Threatened seabirds: rat eradication on the South Barnard Islands
Sooty oystercatcher (Photo: DERM)
Introduction
When seabirds nest, the adults, their young and eggs are vulnerable to predation by introduced predators. The introduced predator that is often the greatest threat on islands is the black rat (Rattus rattus) – a voracious nest predator. On the South Barnard Islands near Innisfail, the then Environmental Protection Agency undertook a rat eradication program that has safeguarded the nests of many seabird species, including the Endangered little tern (Sternula albifrons) and the Near Threatened sooty oystercatcher (Haematopus fuliginosus).
Introduced species
The arrival of Europeans in Australia also saw the arrival of a wide range of non-native species, including the cow, sheep, pig, cat, fox and rat. The black rat would have been one of the first animals to arrive with the early European ships in the late 1700s. While many introduced species allowed settlers to maintain farming methods from their countries of origin, all have impacted on their new environment in some way, and some introduced species have had significant adverse impacts on many species of native wildlife.
Sensitive island ecosystems
Islands, because they are usually small in size, are particularly sensitive ecosystems. Any additions or changes to island environments can often have lasting effects on their ecology. The isolated nature of islands can affect the recovery of their ecosystems after change, particularly as the distance between islands and mainlands often inhibits dispersal of native species. But this distance can also provide islands with protection, acting as an effective barrier against introduced species. Islands typically provide important nesting sites for many species of seabirds, including important migratory and threatened species.
The South Barnard Islands
The South Barnard Islands are located approximately 25km south of Innisfail, and consist of Sisters Island (3.5ha) and the larger Stephens Island (10.5ha). They are one of the most important nesting sites in the northeast of Queensland for the bridled tern (Onychoprion anaethetus), as well as a nesting site for other seabirds. It is not known exactly when and how black rats arrived on these islands, but they were first identified from surveys conducted in 1999. Floods from nearby river systems may have washed the rats to the islands that lie about 5km from the mainland. The rats soon began invading seabird nests and eating eggs. Because of their high potential to devastate the island's seabird population, an eradication program was implemented.
Recovery actions
- The rat eradication program began in 2000. An extensive survey of rat numbers was undertaken and gave staff an opportunity to confirm that there were no other terrestrial mammals present on the islands. As there were no other mammals on the islands, poisoned baits were used to combat rats.
- Following baiting, several surveys were undertaken on the islands to check for the presence of rats. Rats are no longer known to occur on the islands.
- Although the program has been a success, rats may return to the islands, especially since the origin of their arrival remains unknown. The Department of Environment and Resource Management continues to monitor the islands for rats.
Last updated 18 April 2011