Endangered Species Handbook

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Vanishing Species

Actions and Attitudes: Page 9

     The elimination of introduced animals, from goats, cattle and pigs to cats and exotic plants, has been carried out on many islands and island-like environments around the world to preserve native species on the brink of extinction.  The governments of Australia and New Zealand, in particular, have rescued a number of critically endangered species.  Lord Howe Island, located off the northeastern coast of Australia, once harbored diverse wildlife.  After settlement, and introduction of rats and other exotic species, forest clearance and other threats, numerous extinctions of native animals occurred, and most of its surviving species are endangered.  Efforts on the part of the government to return the island to its near-original state, with total protection of the remaining tropical forests, coral reefs and other habitats, is underway.  Ecotourism has been developed on the island, but the number of visitors is kept at a level that will not harm the island's endemic fauna and flora.  Cats may not be kept by the limited number of residents as pets because of their threat to native birds, and exotic animals are being eliminated from the wild.  The endangered, flightless Lord Howe Rails (Gallirallus sylvestris), highly vulnerable to predation by cats and other predators, are now gradually increasing with strict protection.  Once found throughout the island, these rails became restricted to mountain areas after they were eliminated by feral pigs, goats, cats, dogs and the introduced Masked Owl (Tyto novaehollandiae) elsewhere on the island.  Captive breeding has been successful, and after work to eliminate exotic animals, these rails were reintroduced to several of their original habitats at lower elevations (BI 2000).  The population numbers about 130 birds, with a potential living space for up to 220 birds (BI 2000).
     In some cases, control programs for exotic species on islands are not done humanely.  Wire snares and poison have been employed rather than live-catch traps, for example.  Humane organizations should be consulted by governments to employ humane methods in ridding islands of non-native animals.
     The Black Robin (Petroica traversi), a beautiful songbird resident on the Chatham Islands off New Zealand, numbered just five birds in 1980, with only one breeding pair (BI 2000).  Rats and cats colonized the island after settlement, and deforestation had destroyed the species' habitat.  A tree-planting project in which 120,000 trees were planted on Mangere Island, one of its prime habitats, was undertaken (BI 2000).  Supplemental feeding and nest protection from introduced Starlings (Sturnus vulgarus) and seabirds, which were preying on them, helped somewhat.  Real progress began with the use of an unusual program in which eggs of the Black Robin were placed in the nests of other species to raise them and allow the original female, who became known as "Old Blue" and lived 12 years, to lay more eggs.  Birds of a related species, the Tomtit (Petroica macrocephala), raised these robins, and chicks were successfully reintroduced to Mangere Island (BI 2000).  Such cross-fostering has failed with species such as the Whooping Crane, whose eggs were cross-fostered to Sandhill Cranes, because the chicks when mature, tried to mate with Sandhill Cranes instead of members of their own species, having become imprinted.  In this case, the chicks bred with members of their own species, and numbers rose to 259 in 2000 (BI 2000).  They were all descended from the original pair of birds.  The New Zealand Department of Conservation, which had overseen the breeding program, found through DNA studies that the birds are nearly identical genetically (Hutching 1997).  Further studies will attempt to discover immune responses and other signs of inbreeding, but outwardly, these robins are thriving, with a 70 percent survival rate and normal fertility (Hutching 1997).  Species with such low genetic variability tend to be extremely vulnerable to extinction, having little ability to adjust to changes in their environment or food supply.

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