They always seemed such insignificant little birds, sparrows.

Back in the 1970s and 80s they were ubiquitous wee brown creatures that were part of the backdrop of daily life. To a child's eyes, they lacked the Vegas glamour of the starling with its shimmering coat or the cocky, colourful charm of the robin. They were just boring old sparrows.

Funny how you don't miss some things until they're gone. The plight of the sparrow has been reiterated this week in a new report by the RSPB and Exeter University. It estimates that Europe has 421 million fewer birds today than 30 years ago and that about 90 per cent of the losses have been among common species including, you guessed it, sparrows, as well as starlings, skylarks and grey partridges.

This is by no means the first report to highlight losses among garden birds. The scientists suggest the decline could be due to modern intensive farming methods and the fragmentation of habitats.

But the picture is not straightforward, since not all common birds are declining. Populations of great tits, blue tits, robins and blackbirds are all going up, Europe-wide. So why the variation? Jeremy Wilson, head of conservation at RSPB Scotland, says some migrant species may be suffering due to difficult conditions in their over-wintering grounds. Some species may also be better than others at adapting to gardens instead of wild land.

In Scotland, where the picture is probably rosier than for England because of differences in the landscape and population, starlings and swifts are the common garden species giving most cause for concern. Both may be facing a shortage of insect food, while swifts, which have halved in numbers, could be struggling to find nest sites as roof spaces where they would once have nested are blocked up. The swift may also be facing problems on migration.

The other group causing anxiety in Scotland is waders, particularly curlews and lapwings, with half of the breeding population lost since the mid 1990s.

Perhaps the most telling aspect of the new report, however, is the finding that while common birds are declining, rare species such as the marsh harrier and white stork are increasing in numbers, probably due to conservation programmes. What this means is that we are good at preventing the extinction of rare species, but much less good at protecting common species from problems caused by the way we manage the environment. It costs a lot less to increase bird numbers when the population is small to start with than when it is larger.

But unless we find ways of conserving common species, we risk beloved birds being relegated to nature reserves, warns Wilson.

He wants to see special protected areas for birds maintained and extended, but also warns that too little agricultural and forestry subsidy goes into wildlife measures. That needs to change. Meanwhile, the rest of us can help by feeding birds, putting up nest boxes and volunteering to help monitor bird populations.

Those little brown creatures need all the help they can get.