Cavity Wall Nesting Boxes provide the ideal nesting and roosting solution for many of our UK and visiting small to medium cavity nesting birds. House sparrow numbers were not monitored adequately before the mid-1970s. Since then, numbers in rural England have nearly halved while numbers in towns and cities have declined by 60 per cent. Because of these large population declines, the house sparrow is now red-listed as a species of high conservation concern. Our Cavity Wall Nesting Box will fit almost any cavity wall arrangement (typically 100mm), however, with small adjustments to the building brick / block or render, all situations can be accommodated.