Assessment of Seasonal Habitat Characteristics as Predictors of Habitat Suitability for the Threatened Ornamental Snake (Interim Report)

The ACARP funded ornamental snake Research Program is being undertaken to provide a greater understanding of the habitat usage and ecological requirements of the threatened ornamental snake (Denisonia maculata) within the Bowen Basin mining province.  The ornamental snake is recognised as "signature species" of the Brigalow Belt Bioregion and is listed as vulnerable under the provisions of the Nature Conservation Act 1992 (NC Act) and Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act).  

 

The primary aim of the research program is to:

• Collect quantitative data to support the hypothesis that brigalow-gilgai formations support a unique suite of characteristics and microhabitats required to support the ornamental snake as opposed to adjacent habitats within the distribution range of the species; and
• Utilise the improved understanding of this species' habitat and ecological requirements to improve conservation outcomes and long-term management practices within the Bowen Basin mining province and the known distribution range for the species.

 

The benefits of the proposed research are anticipated to:

• Support a more informed approach by the mining industry in compliance with legislative requirements and responsibilities;
• Improve conservation outcomes and long-term management practices on mine-affected lands within the Bowen Basin mining province; and
• Enhance management decisions in regard to impact assessment of mining proposals, the allocation of non-mined lands as part of end of mine land use plans and the provision of suitable off-site lands as part of a "green offsets" strategy.

 

Detailed field investigations examining soil, vegetation and fauna habitat variables were undertaken.  Survey sites were selected on the basis that they are known to or are considered likely to support ornamental snake populations.  Seven brigalow-gilgai locations (mound and depression profiles) and six representative eucalypt habitat sites (where the presence of snake populations had not been previously recorded despite extensive survey effort under suitable conditions) were selected.  

 

Fauna habitat characteristics that are known to influence the distribution of a range of fauna species within habitat areas are analysed to determine the influence of these characteristics on the presence or absence of the ornamental snake within the representative survey sites chosen, namely brigalow-gilgai habitats and adjacent eucalypt communities, and the habitats that are supported within these survey sites.

 

Analysis of the data collected from each of the brigalow-gilgai survey sites revealed great differences in the characteristics of each site.  The presence and association of brigalow on these soils is primarily due to the ability of brigalow to withstand the stress of having its roots sheared due to the constant shrinking and swelling movements of the clay soils to form gilgai (pers. comm. J. Burgess 2008).  There appears to be no correlation between the sites in terms of similar habitat characteristics other than each site supports gilgai formations on deep cracking clay soils.

This in itself is a significant observation as it provides quantifiable evidence to support the hypothesis that ornamental snakes require the characteristics supported in the gilgai habitats, namely periodic ponding of water followed by formation of deep soil cracks for refuge, which are not present nor supported within habitats found adjacent and locally to the brigalow-gilgai associations.  

 

The formation of ponds which persist for extended periods, up to several weeks, provides critical breeding habitat for frogs, which are thought to be the primary diet of the ornamental snake.  Absence of this habitat resource outside of the brigalow-gilgai formations would appear to restrict the distribution of ornamental snakes to within the boundaries of this habitat during the wet season.

 

The development of deep ground cracks during dry seasonal conditions is thought to be a primary refuge source for ornamental snakes.  The results collected from the eucalypt habitats showed that there was an absence of deep soil cracks.  The absence of these refugia is a significant finding from this study.

 

The variety of fauna habitat characteristics that were measured and assessed for this study, namely presence/absence of ground cracks, fallen timber, leaf litter cover etc., form the basis of any habitat characterisation for an ecological assessment of vertebrate fauna supported within an area.  

 

The apparent lack of ground timber to provide suitable dry season refuge in the eucalypt communities is of interest.  This is likely to be the only form of possible refuge for snakes during dry times and, if in low abundance, provides limited habitat.

 

In eucalypt habitats (other than those surveyed) where ground timber has been in low to common abundance, it could reasonably be expected that, with enough survey effort targeting these habitats, snakes would have been found hibernating under such timbers during the dry seasons.  The authors' 10 years of experience conducting detailed fauna surveys within such habitats within the Bowen Basin, where resources such as natural and windrowed timber were common, has failed to observe any ornamental snakes seeking refuge in these habitats.  It is of interest that, from these resources, a range of other faunal groups have been observed, for example, pythons, elapid snakes, geckos, skinks, goannas, dragons, frogs and small ground mammals.

 

The capacity of the soils identified within the brigalow-gilgai survey sites to form deep cracks and, following rainfall, form ponded areas appears to be the main criteria for the distribution and selection of habitats by the ornamental snake.

 

Radio Tracking

The tracking study has provided evidence that, based on the data collected from two specimens, ornamental snakes:

• Are restricted to the brigalow gilgai habitat associations and do not move in/out of adjacent habitat types when the gilgai are dry/flooded;
• Move short distances within this habitat type during both late summer and over winter which indicates that these animals do not undergo full aestivation through winter months, but do undertake sporadic movements within the habitat type;
• Reside in the wide and deep soil cracks within suitable habitat at relatively shallow soil depths;
• Apparently absorb and retain heat from the soil; and
• Are susceptible to the impacts of cattle grazing during periods when gilgai support water, the soil is saturated and cattle access can significantly alter the structure and integrity of gilgai form and function.

 

This tracking study has provided preliminary data on the biology, ecology and habitat usage of the ornamental snake. This component of the study has been extended further and additional ornamental snakes have been implanted with radio transmitter are currently be monitored.

 

Management Implications

Results from the study overall indicated the following:

• Habitat management for ornamental snakes should be focussed on brigalow/gilgai formations, regardless of the presence/absence of actual brigalow shrubs/trees;
• The ornamental snake may potentially be susceptible to the impacts of direct cattle access to gilgais during wet periods. Cattle grazing management plans need to be established for areas suspected of supporting ornamental snakes;
• As snakes appear to reside at shallow depths within the soil profile and the nature of the soils are such that it requires mechanical shrinking and swelling processes to form the cracks within which the snakes reside, any process which disturbs the land form, i.e. clearing, ploughing, erosion, development of access tracks/drill lines etc has the potential to significantly impact the ornamental snake.

 

Management recommendations will be reviewed following the completion of the additional tracking study.