N. Gopal Raj Concern over the possibility that wild birds might transport the bird flu virus known as H5N1 has led to greater interest in studying bird migration. A flock of flamingoes over the Pulicat Lake in Andhra Pradesh. One day in December last year, Niranjan M., a 29-year-old engineer and avid bird-watcher living in Bangalore, drove some 125 km to a lake near Somnathpur in Karnataka. The lake was awash with a couple of hundred migratory birds, mostly bar-headed geese and, in the warm glow of the evening sun, he took over two dozen photographs. The bar-headed goose, distinguished by two dark bands on the back of its head, is a remarkable bird. If the Arctic tern is the natural world's champion long-distance migrator, each year travelling from high northern latitudes to as far south as the Antarctic and then back again, the bar-headed goose is the high-altitude expert. This goose is able to fly right across the Himalayas and over some of the world's tallest mountains. Mountaineers have spoken of seeing bar-headed geese flying over the summit of Mount Everest. In order to do so, the bird's biology has adapted to efficiently extract and utilise what oxygen is available in the thin air at such altitudes. In early 2000, scientists fitted a small satellite transmitter to a bar-headed goose at the Keoladeo National Park in Bharatpur, Rajasthan. They were then able to track it as it stopped along the banks of the Ganges before proceeding to cross the Himalayas in less than 24 hours to reach the Tibetan plateau. It was only when Mr. Niranjan looked closely at the digital photographs he had shot that he noticed that in one a single bar-headed goose had a yellow band around its neck with the letters