We're all aware of the old canary down a coalmine story. Miners would drop tools and flee if their caged canaries fell from their perch as it indicated the presence of poisonous gas.

Well, there is now a European study underway to establish if the decline of our common house sparrow, down 68 % between 1994 and 2009 (BTO Breeding Bird Survey data), is in any way linked with air pollution.

We know that a lack of food and nesting space are part of the reason, and have long suspected other factors of having an impact. Now the European Commission has published a preliminary paper on the subject. They've found that house sparrows living in highly polluted urban locations have significantly lower haemoglobin and anti-oxidant capacities, which they claim indicates the birds have been exposed to high concentrations of toxic chemicals. Haemoglobin is an important part of red blood cells. In birds and most other animals, it transports oxygen from the lungs around the body.So, do you have a gas mask in my size? Image courtesy of Mike Lawrence.

This comes as a group of UK MP's recommend schools, care homes and hospitals should not be built near main roads to avoid "tens of thousands" of premature deaths caused by what they describe as the "invisible killer" of air pollution.

The Commons Environmental Audit Committee chair, Joan Walley says officially 29,000 people a year in the UK die as a result of air pollution, but that doesn't take account of NO2 levels from diesel engines. Another independent UK Government report due out shortly estimates there is an additional 30,000 deaths a year caused by NO2 in the air. In London, Mayor Boris Johnson's official estimates put the death toll from air pollution (not including NO2) at 4,267 in 2008.

The implications of the EC report on house sparrows is that they may be a natural indicator of pollution which we've overlooked. While the findings are in line with what we know of air pollution, it's too early to say whether it's a contributory factor in the decline of house sparrows.