Cane toads

Wildlife at threat from cane toads: Identification of susceptible frog, snake and small mammal taxa and possible conservation actions

David Pearson

Science Division, Dept of Conservation and Land Management

PO Box 51 Wanneroo WA 6946

Email: davidp@calm.wa.gov.au Ph: (08) 9405 5112

Abstract

 Cane toads have clearly impacted on some species, such as the northern quoll, leading to severe population declines in Queensland and the Northern Territory (NT). However, our knowledge of the effects of cane toads on most taxa is poor due to:

• the lack of targeted studies;
• complications with other factors such as fire and seasonal differences in rainfall;
• the use of inappropriate sampling strategies; and
• limited pre-toad data.

To plan adequate and effective conservation actions to prevent extinctions or precipitous population declines, we need to identify those species at risk, as well as those that can tolerate the presence of cane toads.

This study will complement and build on research being conducted in the NT and proposed in WA, focusing on frog, reptile and small mammal species that have not been examined for their response to cane toads; especially those with restricted distributions around the East Kimberley region. A variety of techniques will be employed including frequent frog and tadpole assemblage surveys (calls and population counts) in a range of wetlands (assistance provided to Dale Roberts, University of Western Australia (UWA) and Paul Doughty, Western Australian Museum (WAM), the collection of road-kill frogs and snakes to determine diets, and radio-telemetry of pythons and known frog-eating snakes with the assistance of volunteers and the local community.

Also proposed is a collaborative study with Ben Phillips and Rick Shine ( University of Sydney ) on modelling the spread of cane toads by updating an existing database with recent NT information and some direct dietary preference trials with small mammals at the Fogg Dam (NT) study site and at Kununurra. Finally, the study will assess possible management actions to prevent the invasion of particular habitats (such as islands, or high value conservation sites) and to reduce the impact of cane toads in the landscape. This will be achieved by working with other researchers, and trialling traps and other techniques as they become available.

Introduction

The advance of cane toads towards Western Australia has caused tremendous concern about their impacts on the native fauna of the Kimberley region. While the effect of cane toads on Northern Quolls (Dasyurus hallucatus, Oakwood 2003), some goannas (Burnett 1997) and a couple of snakes ( Phillips , Brown and Shine 2003) has now been documented, data on impacts on other vertebrates is either anecdotal or non-existent (for further references see the recent listing of cane toads as a Key Threatening Process under the EPBC Act, www.deh.gov.au/biodiversity/threatened).

This discussion paper presented at the Kununurra Cane Toad Forum sought to outline some of the proposed research to identify taxa of terrestrial vertebrates that were at significant potential risk from cane toads, should their advance continue. The research comprises a number of targeted collaborative projects with researchers from the University of Sydney (Professor R ick Shine and Ben Phillips ), the University of Western Australia (UWA) (Professor Dale R oberts ), the Western Australian Museum (WAM) (Dr. Paul Doughty ) and the Australian R eptile Park (Mr. John Weigel ). In addition, the research aims to directly involve local communities, organizations (such as Save Endangered East Kimberley Species (SEEKS)) and government agencies in the East Kimberley . This has the benefit of allowing the public to observe and understand the impacts of cane toads first-hand, as well as permitting research on some of those species (especially large predators such as pythons) that are often difficult to locate or occur at low densities.

The Kimberley region contains many endemic vertebrates as well as species with broader tropical distributions that are likely to be severely affected by cane toads. However, much of the information available on cane toad impacts is anecdotal or based on studies that have lacked sufficient pre-toad data to determine the impact of cane toads relative to other environmental variables such as rainfall or disturbances such as fire. Further, many species have not been studied at all and we can only guess the probable effect of cane toads.

Given the proximity of cane toads to the East Kimberley , it is important to establish monitoring and research projects now, in advance of the potential arrival of cane toads to ensure that adequate data on existing assemblages of terrestrial vertebrates are collected so impacts can be detected.

Is this approach fatalistic? Should we be putting all our efforts into stopping the cane toads and not worrying about research on impacts? I argue that if cane toads cannot be stopped despite our best efforts, and we have not conducted adequate research work, we will have lost an opportunity to understand their impacts on East Kimberley and other northern fauna. This would severely limit our capacity to understand the susceptible elements of the fauna and so implement management efforts to prevent extinctions. There are actions that can be taken to preserve vulnerable species should cane toads over-run the Kimberley . Many options have not yet been explored and some are outlined at the end of this paper.

Northern Territory experience

In December 2004, I travelled to Darwin and Kakadu National Park (Kakadu) to speak to researchers, managers and other observers to assess how the threat of cane toads had been handled. In particular, I wished to identify those species that are likely to be threatened by the toad in W.A. based on the Top End experience and any specific measures that were being employed to restrict the toad’s spread or impact. There were over 30 projects concerning cane toad impacts that have been completed or were underway in the N.T. I was unable to visit all these researchers due to the short duration of my trip.

Dr Tony Griffiths (Key Centre of Tropical Ecology, Charles Darwin University ) has been studying a variety of goanna species using radio-telemetry, including Varanus panoptes, V. gouldii, V. indicus in Kakadu and closer to Darwin . R esults indicate the collapse of V. panoptes populations upon the arrival of cane toads. Longer term impacts are unknown. Problems with transmitter reliability and the later-than-expected arrival of cane toads have restricted the collection of robust data on other species.

Professor R ick Shine ( University of Sydney ) received an A R C grant to examine cane toad impacts at Fogg Dam, the site of a long-term snake ecology project. Over the last 10 years R ick and co-workers, Dr Greg Brown, Dr Thomas Madsen, Ben Phillips and many volunteers have measured and individually marked over 8,000 water pythons, Liasis fuscus (this work is now being continued by Dr Thomas Madsen, University of Wollongong), 4,000 Keelbacks (Tropidonophis mairii), 2,000 Slaty-grey Snakes (Stegonotus cucullatus) and 1,000 Macleay Water-Snakes (Enhydris polylepis). In addition, this group was catching a sample group of each of the latter three species and as well Death Adders (Acanthophis praelongus) to implant transmitters (50 of each), to be released when cane toads arrived at Fogg Dam to examine immediate impacts. Since cane toads were only 30 km from their study site and expected to arrive that wet season, they had a rare opportunity to study the direct impacts of cane toads with the benefit of long-term pre-toad data. An Honours student, Matt Greenlees was carrying out field laboratory trials on the feeding preferences of several species on snakes in relation to cane toad adults and metamorphs, including an examination of inheritance of avoidance or resistance to bufotoxin. A large array of pens had been constructed on the floodplain at Beatrice Hill to examine toad impacts on invertebrate abundance and on shelter use by native frogs and reptiles.

A long-term employee and resident of Kakadu, Mr. Greg R yan (Operations Manager) followed the movement of cane toads into Kakadu in 2001. He recounted how the toads reached Kakadu across seemingly inhospitable sandstone escarpment to the east of the Park by following small creeks and drainages in the Wet season.

Another long-term resident of the area, Mr. Dave Lindner (former ranger, now running a buffalo farm for the Gagadju Association and a keen naturalist) currently lives at Nourlangie. He had provided logistic support to an American researcher, Dan Holland who conducted intensive radio-telemetry of goannas especially Varanus panoptes during the invasion of cane toads. Dave Lindner noted that mature V. panoptes had disappeared around the Nourlangie area and he now only saw small individuals (presumably sub-adults). A family of Northern Quolls that lived in his sheds had all disappeared, as had Olive Pythons, which were frequently observed prior to the arrival of cane toads. He had only seen the occasional olive python in woodlands on ridge lines.

Dr. John Woinarski (Ecologist- NT Department of Infrastructure, Planning and Environment, DIPE) with co-worker Michelle Watson (PhD student) compared vertebrate faunas on sites throughout Kakadu before and after cane toad invasion. Since the survey techniques used were not designed to specifically sample the most likely affected species (frogs and predators of frogs), the generalized results were that goannas considered as a group had declined, as had Gilbert’s Dragon (Lophognathus gilberti). The low capture rates of dasyruids prevented any analysis of the impact of cane toads on this potentially susceptible group. The ability of toads to raft well offshore was noted by Dr. Woinarski. Individual cane toads had rafted/swum 20 km out to the St Edward Pellew group of islands.

In recognition of the tenuous position of Northern Quolls , DIPE has translocated Northern Quolls to Astell and Pobassoo Islands under the Island Arc Program (managed by R ob Taylor). Monitoring of the quolls was done in collaboration with Aboriginal communities. In addition, R ob Taylor was organizing the “Great Toad Trap” competition in Darwin . Finally, I spoke to Bill Freeland (GHD Consultants). He was a former Parks and Wildlife Commission manager and researcher. He had recently undertaken a review of the environmental impacts of cane toads in relation to the expansion of the Ord irrigation scheme. He pointed to the lack of rigorous data on the impacts of cane toads on biodiversity.

The visit to the Northern Territory identified a number of points that influenced the projects that were subsequently developed and are presented here:

1. Despite the amount of effort devoted to researching the impact of cane toads, there are few examples of unequivocal data to illustrate their effects on biodiversity. Studies have been beset with problems including: lack of pre-toad data, low sampling intensity, poor prediction of toad arrival, technical problems (transmitters, etc.), other complicating environmental factors (low rainfall, fire) and difficulty in assigning cause of death of study animals.

1. The Northern Quoll is the only mammal that has been demonstrated to show a clear response to cane toads. They attempt to eat toads, die and local populations go extinct. Northern Quolls appear to survive only in rocky areas where toad numbers are presumably lower. The response of other mammals is unknown, especially dasyurids (marsupial carnivores and insectivores) that are potential predators of cane toads.

1. Frog assemblages are affected but interpretation of “toadpole” data ( University of Queensland ) has been limited by an observed decline in frogs prior to the arrival of cane toads (probably due to low rainfall) and technical difficulties.

1. Populations of Varanus panoptes are clearly affected at least in the short term; there may be a later recovery but this has not been adequately researched (Freeland, pers. comm.). Insufficient data have been collected on other goannas to establish any clear trends. Smaller lizards have not been studied, although Watson and Woinarski (2003) noted that Gilbert’s Dragon had declined.

1. There are no current studies on the impact of cane toads on invertebrate communities (especially land snails of which there are many Kimberley endemic species), terrestrial small reptiles (skinks and geckoes- there is one early paper from Papua New Guinea , Schulz-Westrum 1970, that suggests an impact), turtles and freshwater crocodiles and frog assemblages in the East Kimberley .

1. Island faunas are at risk. Toads have rafted at least 20 km to colonise islands along the NT coast.

Proposed projects to examine the impact of cane toads on vertebrate biodiversity

As a consequence of reviewing the available literature and talking to colleagues in the Northern Territory and Western Australia , the research projects outlined here are designed to fill gaps in the existing research effort. I maintain the view that it is best to involve relevant agencies, institutions and individuals to ensure that the work is both cost effective and carried out by experts in the relative subject areas. Broad-scale monitoring using standard survey techniques is unlikely to enable testing of cane toad impacts as typically insufficient data are collected on those species (such as large mammalian and reptilian predators) most likely to be impacted. Woinarski et al. (2004) noted in a recent paper on Litchfield National Park fauna (NT) that: “The apparent instability of fauna species and communities in this system provides a considerable challenge for broad-brush (that is vertebrate community-wide) monitoring. Power analysis demonstrated that, for most species, more than 1000 sample sites are needed to be 90% certain of detecting a 20% change in abundance.”

Rather than trying to monitor the impacts of cane toads on a vast array of vertebrate fauna, it makes sense to concentrate on those taxa not being studied elsewhere and those that are most threatened and most likely to be impacted.

Targeted research on threatened, endemic and highly susceptible taxa is more likely to provide useful data upon which management decisions can be made. Nonetheless, there is also a need for survey work, especially on poorly known groups such as frogs and on Kimberley islands so that well-informed decisions can be made to conserve the Kimberley fauna.

 Project 1: Predictive modeling of cane toad spread and final distribution

 One of the problems facing managers and researchers is understanding when cane toads will arrive in particular places, because spread rates vary with a range of environmental factors. Ben Phillips ( University of Sydney ) developed a large database on the spread of cane toads across Queensland and used climatic layers in a GIS application to model the spread. This project would update the database with NT data, incorporate landform, drainage and soils information for the Kimberley and provide a model for the spread of cane toads and the likely routes of invasion. This project would require some GIS assistance from CALM staff.

Proponents: University of Sydney ( R ick Shine / Ben Phillips ) and CALM (D. Pearson)

Project 2: Determining the potential impacts of cane toads on small mammals and reptiles

Very little is known about the impact on small terrestrial mammals (except quolls) and most reptiles. This study proposes the employment of a post-doc. on an A R C-linkage grant over 3-5 years and based in Kununurra, but also working at Fogg Dam in the N.T. Feeding preference trials on a variety of dasyurids and predation/ feeding preference trials on some reptiles (large/ small skinks and geckoes) that occur in the NT and Kimberley would be conducted using existing facilities at Fogg Dam. Basic information as to whether or not, various taxa will actually consume different sized cane toads will provide the first information on the probable direct impact of toads. This in turn, will guide the establishment of focused research on particular vulnerable taxa. Pens would also be established in Kununurra to undertake complementary research on East Kimberley endemics and to examine inheritance of resistance to bufotoxin.

Proponents: University of Sydney ( R ick Shine ) and CALM (D. Pearson)

Project 3: Impact of cane toads on frog-eating snakes

Several species of snakes have been found to die when they attempt to eat cane toads and can cause population declines. This study would research the direct impact of cane toads on a variety of snake taxa in the East Kimberley concentrating on those not yet studied- especially the Olive Python, Black-headed Python, R ough-scaled Python and the Ord Snake (Suta ordensis) Telemetry and road observation transects would be used and this project would rely on strong community involvement to undertake regular radio-telemetry and to directly observe cane toad impacts during their invasion.

Proponent: CALM (D. Pearson) with community participation

Project 4: Alcoa frog watch research project: pre-cane toad Kimberley frog communities

Team: Paul Doughty (WAM) & Dale R oberts (UWA), in collaboration with David Pearson & Norm McKenzie (CALM)

This project is currently underway. The probable arrival of the cane toad in the Kimberley region is likely to change the native frog communities forever. However, there are several years, before the cane toad is predicted to arrive, to study the structure of native frog communities and to establish quantitative estimates of composition and abundance to document cane toad impacts.

Quantitative surveys of breeding ponds for calling males and tadpoles are proposed. Two main study areas will be established along sealed roads near Kununurra-Wyndham and Broome-Derby. We are also looking to establish interior and coastal sites (e.g. Mornington Station, Mitchell Plateau) to provide a better picture of the region, but logistics of working in these areas will be more difficult in the wet season owing to the closure of roads. Expeditions to remote regions will also be undertaken to better understand current distributions and to discover new species (especially in the genus Uperoleia).

Alcoa Frog Watch has provided funding for 3 years which will cover field expenses for several trips a year to work the sealed roads in the east and west Kimberley, carry out tadpole rearing, support student projects plus a few collecting expeditions to more remote regions.

Our research is primarily aimed at understanding the basic biology of Kimberley frogs; community structure, breeding biology and larval ecology. Our surveys will be designed to provide rigorous quantitative estimates of species across different habitat types. Our data will therefore be useful for determining the impacts of cane toads during and after the initial invasion. Evidence of cane toads severely affecting specific species in the eastern Kimberley could lead to preventative management strategies in the western and interior Kimberley .

Outcomes of our research are:

• a quantitative baseline of species composition and abundance across a range of habitats in three main areas (east, west, interior);

1. an understanding of male calls – production of Kimberley frog calls CD;
2. documentation of larval stages – production of field guide to tadpoles;
3. a better understanding of species ranges; and
4. discovery of new species.

Possible management solutions

A number of options have been advanced to mitigate the likely impact of cane toads on the native fauna. Some of these have already been attempted in the NT, while others are under consideration. R esearch is needed to resolve which options will be useful in the armoury against toads. Some options include:

1. Stopping the advance of toads using traps or barriers;
2. Preventing cane toads from reaching Kimberley islands (traps, regular monitoring);
3. R emoval of cane toads should they raft to islands (traps, attractants);
4. Translocation of susceptible/ threatened fauna to islands;
5. Fencing around restricted populations of susceptible fauna (e.g. land snails);
6. Captive breeding and release after the initial cane toad front;
7. Selection for individuals with behavioural or physiological resistance to cane toads; and
8. Biological control of cane toads (CSI R O are working on this aspect).

Conclusion

Cane toads have the potential to greatly alter the vertebrate assemblages of the Kimberley region, but we lack understanding of what those impacts may be or how their effects can be reduced through management action. Collaborative targeted research on impacts and potential solutions offers the best hope to fill knowledge gaps.

References

Burnett, S. 1997. Colonising cane toads cause population declines in native predators: R eliable anecdotal information and management implications. Pacific Conservation Biology3:65 - 72.

Oakwood, M. 2003. The effect of cane toads on a marsupial carnivore, the northern quoll, Dasyurus hallucatus. Unpublished progress report to Parks Australia North. February 2003

Phillips, B. L., G. P. Brown & R . Shine. 2003. Assessing the potential impact of cane toads Bufo marinus on Australian snakes. Conservation Biology17:1738-1747.

Schultz-Westrum, T.G. 1970. Conservation in Papua and New Guinea . Final report on the 1970 World Wildlife Fund Mission.

Watson, M, & Woinarski, J. 2003. A preliminary assessment of impacts of cane toads on terrestrial vertebrate fauna in Kakadu National Park . Unpublished report to Kakadu R esearch Advisory Committee, February 2003

Woinarski, J.C.Z., Armstrong, M., Price, O., McCartney, J., Griffiths , A.D. and Fisher, A. (2004). The terrestrial vertebrate fauna of Litchfield National Park , Northern Territory : monitoring over a 6-year period and response to fire history. Wildlife R esearch 31 : 587-596.