stood at only 111 people. Just 16 years later the
Chilean government annexed the island, and it
became in effect a sheep ranch, with the remaining
islanders confined to a single village as forced
labour.
The islands of the Pitcairn group lie between 23.9
and 24.7S and 124.7 and 130.7W in the South
Pacific Ocean, and consist of volcanic Pitcairn
Island, the raised coralline Henderson Island, and
the small coral islands of Ducie and Oeno atolls.
Pitcairn is of special historical interest, owing to its
occupation by the HMS Bounty mutineers, in
AD1790, but before that it was occupied and then
abandoned by the Polynesians. Although the pre-
cise timing of the settlement of Pitcairn by the
Polynesians remains problematic, it now appears
that Henderson Island was settled between AD 800
and 1050 and deserted some time after AD 1450
(Benton and Spencer 1995). During the occupation,
marine molluscs, turtles, and birds were heavily
predated. Settlement was accompanied by the
introduction of cultigens and tree species, and by
burning for crop cultivation. A number of endemic
bird species and at least 6 out of 22 land-snail
species became extinct during this period. It seems
likely that sustained occupation was only possible
through interaction with Pitcairn and, 400 km to
the west, with the island of Mangareva.
Weisler (1995) has outlined a prehistory of
Mangareva, which suggests a similar pattern of
resource exploitation and environmental depletion
as Easter Island. Mangareva experienced high
human population levels, depleting the resource
base to the point where they could no longer sup-
port long-distance voyaging, dependent as it was
on large ocean-going vessels, skilled crews, food
supplies, and exchange commodities. As on Easter
Island, the requirement for large trees for canoe
manufacture does not appear to have been matched
with sustainable tree husbandry! Thus, according
to Weisler’s reconstructions, the overexploitation of
resources by these linked communities resulted in
the severing of voyaging linkages and the eventual
abandonment of the most marginal locations,
including both Henderson and Pitcairn. With its
poor soils, sporadic rainfall, lack of permanent
sources of potable water, karstic topography, and
low diversity of marine and terrestrial life, it is
pretty remarkable that Henderson was settled by
the Polynesians in the first place (see illuminating
discussion in Diamond 2005).
The Henderson petrel (Pterodroma atrata), only
recently described as a distinct species, breeds
exclusively on Henderson Island. A study in
1991/92 showed that its breeding success was
greatly reduced by predation by the Pacific rat
(Rattus exulans) and the species was judged to be
threatened (Benton and Spencer 1995). It has been
calculated that this petrel has been undergoing a
slow decline since the Polynesians introduced the
rat some 700 years ago, and it is possible that this
may continue until the petrel becomes extinct,
although this would seem a remarkably long lag
time for a new ‘equilibrium’ to be reached.
Henderson Island has four surviving endemic land
birds, including one fruit dove, Ptilinopus insularis.
In the past, this dove shared the island with at least
two other Columbiformes: Gallicolumba, a ground
dove, and a Ducula pigeon. The dove became
extinct during Polynesian occupation about the late
thirteenth century. Indeed, five of Henderson’s nine
endemic land birds became extinct as a result of this
occupation, as did most of the small ground-nest-
ing seabirds (Wragg 1995). Human predation, as
well as predation by (and competition with) the
commensal Pacific rat, and habitat alteration by
people, each had a role in these changes in the avi-
fauna. The process of change is ongoing, and today
a number of the endemic land snails of Pitcairn
appear to be restricted to remnants of native vege-
tation of only about 1 ha or less. These stands are
currently under great threat from the spread of
invasive exotic plants, which cast a deep shade and
create an understorey inimical to the snails (Benton
and Spencer 1995).Indian Ocean birds
As shown in Table 11.3, the islands of the Indian
Ocean have also suffered significant losses of birds
in prehistoric and historic times. Most notably, on
Madagascar, 6–12 species of ratites became extinct,
almost certainly as a result of the arrival of the
Malagasy people. These losses included the largest312 ANTHROPOGENIC LOSSES AND THREATS TO ISLAND ECOSYSTEMS