A tiny bird which visited the Mai Po Marshes in 1990 has turned up seven years later and 3,000 kilometres away in Japan. 'This is the fifth Great Reed Warbler which we have marked at Mai Po and has subsequently been recorded in Japan,' said the World Wide Fund for Nature's Hong Kong executive director David Melville. 'There have also been four Great Reed Warblers marked in Japan which we have later caught at Mai Po,' he said. Bird-ringing allows experts to chart the migration routes of birds which fly thousands of kilometres to their breeding and wintering sites. Mr Melville said Great Reed Warblers passed through the territory in spring and autumn, stopping off at the Mai Po Marshes nature reserve. The birds, which depend on wetlands where they build nests in the reeds, breed in northern China, Japan and Korea. They spend the winter in southeast Asia. The Great Reed Warbler found in Japan weighed 30 grams, and Mr Melville said they fed voraciously on insects in the reedbeds, gaining up to 1.4 grams a day in weight. 'We have some here which are incredibly fat,' he said.