One of the world's most dramatic wildlife rescues is coming to a successful conclusion on Tristan da Cunha in the South atlantic. Thousands of endangered northern rockhopper penguins, which were caught in thick oil slicks, have been saved in a month-long operation involving virtually all of the islands' 260 inhabitants.  The penguins were trapped in oil released by the freighter MV Oliva when it ran aground and broke up last month off Nightingale island, 20 miles from the main island of Tristan da Cunha. Thousands of these delicately feathered birds - known locally as pinnamins - were coated in thick oil and all would have died but for the extraordinary intervention of local people.  "Just about everyone on the island has played a part in this operation," Katrine Herian, an RSPB project officer based on the island, said. "It was an amazing, co-operative effort. Some people took boats to Nightingale to pick up oiled penguins - a very tricky task given the swells and winds there. Carpenters on the main island built pens to keep them in. The main store - where tools, cement and machinery are stored - was cleared out and sand put down on the concrete floor so we could keep the penguins there.  "Then the island's swimming pool was drained of nearly all its water and used as a home for cleaned birds. People even ransacked their freezers to find fish they could thaw out and use to feed the rockhoppers. They would have starved otherwise." In the end, about 4,000 rockhoppers were saved, although Herian warned that it was impossible to say how many others may have died: "We won't really know until next year when the birds start breeding again and we can get a proper chance to count numbers and see how badly they were affected."  The northern rockhopper penguin, Eudyptes moseleyi, is found on only a few islands in the atlantic, with 99% of its population making homes on the British overseas territory of Tristan da Cunha, a lonely, volcanic archipelago considered to be the world's most remote inhabited group of islands. There is no airstrip and the nearest major ports are in South africa.  Keeping track of the northern rockhoppers in such a location is not easy. Nevertheless, ornithologists have discovered that their numbers have plunged by more than 90% since the 1950s, with factors such as climate change and over-fishing of squid and octopus - the penguins' main source of food - being put forward as possible causes. as a result, the northern rockhopper is now classified as an endangered species. The wrecking of the MV Oliva, therefore, posed a significant threat to them. The ship was carrying 65,000 tonnes of soya beans from Brazil to China when it ran aground on 16 March on an islet off Nightingale island. all 20 crewmen were rescued by islanders, but the vessel broke apart and released more than 1,500 tonnes of oil on to the waters around the island, coating the rockhoppers.  Within a day, islanders and RSPB workers began their remarkable rescue operation. When winds and the swell were low, they sailed to the island in small boats and, using Tristan's principal fishing vessel, the Edinburgh, as a command vessel, began shipping oiled rockhoppers back to the main island.  "The birds get very distressed when they are coated in oil," said Herian. "They lose body temperature very quickly in the water and preen themselves to get rid of the oil.