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

Abstract

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 abundant in coastal areas all around the island. The distribution of rat populations is divided into discrete units by the availability of suitable habitat which, in turn, is a consequence of the rugged topography, particularly on the 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 ®rmly occupy a habitat niche in an environment where food is plentiful, predators are few and interspeci®c competition minimal. The principal habitat, tall Poa foliosa tussock grassland, provides year-round shelter and food. Rats dig burrows in the peaty stools of the tussock plants and construct nesting chambers at the base of the dense leaf canopy. Predictably, this provides a warmer and more stable thermal environment than that experienced outside under the tussock canopy where the runs are located. Tussock grasslands are spreading under the in¯uence of management control measures directed at the introduced European rabbit and possibly global warming. Management programmes are also directed towards the eradication of feral cats. In response, rat populations may be expected to expand in numbers and to occupy new territories. Without control this may, in the long term, have serious consequences for the island's avifauna, particularly the smaller, burrow-nesting species.

The impact of introduced ship rats (Rattus rattus) on seedling recruitment and distribution of a subantarctic megaherb (Pleurophyllum hookeri)

“…They have previously been recorded from close to the shoreline up to an altitude of 250 m a.s.l. and up to 1 km inland (Copson 1986;Pye et al . 1999).…”

“…In 2000 we observed rats from below the high tide line to 280 m a.s.l. Their major habitat is coastal tall tussock grasslands where they feed predominantly on shoots of Poa foliosa (Copson 1986;Pye et al . 1999;Copson & Whinam 2001).…”

“…Our results confirm that rats returned to the caches throughout the winter. Attendance at caches declined during spring, coinciding with the emergence and expansion of new P. foliosa shoots (Ashton & Jenkin 1965;Jenkin & Ashton 1970), which are the preferred food of rats on Macquarie Island (Copson 1986;Pye et al 1999).…”

“…Pleurophyllum hookeri herbfields have not been identified as rat habitat on Macquarie Island prior to this study. The predominant rat habitat is tall tussock grasslands, where they breed by creating burrows in the peaty tussock pedestals (Pye 2000). The mean home range of breeding rats in tall tussock grassland is 0.114 ha (Pye 2000).…”

“…1989;Crafford 1990;Hunter 1990;Smith & Steenkamp 1990;Chown & Smith 1993;Scott 1995;Huyser et al . 2000;Pye 2000;Chown et al . 2001;Copson & Whinam 2001;Pontier et al .…”