Europe has an estimated 421 million fewer birds today than it did 30 years ago, a study has found.
Around 90pc of the losses have affected the most common and widespread species including sparrows, skylarks, grey partridges and starlings.
Scientists believe the population crash can be linked to modern farming methods and deteriorating habitats.
Dr Richard Inger from the University of Exeter said: "It is worrying that the most common species are declining because it is this group of birds that people benefit from the most.
"It is becoming increasingly clear that interaction with the natural world and wildlife is central to human well-being, and significant loss of common birds could be quite detrimental to human society."
Not all common birds are declining. Populations of great tits, blue tits, robins and blackbirds, are all increasing.
Rare species such as marsh harriers, ravens, buzzards, storks and stone curlews had also shown increases in recent years.
The research, co-led by Britain's Royal Society for the Protection of Birds (RSPB), is published in the journal Ecology Letters.
The scientists analysed data on 144 species of European birds collected from numerous surveys in 25 countries.
Much of the information was provided by thousands of volunteer fieldworkers.