House sparrows have experienced a rapid recent decline, particularly in urban and suburban environments: greater London lost seven out of 10 sparrows between 1994 and 2001. The causes remain largely unknown, with everything from cats to air pollution being blamed

75 research sites across Greater London looking into their seriously declining numbers.
House sparrows are being lost at an unprecedented rate. In some parts of London, where 'Cockney' sparrows were once a familiar sight, they may disappear altogether unless swift action is taken to prevent it.
Once a common bird in our towns and cities, studies of house sparrows have shown that their population has more than halved in the last 25 years