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.