In a disturbing new study with overtones of Rachel Carson’s famous environmental book “Silent Spring,” a group of scientists from the United Kingdom and the Czech Republic report a stunning decline in the number of Europe’s birds since 1980. The birds that have vanished are members of the most common species such as sparrows, starlings and skylarks. The researchers calculate that there are now 421 million fewer birds across 25 European countries than there were at the start of the 1980s – a change the study attributes to human-caused environmental degradation.

The scale of decline, in the words of the study recently released in the journal Ecology Letters, is “alarming.” The research finds that of the 144 most common species, there were about 2.06 billion birds in Europe in 1980 and just 1.64 billion in 2009 (the most recent year considered in the study). Thus, the loss of 421 million represents more than a 20 percent decrease.

“Ninety percent of that decline can be attributed to the 36 most common species,” says lead study author Richard Inger of the University of Exeter’s Environment and Sustainability Institute. According to Inger, the top five species experiencing stark declines are the house sparrow, common starling, Eurasian skylark, willow warbler and Eurasian tree sparrow.

The research builds on thousands of bird surveys that have been carried out by volunteers going back to 1980. Surprisingly, the research finds that many rarer or endangered species (including marsh harriers and white storks) are increasing in number, perhaps in part because these birds have been successfully protected by conservation measures. But the loss of common birds, the study emphasizes, can have dramatic consequences, because by their very numbers, they have crucial roles to play in ecosystems, such as controlling the volume of pest species.

The study also notes that because these declines are in common species, they are more likely to be indicators of environmental degradation. “Common species are widespread and their numbers are linked to the deterioration of the quality of the environment on a landscape scale,” the paper notes. Inger says that he suspects expansion of agriculture represents a key cause of the decline, but so does urbanization. More farmland and more houses and roads means less habitat for birds and more habitat fragmentation.

“It’s a bit of a wake-up call,” Inger says.