Threatened Species - The Recovery of the Greater Stick-nest Rat
The Biology and Recent History of the Greater Stick-nest Rat Leporillus conditor
At the time of European settlement two species of Stick-nest Rats existed in Australia; the Greater Leporillus conditor and Lesser Stick-nest Rat Leporillus apicalis. These small rodent species (approx 300 gms) inhabited much of the semiarid and southern arid zone of Australia (view map) and were named after the conspicuous stick-nests they built, and lived in. Since European settlement both species were severely affected by the overgrazing of their preferred habitat types, the chenopod shrublands by rabbits and sheep. While both Stick-nest Rat species are believed to have become extinct on the mainland as recently as the 1930s, fortuitously, a single population of Greater Stick-nest Rats survived on the Franklin Islands, off the coast of Ceduna, South Australia. As a consequence of its extinction from the mainland and it's extremely restricted distribution to two small islands, the species was listed in the 1980s as endangered and a recovery plan was prepared and is being implemented. Unfortunately, the Lesser Stick-nest Rat is now presumed extinct. Recovery Plan
During the 1980s detailed studies of the rat's habitat and dietary requirements were carried out on the Franklin Islands and this information was used to develop a recovery plan for the species. The recovery targets identified were to:
Successful husbandry of a captive rat population at Monarto provided sufficient rats to found several new populations. These include populations on Salutation Island (Western Australia), Reevesby and St Peter Islands (South Australia), as well as in the fenced exclosure at the Arid Recovery Project at Roxby Downs (South Australia).The paragraphs below summarise some of the results obtained from each of these releases across the previous distribution of the Stick-nest Rat. Salutation Island and Heirisson ProngA single release of 40 Stick-nest Rats (18 male; 22 female) was conducted in July 1990 at Salutation Island. Annual monitoring has been conducted since 1990 and results have indicated the rats to be well established across the island, with recent increases in population size. Conservative estimates suggest this population to consist of between 900 and 1,000 rats. More recently, a release of Stick-nest Rats was conducted in a fenced area known as Heirisson Prong adjoining Salutation Island on the mainland, but no results are available at this time. Reevesby Island
A feral cat eradication program was implemented on Reevesby Island in 1985. The last feral cat was captured in March 1990. The first release of 16 stick-nest rats (7 male; 9 female) occurred in September 1990. A total of 101 Stick-nest Rats (51 male; 50 female) were released between September 1990 and September 1991. Annual monitoring has been conducted since 1991. Although slow to increase, more recently this population has shown an exponential "boom" phase, typical of many rodent species. During the population "boom" several native plant species on the island showed signs of overgrazing. Results from the April 2000 monitoring trip suggest that the rats' population size has decreased, and may now be stabilising at a more sustainable level. Current estimates suggest this population may number between 1,000 and 5,000 individuals. St Peter IslandSt Peter Island is relatively large (4,028 ha), and historically remained free of introduced predators. However, it has extant populations of Black Tiger Snakes and Sand Goannas. 20 stick-nest rats (8 male; 12 female) were first released on this island in June 1993. An additional 133 rats (63 male; 70 female) were released between 1993 -1998. Annual monitoring has been conducted since 1993, and results suggest that this population has been much slower to multiply than other populations, and has not shown the exponential "boom" observed on Reevesby Island. This may be because of the highly dispersed nature of the population across this island, and the potential effect of predation by snake and/or goanna. Although capture rates remain low, the tracks of stick-nest rats have been regularly observed over most of the island. Population estimates remain difficult to calculate, but there are expected to be at least 1,000 rats present. Roxby DownsAfter the successful construction of a vermin-proof fence enclosing 1,400 ha at Roxby Downs, and the eradication of all rabbits, foxes and cats within the exclosure,a trial reintroduction of 10 rats (5 male; 5 female) was conducted in September 1998. After initially promising results, a further 100 rats (52 male; 48 female)were released during 1999. Although relatively recent, this population remains extant, with new young being recruited into the population. The predation of Stick-nest Rats by resident Sand Goannas may slow the growth of this population,however, monitoring suggests that the population has more than doubled overthe first two years. Summary of Recovery Efforts
Program Support
AuthorsPeter Copley, Senior Ecologist, Threatened Species, Department for Environment and Heritage ContactPeter Copley, Senior Ecologist, Threatened Species, Department for Environment and Heritage |
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