From 1911 to 1986 coalminers relied on canaries to warn them of dangerous gases. The birds were taken down the pits in cages and if they showed signs of distress, the men knew they must get out quickly. Canaries react to very small quantities of deadly carbon monoxide. They were made redundant when cheaper and more reliable electronic gas detectors were introduced. The miners missed the canaries, which were treated as pets

In a way, our wild birds fulfil the same function as those canaries, because their behaviour can warn us of changes in the environment. Rachel Carson wrote her book ‘The Silent Spring’, published in 1962, to warn about the damage caused by the indiscriminate use of agricultural pesticides. If all the birds were poisoned, what would that mean for us? Not just a silent spring, but serious damage to human health. Although there are much tighter controls on pesticides now, we still rely on birds to warn us of danger, though now it’s more to do with global warming and loss of habitat.

I buy bird food by the sack, which partly explains why my garden is full of birds, including lots of sparrows. Many people think that sparrows are common, but their numbers are declining. Wherever birds have trouble finding food, they fail to breed. Last year hardly any sea bird chicks were hatched around the Shetland and Orkney Islands because there were no sand eels for them to feed on. It’s thought that the small fish are being affected by climate change and shifting currents, which are also affecting the melting ice caps.

Next weekend many people will participate in the RSPB’s Big Garden Birdwatch, which involves choosing one hour over the weekend to watch the birds in your garden or local park, and note the most you see at any one time of the several species listed in the survey. Details are in the Radio Times, or you can get a survey form from the RSPB. The results will be published in March, and will tell us whether the number of birds has increased or decreased.

One evening last week I was leaving a house in Ipswich at dusk, when a blackbird was singing nearby. I didn’t start the car straight away, but sat with the window wound down until I got cold, listening to the beautiful song. We’d all be the poorer without birds, and not just because we pick up important signals about the state of the environment from them.