IT is a well-known fact that some of our formerly common birds are in serious decline.

If we were to do a straw poll in Ryedale to name names, I suspect that many people would suggest the song thrush, greenfinch, cuckoo, skylark and turtle dove maybe.

I doubt, though, the house sparrow would appear on many people's lists, because in our neck of the woods they still seem as common as ever.

Now, I’m speaking from personal experience here as a village-resident and am fully aware that people in Malton and Pickering may well disagree with me on this one, because it is in towns and cities in particular that sparrows have declined dramatically. In the City of London, for instance, the "cockney sparrer" is officially all-but extinct.

What makes the situation all the more worrying is that we still don't know exactly what is causing this population slump. As long ago as the year 2000 the Independent newspaper offered a £5,000 reward to anyone in the scientific community who could come up with a definitive explanation, and the money is still lying there unclaimed.

The current theory holding most water is that urban car diesel fumes are poisoning aphids which the sparrow chicks depend on for food in their early days. The cheerful chirruping of baby sparrows in the ivy under our house eves last spring is testimony to the fact that there is no shortage of greenfly in our garden at least.

This time of year sparrows have no chicks to feed, even if there were any insects around, so they are back to their normal diet of seeds.

Being such resourceful and adaptable characters, house sparrows are quick to take advantage of any food that we might put out in our gardens. They are definitely the top dogs of the regular visitors to our peanut feeder, bossing any blue, coal or great tit that has the temerity to try and jump the food queue.

The other day I spent a fascinating half an hour or so, gazing out through the kitchen window to try and suss out the nut pecking-order.

Coal tits, it turns out, are at the bottom of the ladder, followed by blue tits, then great tits, then female house sparrows and finally male house sparrows (unless of course our local great spotted woodpecker turns up).

It was while I was doing this mini scientific survey that I made a delightful discovery. Not only do we have lots of sparrows in our garden, we also have lots of different types of sparrow - well, three to be exact.

In among the grey-capped and white cheeked male house sparrows there was the occasional, slightly smaller and very subtly different-coloured bird, with a brown cap and a black smudge on its white cheek. This was a tree sparrow – closely related to house sparrows (Passer montanus as opposed to Passer domesticus) and genuinely uncommon.

The third sparrow is a little bit of a fraud. Hopping around surreptitiously on the floor beneath the feeder, and hoovering up leftovers, was a drab, grey-brown bird not unlike a female house sparrow. This bird goes by the name of hedge sparrow but, as it is not a true member of the sparrow family, its alternative name of dunnock is probably better used.

They may not be the most glamorous of birds but give your garden sparrows a bit of attention this month while your garden feeders are still up. I think that they're a lot more interesting than we may imagine and perhaps a little more vulnerable than we would wish.