islands, introduced rats Rattusspp., feral cats Felis catus, Small Indian Mongoose
Herpestes auropunctatus, Stoat Mustela erminea, Mink M. vison, foxes Vulpes, and
Alopexall are potential problem species (Merton 1978).
On mainland or continental areas, predator control is usually a localized or
a short-term option where it is best focused around areas where the focal species is
most vulnerable, that is, nest-sites, roost sites, feeding areas, supplementary feeding
stations, and release sites. Long-term predator control over large areas is usually not
sustainable. However, in New Zealand biologists are experimenting with managed
areas of up to 6000 ha in which smaller core areas are intensively managed. These
areas are termed “Mainland Islands.” Within these areas large herbivores are shot
from helicopters and the exotic rats and Brushtail Possums Trichosurus vulpeculaare
controlled by the aerial distribution of toxic baits, and in the intensively managed
areas trapping grids are set for exotic mammals including mustelids and feral cats.
Mainland Islands have been successful in providing secure habitat for a range of
native species and numbers of kiwi Apteryxspp. and Kokakos Callaeas cinereahave
increased (Innes et al. 1999). A more sustainable long-term option is to eradicate
exotic predators on islands, which can then be used as reintroduction sites for endan-
gered bird species (see Translocations) or to enclose areas in predator proof fences.
Approaches available include close guarding, the provision of safe nest-sites,
predator guards around nest trees, and the placement of supplemental feeding,
and release sites in safe fenced locations. An advantage of close guarding is that it
may reveal unknown predation problems. The first young Mauritius Kestrels
released spent time on the ground, where they were susceptible to mongoose and
cat predation, which explained losses of up to 25% of young at some sites. A close
guarding and trapping program around some nest-sites and most release sites
reduced the losses to these predators ( Jones et al. 1991, 1995; Cade and Jones 1994).
The removal of introduced predators from islands may allow native birds that
still exist to recover rapidly. On Little Barrier Island, New Zealand, fewer than
500 Stitchbirds Notiomystis cinctaremained, but after the eradication of cats the
population recovered within a few years to 3000 (Veitch 1985). Similarly on
Raratonga in the Cook Islands, the endemic flycatcher Pomarea dimidiata
declined to 29 birds in 1989, due primarily to nest predation by Black Rats Rattus
rattus. Rat control with poison laid out on a grid system throughout the habitat,
together with rat-proofing of nest-trees with predator guards, resulted in an
increase in the population to 189 over the next 10 years (Bell and Merton 2002).
The Aleutian Canada Goose Branta canadensis leucopereiadeclined after
Arctic Foxes and Red Foxes Vulpes vulpeswere introduced to the islands where
they bred. The breeding geese were reduced to just one fox-free island.
Broad population management approaches| 279