The Royal Society for the Protection of Birds announced the result of its annual Make Nature Count survey. More than 78,000 people participated during the first week of June, counting the birds and other species in their gardens.
The volunteers reported 12 percent more adult song thrushes than last year, a sign of good breeding conditions in 2011. Adult blackbirds, also in the thrush family, were spotted in 90 percent of all gardens.
But chicks were far less common. House martins, robins and swifts also appeared to have had breeding problems.
The society suggested the cold, damp spring hurt food supplies, leaving birds with less for their chicks, and parents may have had to spend more time searching for food, leaving chicks alone in their nests.
"Each of the 78,000 people involved in Make Your Nature Count has helped to give us data on a scale that just wouldn't be possible if we tried to collect it in any other way," said Daniel Haybow, conservation scientist for the RSPB. "It's really useful as a snapshot of how U.K. wildlife fared this summer and a number of species may have had a tough time in the cold and wet weather."
The society asked volunteers for the first time to count slow worms in their gardens, in an effort to get a baseline for future counts. The worms were found in about 10 percent of gardens, but they were spotted regularly in just 4 percent.