Distribution and habitat use of the feral black rat (Rattus rattus) on subantarctic Macquarie Island

Macquarie Island is the southernmost limit to the distribution of the black rat Rattus rattus. The species was introduced to this subantarctic island by sealers during the 19th century. The rats are now widespread and abundan t in coastal areas all around the island. The distribution of rat populatio ns is divided into discrete units by the availability of suitable habitat w hich, in turn, is a consequence of the rugged topography, particularly on t he west coast. Rats are found from almost sea level to 200-250 m a.s.l. and up to 1 km inland. They have adapted successfully to the rigorous climate and firmly occupy a habitat niche in an environment where food is plentiful , predators are few and interspecific competition minimal. The principal ha bitat, tall Poa foliosa tussock grassland, provides year-round shelter and food. Rats dig burrows in the peaty stools of the tussock plants and constr uct nesting chambers at the base of the dense leaf canopy. Predictably, thi s provides a warmer and more stable thermal environment than that experienc ed outside under the tussock canopy where the runs are located. Tussock gra sslands are spreading under the influence of management control measures di rected at the introduced European rabbit and possibly global warming. Manag ement programmes are also directed towards the eradication of feral cats. I n response, rat populations may be expected to expand in numbers and to occ upy new territories. Without control this may, in the long term, have serio us consequences for the island's avifauna, particularly the smaller, burrow -nesting species.