Re-introduction is used as a wildlife management tool for the restoration of an original habitat when it has become altered or species have become extinct due to over-collecting, over-harvesting, human persecution, or habitat deterioration. An example of a successful translocation was the one performed with the plant Narcissus cavanillesii to prevent its flooding due to the construction of a dam. Lastly, the third type of translocation is re-stocking. Re-stocking is the translocation of an organism into the wild into an area where it is already present. Re-stocking is considered as a conservation strategy where populations have dropped below critical levels and species recovery is questionable due to slow reproductive rates or inbreeding. The World Conservation Union recommends that re-stocking only occur when the causes of population decline have been removed, the area has the capacity to sustain the desired population, and individuals are of the same race as the population into which they are released but not from genetically impoverished or cloned stock. Between 1973 and 1989 an estimated 515 translocations occurred per year in the United States, Canada, New Zealand and Australia. The majority were conducted in the United States. Birds were the most frequently translocated, followed by threatened and endangered species, then non-game species. Of the 261 translocations in the United States reported wild species were most frequently translocated, and the greatest number occurred in the Southeast. Western Shield, of Australia, is a nature conservation program which plays an important role in protecting Australia’s native animal population. More importantly, Western Shield also has programs specializing in translocation of endangered and threatened animals. Founded in 1996, it's the most successful wildlife conservation program in Australia and in 2006, it still remains among the largest in the world. The program has already had significant success: three native mammals in Australia – the woylie, quenda and tammar wallaby – have been removed from the threatened species list, many populations of native animals have recovered or been re-established in their former ranges, and the restoration of ecological processes has begun. From 1996 to 2000, Western Shield has taken part of 60 translocations, mostly introductions, of 17 species all over the country on private and interstate lands. Species translocation can vary greatly across taxa. For instance, bird and mammal translocations have a high success rate, while amphibian and reptile translocations have a low success rate. Successful translocations are characterized by moving a large number of individuals, using a wild population as the source of the translocated individuals, and removing the problems which caused their decline within the area they are being translocated.