Introduction
Extinction rates for vertebrate species are higher in southern Australia than almost anywhere else in the world, and saving endangered taxa is crucial for conserving biodiversity. To do this effectively, researchers need to understand the processes that threaten wild populations, and to develop novel solutions to those problems in close collaboration with wildlife management authorities and other stakeholders. This projects initiates such an understanding and collaboration, and focuses on saving the endangered broad-headed snake (Hoplocephalus bungaroides) from extinction. Over the next four years, researchers from the University of Sydney, Forests NSW, Zoos Victoria, and the Australian Reptile Park, will carry out ambitious landscape-scale field experiments to simultaneously test hypotheses about threatening processes, and to restore habitat quality to reverse population declines.
Background
Human-wrought changes to natural habitats are regarded as the single most important threat to biodiversity worldwide. Hence, we urgently need to understand what processes lead to endangerment, and develop appropriate ways to restore habitats for endangered species. This project will address these broad aims, and will focus on bringing about recovery of a critically endangered vertebrate, the broad-headed snake, Hoplocephalus bungaroides.
The broad-headed snake is a colourful, medium-sized (to 90 cm total length) nocturnal, front-fanged venomous snake that is entirely restricted to sandstone rock outcrops in near-coastal areas of south-eastern New South Wales. The species’ historical geographic range extended from Ulladulla in the south, Bathurst to the west, Mudgee to the northwest, and Gosford to the northeast. This region is one of the most highly urbanised in Australia, and broad-headed snakes have experienced severe population declines over the last 200 years. In the first authoritative book on Australian snakes published in 1869, Gerard Krefft noted that these spectacular snakes were once common along the shores of Middle Harbour, but were becoming scarce due to the removal of exfoliated sandstone rocks and boulders for landscaping suburban gardens. That process has continued unabated to the present day, with broad-headed snakes now either rare or absent from the majority of sites in which they are known to have occurred. Fortunately, broad-headed snakes still occur in Morton National Park, where Jonathan Webb and Rick Shine have conducted ecological research on these animals for the last 16 years.
As a result of this long-term research, we now know a lot about the ecology of the broad-headed snake. During the cooler months of the year, broad-headed snakes thermoregulate underneath ‘hot rocks’ created by thin sun-exposed sandstone exfoliations. Individual snakes often wait in ambush under their sun-warmed rocks – sometimes for weeks at a time – to capture unwary lizards that enter the crevices. In summer, when thin surface rocks become too hot for snakes to tolerate, adult males and females disperse to forests, where they shelter in tree hollows. In autumn, when rock temperatures are cooler, the snakes return to the rock outcrops, and both sexes show a high degree of philopatry, and often re-use the same rocks each year. The broad-headed snake has a ‘slow’ life history, with females reproducing infrequently (once every three years), and young snakes growing slowly and maturing at ages of 5 or 6 years old. This slow life history, coupled with the snake’s reliance on sun-warmed rocks for shelter sites, make it extremely vulnerable to habitat disturbance, particularly bush-rock removal. Indeed, recent survey work has shown that the species is locally extinct in areas where bush-rock has been removed.
Intriguingly, broad-headed snakes are also threatened by a more insidious form of habitat change – the overgrowth of rock outcrops by encroaching vegetation. Over the past 200 years, Europeans have suppressed wildfires, and consequently, vegetation structure has changed in some areas. Recent analysis of a time series of aerial photographs of sandstone plateaus near Nowra revealed that vegetation cover has increased on several plateaus where broad-headed snakes are rare. Presumably, these changes may have been caused by altered fire regimes, and perhaps, by the loss of browsing rock wallabies which have disappeared from many sandstone plateaus in south-eastern Australia. Irrespective of what caused this increase in vegetation density above rock outcrops, the challenge we now face is how best to reverse this process to create a mosaic that includes open areas.
Habitat degradation, via the removal of rock by rock thieves, and by shading of remaining rocks due to vegetation overgrowth, appears to be the main factor responsible for the endangerment of the broad-headed snake. This project seeks to bring about recovery of the broad-headed snake, by developing ways to: (1) restore degraded rock outcrops where bush-rocks have been removed, and; (2) manipulating heavily shaded habitats to bring about an increase in sun-exposed rocks. Although habitat restoration appears straightforward, we need to develop new methods if our restoration work is to be successful. For example, we could add quarried sandstone rocks to areas where bush-rock has been stolen, but these rocks are widely used by landscape gardeners, and are likely to be stolen by rock thieves. An inexpensive, long-lasting, functional and aesthetically acceptable solution to this dilemma is to use fibre-crete rocks created from silicon moulds of natural rocks.
Scientific Objectives
This project will carry out landscape scale experiments to examine whether it is feasible to restore habitats for the endangered broad-headed snake. We will also carry out survey work, both to establish the current geographic distribution of the species, and to develop predictive models which will allow us to test our hypotheses about the causes of endangerment of this species. Finally, genetic studies will allow us to determine whether broad-headed snake populations are genetically distinct from one another. This information will assist future captive breeding programmes that aim to bring about population recovery via release of captive-bred progeny.
This project aims to:
Outcomes
The research will provide a practical solution to a key threatening process - bush-rock removal - that poses a serious threat to Australian ecosystems. By developing novel ways to restore degraded rock outcrops, the research will not only benefit the endangered broad-headed snake, but also the diverse assemblage of invertebrate and vertebrate species that use sandstone rocks for shelter and nest sites. The research will contribute to conservation planning in a broader sense also, because it will develop novel collaborative science-based approaches to habitat restoration and species recovery. Importantly, the kinds of methods that we will develop will be ideally suited to implementation by local community groups to restore habitat in their local areas.
Researchers and Collaborators
The principal researchers working on this project are Professor Rick Shine, Dr Jonathan Webb, David Pike, and Ben Croak (University of Sydney), Dr Scott Keogh and Dr Joanna Sumner (Australian National University), Robert Pringle (Stanford University), and Trent Penman (Forests NSW).
Staff from the New South Wales Department of Environment and Conservation (DEC) are providing logistical support and assistance with field surveys.
The Australian Reptile Park (ARP) and Zoos Victoria (ZV) have developed captive breeding programs for broad-headed snakes (with a view to eventually providing offspring for repatriation to restored habitats), and maintain significant public education displays associated with captive specimens.
Forests NSW (FNSW) is responsible for sustainably harvesting timber resources in NSW forests, including areas containing broad-headed snakes, and they are helping to develop management plans for conserving broad-headed snake populations on the lands that they control.