House sparrow populations have declined by 71% in the UK since the 1970s. Urban renovation, loss of nesting holes in buildings, reduced garden insect availability, and changes in urban green space management have driven city populations to near-extinction in some areas.
House sparrow chicks that cannot access adequate insect food in dense urban areas starve in the nest while adults make repeated unsuccessful foraging trips. Loss of nesting holes from renovated buildings prevents colonisation of new urban areas. The species highly social behaviour means that small isolated urban populations face additional stress from reduced flock size and inability to find mates.