Nesting skua. Photo by E. Woehler

Critically, Heard Island and the McDonald Islands (HIMI) are free from introduced predators, and provide crucial breeding habitat in the middle of the vast Southern Ocean for many species of seabirds.

The potential introduction of rodents is considered the single biggest risk to the seabirds on Heard Island.

The impacts of a range of biological invasions on other Southern Ocean Islands have been significant, including devastation of seabird breeding populations, modification of plant communities, changes to invertebrate communities, reduced biodiversity and local extinctions. Such invasions would likely have similar impacts at HIMI.

There are currently only two animal species at Heard Island considered to be 'aliens' (non-natives) : a thrip Apterothrips apteris and a mite Tyrophagus putrescentiae. Heard Island has, however, been exposed in the past to introduced species which have not persisted, probably due to the harsh climate (for example silverfish, house flies, clothes moths, sheep, cockroaches and a rat).

Climate warming has been observed in the HIMI region, and is likely to increase the probability of alien species establishing. It may also enhance the adverse impacts alien species that do arrive.