House sparrow numbers have fallen by 68% in London since 1994
Twenty parks and beauty spots across London are to have wild grass and flowers planted in them to attract fast disappearing house sparrows.
More traffic, a loss of green spaces and the paving over of city gardens are being blamed for the birds' numbers falling by 68% in 15 years.
The RSPB has warned that sparrows may disappear altogether if sanctuaries are not built in the city.
The scheme, which will cost £170,000, is being funded by the SITA Trust.
The trust manages money raised through taxes on rubbish sent to landfill.
Tim Webb, spokesman for the RSPB, said patches of wild grass and flowers in beauty spots would attract insects, which in turn will draw sparrows to feed.
"In Greater London sparrow numbers are down 68% on what they were in 1994, and there are some parts of central London where you don't see them at all any more," he said.
"There has been a dramatic decline and the concern is that the population will reach a level where it is no longer sustainable and they will disappear completely."
Mr Webb added that wild patches in parks, including Hampstead Heath, Tooting Common, Primrose Hill and Leyton Marshes, will also boost the butterfly and moth population.
The three-year scheme will be supported by Lee Valley Regional Park Authority, City of London, the Royal Parks Agency, Wandsworth Borough Council, Islington Council and Southwark Council.