House sparrow numbers could be hit by the building of new homes on existing urban gardens as they prefer residential areas to parks in towns and cities, research suggests.
Nesting house sparrows select houses with gardens over all other habitats in urban areas, including green spaces such as parks and allotments, according to a study by the British Trust for Ornithology (BTO).
The trust said many of the green areas in towns and cities are unsuitable for the threatened species as parks tend to be open habitats without the scrubby cover the birds like and offer few nesting opportunities.
Urban gardens tend to have shrubs in which the sparrows can gather, as well as bird boxes and cavities under roof tiles for nesting in.
The findings suggest that “garden grabbing”, or building on gardens, is likely to be highly detrimental to the species, which has seen numbers tumble by more than 70% since the 1970s and is now red-listed because of concerns about its future.
The declines have been particularly marked in urban areas, where pollution, the number of insects for food, predators and the availability of nest sites are all thought to be affecting populations.
Last year, the Government promised a crackdown on the practice of garden grabbing, which saw the number of houses being built on gardens rise from one in 10 to a quarter of new properties between 1997 and 2008.
The BTO study called for planners to limit development on gardens where sparrows are present as part of efforts to improve garden habitats, as well as preserving good quality green spaces and brownfield sites.
Mike Toms, BTO head of garden ecology, said: “Understanding the importance of urban gardens for house sparrows means that we can advise planners and developers on how to retain and encourage house sparrow populations within our changing urban landscape.”
The BTO said householders could encourage house sparrows into their gardens by planting shrubs such as cotoneaster and berberis, and putting up nest boxes which are suitable for sparrows, with a 32mm (1.25in) diameter entrance hole.
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