Assessing the impact of drought on the population dynamics of an endangered wallaby rescued from extinction by a flagship translocation program

A project undertaken at the School of Life Sciences, University of Queensland, and supervised by Anne Goldizen, Dominique Sigg, Anthony Pople and Andrew Lowe

BACKGROUND:

The bridled nailtail wallaby (Onychogalea fraenata) is one of the most endangered macropods in Australia and underwent a dramatic decline, from an extensive range throughout semi-arid eastern Australia to a single remnant population in central Queensland. The species was declared extinct by the 1930s but a small population was rediscovered in central Queensland in 1973 and later protected by the establishment of Taunton National Park. This last remaining wild population of bridled nailtail wallabies fell to fewer than 500 individuals in the mid-1990s during a protracted drought. A recovery plan was developed and a key goal of the plan was to establish translocated populations throughout the former range of the species. In 1996, a translocated population was established at Idalia National Park, QLD, on the western edge of the species' former range. This was a joint project between Queensland Parks and Wildlife (QPWS) and the University of Queensland (UQ), involving intensive monitoring of the translocation for the first 3 years.

A free-ranging population was successfully established at Idalia; released animals showed high survival and successfully reproduced, and the population increased in size and expanded in distribution from the time of the first release in 1996 to the end of the initial monitoring period in 1999. Regular monitoring continued until the end of 2000, by which time the population had expanded to over 800 individuals. A study of the genetic structure and diversity of both the wild and translocated populations during 1996-2000 is currently being completed by Dominique Sigg at the University of Queensland. This study has found a reduction in genetic diversity of the translocated population, which was established largely from animals that had been bred in captivity for many generations from a small founder stock. In addition to this, the translocated population at Idalia shows significant genetic differentiation from the wild source population.

Between 2001 and 2003 Queensland suffered a serious drought that resulted in a dramatic decline of the translocated population from over 800 to fewer than 200 animals. There is no information at this point on the extent to which the population is recovering from the drought as minimal monitoring has been carried out since 2000. Long-term monitoring and an assessment of the impact of a drought on the population have been identified as important ongoing goals for the management of this translocated population. Furthermore, as no new genetic stock has been added to the population since the first release of a small number of wild-caught animals, and the population has suffered a further decline due to drought, an assessment of the current genetic diversity of the population is required.

PROJECT AIMS:

The aim of this study is to assess the current population dynamics and genetic diversity of a translocated population of bridled nailtail wallabies after a severe drought, and to make recommendations to managers to ensure the continued success of the translocation project.

The specific project goals are to:

  1. Assess the population size, reproductive output and geographical distribution of the translocated population after a severe drought, and determine if the population is increasing and expanding again.
  2. Assess the genetic diversity of the translocated population and compare to analysis of genetic diversity already carried out both on the translocated population before the drought and on the wild population.
  3. Make recommendations for the ongoing management of current and future translocation projects, particularly in regard to maintaining levels of genetic diversity that are representative of the remaining wild population.

For more information on this project, please contact Dominique Sigg (telephone: 07 3346 9004 or e-mail: dsigg@zen.uq.edu.au ).

Figure 1. A fully grown male bridled nailtail wallaby (photo by Dominique Sigg)

Figure 2. Male nailtail, showing the distinctive bridle (photo by Dominique Sigg)

Figure 3. Mother and young at foot (photo by Dominique Sigg)

Figure 4. Claw-like nail on the tip of the tail, from which the species gets its name (photo by Dominique Sigg)

Figure 5. Former and current range of the bridled nailtail wallaby (click image for full map)