House sparrows were once among Britain's most familiar birds. Their dramatic decline in urban areas since the 1970s reflects deep changes to the built environment and food availability.
House sparrow decline reflects cumulative welfare pressure at the population level: insufficient insect food for chicks leads to starvation in early life, lack of nesting cavities forces colonial breeders into marginal sites, and urban food environments provide poor nutrition for adults. Individual birds experience these pressures as failed breeding attempts, chick mortality, and reduced body condition through winter.