Urbanization and climate change may be partly to blame for a serious decline in Britain of house sparrows, formerly the most common bird in the country. Max Nicholson, a 96-year-old bird watcher who has been conducting informal bird censuses for 75 years, said that this year he counted only eight sparrows in London’s Kensington Gardens, compared to 2,603 spotted in the gardens in 1925. According to the British Trust for Ornithology, the population of house sparrows in the British countryside declined by about 50 percent between 1973 and 1997; in London, there has been an even more dramatic drop of 53 percent between 1994 and 1999. On Monday, British Environment Minister Michael Meacher announced that the government will study the possible causes of the sparrow downswing, and London Mayor Ken Livingstone has made protection of the sparrow a goal for the city.