The population of house sparrows in Britain has fallen nearly 70 percent in the last 30 years as a trend for paving over gardens and removing trees has left too few insects for them to eat, the RSPB said today.

The sparrow has almost completely vanished from central London and numbers are well down in cities like Bristol and Edinburgh.

"The trend towards paving of front gardens and laying decking in the back, and the popularity of ornamental plants from other parts of the world, has made many gardens no-go areas for once-common British birds," said Will Peach, from the RSPB.

The changes mean there are too few insects in summer, leaving young house sparrows in towns and cities starving in their nests. The number of house sparrows in Britain has declined 68 percent since 1977.

An RSPB study monitored house sparrows in Leicester and surrounding villages and found that the number of birds dropped 28 percent over three years, with many chicks dying within four days of hatching.

"Each pair of house sparrows must rear at least five chicks every year to stop their numbers falling," said Peach, "But in our study, too many chicks were starving in their nests... Young house sparrows need insects rather than seeds, peanuts or bread to survive."

The research, published in the journal Animal Conservation, found chick survival was higher in areas where insects, such as aphids, were abundant.

"This study highlights the importance of using native varieties of plants in our urban green spaces which, in turn, support large numbers of insects that are important in the diet of house sparrows," said Phil Grice, an ornithologist at Natural England.

Peach added: "Many of the things we can do to help just mean being lazy, doing nothing and allowing the garden to be a bit scruffy."