That cheeky chappie of British cities, the House Sparrow is under threat. This much we knew. Numbers have been declining for some years, although the population around us having fallen some years back is now quite healthy again. But scientists are still trying to work out the cause of the decline.

Following up on this, and some recent research, there was an article in the Autumn 2012 issue of BBC Wildlife magazine. The article doesn’t appear to be online, so I bring you a few salient extracts.

The cockney ‘sparrer’ is falling quiet in our cities — and one problem may be too much noise.
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a small, but significant, difference in the chances of their chicks fledging — 21 percent tor those in a noisy area, but 25 per cent for those elsewhere.
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[Research suggests] noise interferes with communication between the patent birds and their offspring, which as a result are fed less often.
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a shortage of invertebrate food in the sparrows’ diet limits nestlings’ chances of survival.
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chicks raised in areas with high nitrogen dioxide levels — ie. close to busy roads — fledge at lower weights.
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Despite its position on Britain’s Red List of threatened species, the house sparrow is not rare — though it has declined, there are about 6 million pairs in the UK.
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Sparrows connect city-dwellers with nature
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the downturn has been rapid. Over 15 years between 1983 and 1998 … sparrow numbers dropped by 90 per cent in one Edinburgh park.
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the drive to renovate buildings and tidy up parks is more significant, depriving urban sparrows of places to nest, feed and take cover. Sparrows and other birds like bits of green space, evergreen cover, bushes … But we have lost a lot of scrub from parks in recent decades.
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house sparrows are more likely to thrive in areas of high social deprivation, either because buildings are in poor repair or because gardens are less manicured, improving invertebrate and seed productivity
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lead-free petrol has even been cited, with the additive MTBE being blamed for killing insects. Cats ate significant predators of house sparrows. Rising numbers of feral pigeons could be transmitting increasing levels of disease.

I don’t agree that domestic cats are the problem everyone makes out. Yes they do kill birds — so do sparrowhawks, kestrels, magpies and crows — but in my experience not that many. And in any event they are generally taking the weaker (who may have perished anyway), thus allowing the stronger a better chance of survival.

But the real lesson for me from this is that basically we don’t know. Or perhaps more accurately, there is no one factor for the decline, but many interrelated factors.

Our sparrows have bounced back despite a decrease in the number of easily accessed roofs in which to nest. But it is noticeable that they inhabit a small cluster of gardens, including ours, with a higher than normal number of bushes, hedges and trees. So the point about cover is well made. They like bird feeders too as they provide easy food, when the Greenfinches and Parakeets can be elbowed aside.

I like sparrows. There are days when you open our front door and all you can hear is three dozen sparrows all going cheep, cheep, cheep! Our front garden hedge is their local village pub. And that’s good.