Everything about Island Restoration totally explained
The
ecological restoration of islands, or
island restoration, is the application of the principles of
ecological restoration to
islands and island groups. Islands, due to their isolation, are home to many of the world's
endemic species, as well as important breeding grounds for
seabirds and some
marine mammals. Their ecosystems are also very vulnerable to human disturbance and particularly to
introduced species, due to their small size. Island groups such as
New Zealand and
Hawaii have undergone substantial
extinctions and losses of
habitat. Since the 1950s several organisations and government agencies around the world have worked to restore islands to their original states; New Zealand has used them to hold natural populations of species that would otherwise be unable to survive in the wild. The principal components of island restoration are the removal of introduced species and the reintroduction of native species.
Islands, endemism and extinction
Isolated islands have always been known to have greater levels of endemism; since the
1970s the theory of
Island biogeography, formulated by
Robert MacArthur and
E.O. Willson this is understood to be because isolation limits immigration of new species to the island, allowing new species to evolve. For example, 71% of
New Zealand's bird species (prior to human arrival) were endemic. Island species, as well as displaying greater levels of endemism, have characteristics that make them particularly vulnerable to human disturbance.
Many island species evolved on small islands, or even restricted habitats on small islands. Small populations are vulnerable to even modest hunting, and restricted habitats are vulnerable to loss or modification. More importantly, island species are often ecologically naive, that's they've not evolved, or have lost appropriate behavioural responses to
predators. This often resulted in flightlessness, or unusual levels of
tameness. This made many species susceptible to hunting (it is thought, for example, that
moas were hunted to extinction in a few short generations) and to predation by introduced species. Some, such as the
Dodo, are thought to have become extinct because of the pressure of both humans and introduced animals. One estimate of birds in the
Pacific islands puts the extinctions at 2000 species. Between 40 to 50% of the bird species of New Zealand went extinct since
200 AD.
Island restoration
The field of island restoration is usually credited with having been started in New Zealand in the
1960s, but other smaller projects, such as the restoration of
Nonsuch Island in
Bermuda (which began in
1962) have been going on for almost as long. Nevertheless, the program undertaken by the
Department of Conservation (DOC) is one of the largest in the world. It began on
Cuvier Island, where ecologists removed stock,
goats,
feral cats and finally, in
1993,
Pacific Rats. The success of the project resulted in similar projects around New Zealand. The advantages to the DOC were considerable; in addition to protecting species endemic to smaller islands, like the
Magenta Petrel, islands near the mainland, once restored, could act as habitat for species of birds that were unable to survive on the mainland. Species like the
Takahe, where the remaining wild population was at considerable risk from feral cats and dogs, could be moved to these islands to safeguard the species.
Eradication of introduced species
One important aspect of island restoration is the removal of
invasive species. Since these species are most often the reason that native fauna and flora is threatened, their removal is essential to the restoration project. Islands are particularly suitable for restoration as once cleared of an introduced species they can be kept cleared of these species by virtue of being an island. Species removal is intensive and expensive, and methods used must be carefully chosen as to not create too much impact on non-target species. Feral cats, goats and three species of rats are among the most damaging species introduced to islands (Moors & Atkinson 1984). The differences in size, lifestyle and behaviour preclude the use of the same techniques for all of them, but with many species a range of techniques needs to be used in order to ensure success. Larger animals, such as goats and pigs, can effectively be hunted; in the case of
Round Island, in
Mauritius, all the goats were eliminated by a single marksman. On larger islands ecologists use a
Judas goat, where a radio collared goat is released into the wild. This goat is then followed and groups it joins are removed. To remove cats a combination of techniques is needed, both hunting, trapping and poisoning. Cats are more difficult to hunt than goats and pigs, requiring the use of experienced hunters and night hunting.
Trapping is ineffective for rats, given their sheer numbers, and the only method that works is
poisoning, which can be delivered into the field by broadcasting (by hand or from the air) or by the maintenance of bait stations. This method has been employed around the world, in the
Falkland Islands, in the tropical Pacific, and off New Zealand, where over 40 islands have been cleared. This method isn't without problems, especially if the rats share the island with other, native species of rodent that might take the bait as well, as has happened on
Anacapa Island in the
Channel Islands. In the Pacific poison intended for rats was taken by land
crabs instead; the crabs were not affected by the poison but frustrated attempts to clear the rats.
The removal of invasive
weeds is, in most cases, more difficult than removing animal species. One such eradication was that of
sandbur,
Cencrus echinatus, an introduced
grass on
Laysan. The grass, introduced to Laysan around
1961, had taken over 30% of the island by
1991, displaced the native
bunchgrass, and reduced the breeding habitat of two endemic threatened species, the
Laysan Duck and
Laysan Finch, as well as those of several
seabirds. The removal took ten years, with controlled spraying for the first year, then individual removal of plants, then, when few plants were being found, sifting of the sands around plants to remove seeds. The cost of the eradication was $150,000/year.
Restoration of former habitat
In many cases the removal of introduced species is sufficient to allow a return to a pre-disturbance state, but generally active management, often in the form of replanting native flora and reintroduction of expirated fauna is needed to achieve restoration goals. Planting of native species helps to replenish species that were either grazed or out competed. Species of animal can be translocated either from existing populations, or from captive bred populations. These reintroductions need to be carefully managed, particularly in the case of
endangered species, where the potential benefits need to be weighed against the possibility of failure. Not all translocations succeed, and it may be necessary to help the reintroduced animals along with supplementary feeding or other kinds of management.
One other important aspect of restoration is prevention, that is, keeping invasive species from returning to a cleared island. This can be achieved by restricting access to the island in question (reducing possible instances of invasion) to more stringent quarantine methods. For example, in order to prevent invasive weeds from returning to Laysan people working on the island must bring entirely new clothes to the island, which must be frozen prior to arrival.
Opposition to island restoration
Prior to the initial efforts to remove rats from New Zealand's offshore islands there was a great deal of skepticism as to the feasibility of island restoration amongst ecologists and conservation workers. However as the techniques have improved and larger islands have been restored, most of the initial criticisms from within the field have been dropped, in particular as the costs of eradication are often much lower than continuous pest control. Outside of the field of conservation there has been some opposition from other interested groups, particularly from the
animal rights movement, which contends that the
welfare of the pests in question isn't adequately addressed in island restoration plans. Because a broad spectrum of pest removal techniques needs to be used, including leg traps, animal rights campaigners accuse ecologists of cruelty, and indifference to non-targeted species that also take bait or are trapped, and suggest that more humane methods such as capture and
sterilization be used instead (something those working in island restoration contend would be too expensive). Some also defend the rights of the introduced species to exist as well. Others, including scientists affiliated with the animal rights movement, accept that when the choice is between the future of a species and a population of pests, the future of a species must take priority (with the caveat that the extermination is conducted as humanely as possible). Opposition to island restoration hasn't led to the abandonment of many projects but has delayed several, particularly through court action. Groups sometimes adopt different approaches; opponents of
hedgehog removal in the
Outer Hebrides offered bounties for live hedgehogs removed from the islands and relocated in their natural habitat. Invasive plants can also generate strong feelings. The removal of
Eucalyptus trees from
Angel Island in
San Francisco Bay faced considerable opposition.
Island restoration projects
Island restoration has been attempted in many countries since the 1960s, and has met with varying degrees of success. The following examples highlight some of the factors that influence projects.
Aleutian Islands
The
Aleutian Islands, prior to the 1700s, lacked any terrestrial predators, but from the mid 1700s
Arctic Foxes were introduced to act as a source for the
fur trade, a practice that continued into the early 20th century. This introduction decimated the birds of the chain, particularly
seabirds like the
Whiskered Auklet. The reduction in seabirds, in turn, had effects on the
ecology of the islands, as many of the plants were dependent on the guano from nesting birds acting as a fertilizer. In the early 1950s managers of the Aleutian Islands Reservation became aware of the damage, and an eradication program began. Since then over 80 islands have been cleared of non-native foxes (only six islands remain) and bird populations have rebounded. Whiskered Auklets, which numbered 25,000 in
1974, had increased to 116,000 in
2003.
Campbell Island
Campbell Island is a sub
Antarctic island 700 km south of New Zealand that became infested with
rats in the 1800s. Several endemic birds, including the
Campbell Island Teal and
Campbell Island Snipe, only survived on small rocky islets just off the island, and the populations were perilously low. Several teals were taken into captivity for
ex-situ conservation, but once they'd bred in captivity there was no-where else to return them to until the island was cleared of rats. The DOC's plan to remove rats from the island was one of the most ambitious attempted, as the island was so remote, the rat populations had the highest density of rats anywhere in the world, the weather treacherous and, at 113 km², it was the largest island at that point where eradication had been attempted. The poison had to be dropped in the winter, to minimize disturbance to nesting seabirds and reduce the chance of
bird strike for the pilots. After several experiments, the eradication began in
2001. In
2003 trackers with dogs were unable to find any rats. Soon after the island was cleared it was possible to return the teals to the island. Snipe have self-reintroduced to the island and have begun breeding.
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