic information systems to predict suitable breeding habitat for the Brolga Grus rubicunda in south-western Victoria.

Abstract The Brolga Grus rubicunda is listed as vulnerable in Victoria. The decline in the Brolga population of south-western Victoria has been attributed primarily to the drainage of breeding wetlands for agricultural purposes. The vast majority of known nest site locations are found on privately owned land and are highly susceptible to drainage and degradation. This research investigates the use of satellite imagery to identify the remaining potentially suitable nesting habitat for the Brolga in south-western Victoria.

Nesting habitat for the Brolga (shallow freshwater marshes and meadows) was identified using Landsat Thematic Mapper (TM) data for a region in southwestern Victoria. This was accomplished using the locations of known Brolga nest sites and applying a supervised classification procedure to locate spectrally similar landcover categories. Thematic maps were produced and nesting habitat acreages were computed, providing a regional assessment of existing and potential Brolga nesting sites. Accuracy assessment of the classified Landsat image revealed that 88% of predicted nesting habitat was correctly classified.

Proximity analysis on the distribution of nest sites was analysed to estimate breeding territory sizes. A minimum area of 452 hectares was observed for territorial nesting Brolgas in south-western Victoria. The absence of nesting pairs in the large number of wetlands classified as suitable nesting habitat may be accounted for by conditions and assumptions inherent in the data, unanswered questions concerning the behaviour of nesting Brolgas, the uncertainty that all nest sites in the study area were known, and the inability to detect certain pertinent landscape features and local variables.

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Matthew Herring, Nicholas Klomp and Ian Lunt: Charles Sturt University, New South Wales, Australia

Title The Brolga Grus rubicunda in southern New South Wales and northern Victoria: distribution, breeding habitat and potential role as an umbrella species.

Abstract An observer network of 220 people was established to determine current distribution and abundance, and locate breeding and flocking sites. Characteristics of breeding sites, other wetland sites used during the breeding season and non-Brolga control wetlands were compared to identify key habitat requirements.

Brolgas Grus rubicunda have declined severely throughout the study area, primarily from habitat loss and shooting. Less than 250 individuals remain, with major strongholds in the Urana, Corop, Dingee and Yarrawonga regions. Brolgas are primarily associated with landscapes where large wetland complexes remain, and are very rare in intensive irrigation areas.

Only 4.4% of Brolgas at five major flocking sites were immature, in contrast to over 15% in northern Australia. Less than 31% (10/33) of nesting attempts were known to be successful, with the first three weeks after hatching identified as the critical period. Most Brolga breeding sites were large (50 ha) remnant wetlands with extensive areas of water around 30 cm deep, and only the two largest sites supported more than one breeding pair. More than 90% of breeding sites were dominated by Eragrostis australasica or Eleocharis species, with emergent vegetation cover usually around 25% and 90 cm in height. In contrast, most other sites were small artificial watering points, lacking emergent vegetation and shallows, and supporting a greatly reduced avifauna. Brolga breeding sites supported significantly more bird species than control sites, especially threatened species.

The optimal breeding habitat characteristics for Brolgas corresponded with overall bird species richness and the habitat requirements of other threatened waterbirds like Australasian Bittern Botaurus poiciloptilus, which were recorded at 34% (11/32) of Brolga breeding sites. The Brolga is an effective communication tool for promoting wetland conservation. Conservation efforts targeted at Brolga wetlands will encapsulate the protection of many other species.

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More...

Read Matthew's magazine article on his project in Ozcranes Brolga section»


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