A study of 144 bird species across 25 European countries has shown that bird populations have declined sharply over the past 30 years. The biggest declines are in the most common species, while some rarer species have shown increase.

The study was conducted by the University of Exeter, UK, the Royal Society for Protection of Birds (RSPB) and the Pan-European Common Bird Monitoring Scheme (PECBMS) and it was published in the journal Ecology Letters.

The study says that over 421 million individual birds were lost over 30 years. Around 90 percent of these losses were from the 36 most common and widespread species, including house sparrows, skylarks, grey partridges and starlings.

"It is very worrying that the most common species of bird are declining rapidly because it is this group of birds that people benefit from the most," said Richard Inger of the University of Exeter, in a statement.

"It is becoming increasingly clear that interaction with the natural world and wildlife is central to human wellbeing and significant loss of common birds could be quite detrimental to human society."

Birds provide multiple benefits to society. They help to control agricultural pests, are important dispersers of seeds, and scavenging species play a key role in the removal of carcasses from the environment. In addition, for many people birds are the primary way in which they interact with wildlife, through listening to bird song, enjoying the sight of birds in their local environment, feeding garden birds and through the hobby of bird watching.

The majority of the declines can be attributed to considerable losses from relatively few common birds, but not all common species are declining. Numbers of great tits, robins, blue tits and blackbirds were all shown to be increasing. Populations of rarer species, including marsh harriers, ravens, buzzards and stone curlews have also shown increases in recent years: this is likely to be the result of direct conservation action and legal protection in Europe.

"This is a warning from birds throughout Europe. It is clear that the way we are managing the environment is unsustainable for many of our most familiar species," RSPB's Richard Gregory said.

Conservation efforts tend to be focused on rarer species but the research suggests that conservationists should also address issues affecting common birds, for example those traditionally associated with farmland. The decline in bird populations can be linked to modern farming methods, deterioration of the quality of the environment and habitat fragmentation, although the relative importance of these pressures remains unclear.

The study brought together data from many thousands of individual surveys in 25 different countries, highlighting the value of the different national monitoring schemes increasingly working together. The researchers suggest that greater conservation funding and effort should be directed to wider scale environmental improvement programmes. These could include urban green space projects, and effective agri-environment schemes, which, informed by lessons learned from past schemes, should aim to deliver real outcomes for declining bird species whether they are rare or common.