Abstract

In September 1996, ten captive yellow-footed rock-wallabies (YFRW) were reintroduced to Aroona Sanctuary in the Northern Flinders Ranges, South Australia. The reintroduction of the YFRW was to trial the effectiveness of captive propagation and release as a recovery tool for this species. This program, facilitated by the Royal Zoological Society of South Australia (RZSSA), illustrated the importance of cooperation, preparation, commitment of time and money, and veterinary involvement in a reintroduction program. Veterinary involvement included disease surveillance, selection of the fittest individuals for release, and acclimatization, monitoring, and pathology after release. Comparisons of microflora and parasite loads between captive and wild YFRW showed little variation. Consequently, no pharmacologic intervention was deemed necessary prior to reintroduction, apart from vitamin E/selenium supplementation. Short-term success can be credited, with an 80% survival rate and first-generation juveniles surviving past weaning.

Introduction

The YFRW exists in isolated colonies throughout its former range in South Australia (SA), New South Wales and Queensland. The SA subspecies, Petrogale xanthopus xanthopus, suffered a large decline since European settlement, due to habitat destruction, hunting, and the introduction of eutherian predators. Although hunting was outlawed in 1912, the pressures of carnivores, introduced competing herbivores, and pastoralism have created isolated pockets of animals with all its attendant problems. Although environmental management will be the key to the recovery of the YFRW, a trial reintroduction of captive-bred animals was sanctioned at a meeting convened for Petrogale spp. in 1994. Adelaide Zoological Gardens (AZG) has managed a captive colony of YFRW for 108 years. Capture of wild males and their incorporation into the studbook has seen this healthy captive population grow to 136 animals in eleven Australian institutions.² Seventy of these are kept in 6000 m², natural mallee paddocks at the Society’s open range zoo, Monarto Zoological Park (MZP). The zoo joined with the Department of Environment Heritage and Aboriginal Affairs (DEHAA) and Optima Energy (formerly the Electricity Trust of SA) to conduct the reintroduction trial. Support was sought and gained from the Zoological Boards of Victoria and New South Wales, the local community and surrounding pastoralists of Leigh Creek.

The site chosen for reintroduction was Aroona Sanctuary, the property of Optima Energy, and associated with the township of Leigh Creek. The sanctuary supported a YFRW colony, until they became locally extinct in 1982. The threatening processes at this site are not known but assumed to be a combination of high resident fox numbers, goat and sheep migration to the central Aroona Dam, and shooting. Apart from being within the historic range of YFRW, this site was chosen due to its association with Optima, its remoteness from wild YFRW colonies, and suitable habitat. Optima had initiated feral cat and herbivore control programs in association with revegetation at Aroona Dam. An intensive fox baiting and shooting program was added with further involvement from Optima and a commitment from RZSSA. The surrounding pastoralists embarked on a project of creating a 10-kilometre radius of 1080 baiting around the Sanctuary in January 1996. This “Buffer Zone” has proven very effective with spotlighting assessments showing a dramatic decrease of foxes in the area. (J. Crutchett, personal communication).

Disease Surveillance

Epidemics associated with high mortality rates in free-ranging macropods are rare in Australia. Diseases, such as toxoplasmosis, coccidiosis, necrobacillosis, and anemias caused by eperythrozoites and globocephaloides, have been isolated from macropod epidemics, however most of these disease outbreaks are associated with environmental stressors.⁵ Factors, such as drought, flood, nutrition, and overcrowding, have a large role to play in macropod dieoffs. Recently the epidemiology of macropod herpesviruses and epidemics in Macropus sp. caused by Wallal/Warrego viruses have been investigated as pathogens for this family of marsupials. Wallal virus was described in 1995 in response to an epidemic of blindness in wild kangaroos and euros across NSW, Victoria, and SA in 1993, 1994, and 1995.⁴ The Wallal and Warrego viruses are insect-borne, orbivirus-related organisms. Macropod herpesvirus (MHV) is widespread in Australian macropods and has caused fatalities in captive macropods, but no clinical cases have been reported in the wild.⁵ Once again clinical expression of this disease is likely to be a multifactorial problem resulting in immuno-suppression.

Serologic Testing

Serologic testing for MHV, Wallal virus, and toxoplasma resulted in no sero-conversion in 38 captive MZP YFRW (54 animals tested for Toxoplasma) or 3 wild YFRW from the Northern Flinders Ranges. From wild euros (Macropus robustus erubescens) inhabiting Aroona Sanctuary in 1996, there was 100% sero-conversion to MHV, 66% conversion to Wallal virus and no sero-conversion to toxoplasma. Four of five cats sampled from Aroona Sanctuary did show antibodies to Toxoplasma gondii.

Gastrointestinal Bacteriology and Parasitology

An extensive variety of organisms were isolated from feces (Table 1). Significant organisms in captive macropods could be Eimeria spp. and Salmonella typhimurium, however, they are not considered to be pathogenic in wild macropods, unless other factors causing microbiologic imbalance are experienced. Most were readily cultured from a high proportion of the captive and wild macropods with no clinical evidence of disease or poor condition.

Table 1. Selection of microorganisms and results of the survey

Skin Scraping

Skin scrapings and hair samples revealed Aspergillus versicolor and Heterodoxus ampullatus present at low levels in the captive population. Fungi have been isolated from hair samples from wild wallabies and the Heterodoxus louse is common in this species. There were no clinical signs or histories of disease associated with either of these ubiquitous organisms.

Selection of Individuals for Release

Wallabies were caught in large hanging nets set up in corral-style cul-de-sacs along fences. All animals between the ages of 2 and 5 years were anaesthetized with isoflurane via a face mask. Comparative weights, condition scores, pelage, and ectoparasite burdens were used as indicators of general health. Thorough clinical examinations were performed on each animal, paying particular attention to tooth/gum margins because of the common incidence of necrobacillosis (lumpy jaw) in captive macropods.

Over seventy complete blood profiles and biochemistries have been collated from 1995–1996 to create the “normal” blood profile for this species in captivity (values will be available in the next ISIS Reference Values, MedARKS). This profile helped to assess the health status of captive and wild YFRW. No inflammatory or organ problems were detected. Limited sampling (n=4) from wild macropods demonstrated a mean of 9.27 mg/L alpha-tocopherol. Sampling of captive YFRW (n=69) showed a mean of 2.06 mg/L. While this may not indicate a deficiency in these captive wallabies, selenium/vitamin E was injected intramuscularly at 0.02–0.025 ml/kg (Vitamin-E-Selen, 150 IU vitamin E and 0.5 mg selenium/ml).

Social and Environmental Acclimatization

The release group comprised two males and eight females. Six months prior to reintroduction, two groups of potential release animals, each with two males and seven females, were placed under minimal surveillance with no supplementary feeding and natural exposure to wedge-tailed eagles, a very common predator at Aroona Sanctuary. Species of browse and grasses similar to those at Aroona Dam could be found in their enclosures. Fecal analysis of scats from wild wallabies, euros, and the captive group were conducted to determine food preferences. It took a few months after release for the captive adults to change their food preference to predominantly browse, similar to YFRW in the wild.³ After a second veterinary examination, radio-collars were fitted to ten wallabies to test individual responses. The collars had been tried for 6 months on female wallabies at AZG, without event. One female panicked in response to the collar, which was immediately removed, and the wallaby was replaced with another female. One month prior to release, in-pouch joeys were removed from these females for hand-rearing. This procedure would avoid peak lactation at the time of release, and synchronize a birth at the point of release, thereby minimizing the time before the first generation of wild YFRW emerged from the pouch.

Monitoring and Deaths

Monitoring of the wallabies after release was accomplished by radiotelemetry. Radio-collars of individual frequency were fitted with mortality switches. A remote system of triangulation for locating each wallaby was used at least twice a day. Tracking teams provided continual assessment for the first 40 days, then once per month for the next 8 months and once every 3 months thereafter. This remote tracking system ensured minimal human interference to the wallabies after release, allowing rapid establishment of home territories. The wallabies have never ventured further than 1 km from the release site. Females have formed small home ranges with the male’s territory overlapping most of these.

Two wallabies have died since release. The first death was that of a male, 1 month after release. Post-mortem examination identified accelerated autolysis in the thoracic cavity, but no diagnosis. The second wallaby, a female, died 6 months after release. Post-mortem revealed severe purulent pleuro-pneumonia. Actinobacillus sp. has been cultured. No evidence of physical stress or injury was found to explain the origin of this pneumonia. The female had a 140-day-old healthy, female joey in the pouch. There was no indication of predation, starvation or parasitic diarrhea in either autopsy. A trapping program in April 1998 allowed six of the eight remaining radio-collars to be replaced and samples to be taken for future veterinary and biologic research.

Discussion

Veterinary investigation prior to release showed a high degree of correlation between organisms inhabiting the captive and wild YFRW. It was decided not to try to eradicate any of the organisms in the captive stock because of unknown consequences to the immunity and microbiologic balance. Vaccination against Wallal virus, MHV and Toxoplasma gondii is not possible and the risk of cross infection from the wild euros and feral cats at Aroona Sanctuary remains. A case of poxvirus causing clinical dermatitis was confirmed in a euro at Aroona and this disease may also be able to infect the released YFRW. Collection of blood after a period of pursuit and handling did not appear to produce a stress leukogram in the majority of YFRW, as indicated by the high lymphocyte/neutrophil ratio. Individuals occasionally show marked elevations in creatinine phosphokinase, but no overt cases of myopathy resulted. As the majority of animals examined at MZP satisfied selection criteria, reproductive histories formed the basis for final selection.

Conclusion

The success and motivation toward local conservation inspired by this reintroduction, are the result of a well-planned release protocol and several years of communication, dedication and commitment by the RZSSA. The positive results of this project extend beyond the survivability of the YFRW. In 1997, a large Land Care grant was awarded for expanding and improving the feral animal eradication program into the whole of the Aroona catchment basin. The local area school has received a grant to establish an automated tracking system. Optima Energy has funded a biologic survey of the region and the release group and their progeny also have the potential to provide ecotourism and research.

Australian animals and their organisms are unique, and epidemiology of their diseases is poorly understood. Veterinary involvement in reintroductions in Australia is important in assessing risk. The surveillance of disease, selection of individuals for release, adequate acclimatization and monitoring ensures maximum survivability of release animals and minimal impact on endemic populations. This is critical when dealing with the remaining fragmented populations of our many threatened species and to date the success of mainland Australian reintroductions has been poor.¹

Acknowledgments

The author acknowledges the “team” for funding and faith! The RZSSA, especially Ed McAlister, Suzy Barlow, and John Crutchett; Optima Energy, especially Beat Odermatt; DEHAA; Zoo Boards of Victoria and NSW; Leigh Creek Area School, especially Colin Murdoch, the pastoralists, Allan Salisbury (Transceiver Services, SA), and Steve Lapidge. Vetlab, South Australia, the Australian Animal Health Laboratory, Victoria and the Queensland Agricultural Biotechnology Centre performed the clinical pathology and serology.

Literature Cited

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