EVER SINCE I offered myself up as a volunteer birder at Sir Winston Churchill's former home at Chartwell in Kent, one question has been bugging me. Why?

I don't mean why be a birdwatcher at Chartwell, it's as good a place as any and better than many I could name. But why be a birder at all? It's not as if they are at the leading edge of fashion, even if celebrities like Sean Bean, Mick Jagger, Jeremy Clarkson and Margaret Atwood have all come out as birders. 

Non-cognates, if I can call them that, seem to regard the entire pantheon of birders as 'twitchers' who dedicate their lives - and considerable amounts of money - to tearing around the British Isles in search of 'rarities'. And the sight of anoraks (literally and metaphorically) huddled together in supermarket car parks or on sea walls with their Swarowski spotting scopes and storm kettles does little to mitigate that nerdy image.

So, to put the record straight, while it is true that all twitchers are birdwatchers, not all birdwatchers are necessarily twitchers. The RSPB has more than a million members, and 500,000 people took part in the UK's 2017 annual garden birdwatch. They can't all be chasing pied wheatears and pomarine skuas around the country every Thursday. There's an economy to support.

There are to my mind three degrees of birdwatcher: the twitchers; the ordinary or casual birders; and the ornithologists. Twitchers do, in fact, chase rarities. Quite often they also chase other twitchers who know where the rarities are. Ornithologists, properly speaking, are scientists who study avian life forms, and are quite often based in august educational establishments. Sometimes, and to introduce a layer of complexity, twitchers and ornithologists turn out to be the same people. (It would be wise, incidentally, not to throw the faintly disparaging word 'twitcher' around as casually as I have done here - especially if you don't fancy a painful encounter with a storm kettle.)

Ordinary birders may not be as knowledgeable as the twitchers and ornithologists but they can nevertheless identify several, perhaps even many, different bird species. The range of knowledge among the ordinaries is wide. There will be casual birders who can, at a glance (or, more likely, at a listen), tell a chiffchaff from a willow warbler, and there will be those who do not yet understand that black-headed gulls do not always (if ever) have black heads, that common gulls aren't that common or that pheasants are not British birds, despite the vast number that end up as roadkill in Britain every year.

And that difference in the level of knowledge is okay, isn't it? The point is that all of these hundreds of thousands of humans have an interest in birdlife, and all degrees of birdwatchers should applaud that. In any event, by pursuing the interest the bad birders* are certain to get better. 

My career as an ordinary birder is prosaic. I was introduced to the joys of birdwatching (only a few years before I discovered that girls were quite interesting too) by a schoolfriend whose enthusiastic and learned older brother worked for the Forestry Commission. Peter is no longer with us, but I still treasure his passion for birding as well as the beautiful drawings he would make in his field notes. (The scrappy one below was dashed off by me, for purposes of illustration, and is woefully inferior, like a tribute band playing slightly off key).

The thing is that once you can tell a jackdaw from a carrion crow or recognise a woodpecker's bouncing flight pattern, you simply can't not know and see those things, even if you are walking hand in hand through scented meadows with the girl of your dreams on a summer's day full of sensual promise. It's like asking a car dealer on a date not to know the difference between a Lamborghini and a Golf.

Once a birder, always a birder then. And so it has turned out. I have always owned binoculars. I have always had a field guide somewhere in the house or car. And I have always spotted birds, wherever I was.

There were always birds to spot too, often in the most unlikely places - like the stunning peregrine falcon I first heard and then saw above Berkeley Square in Mayfair (where nightingales have almost certainly never sung, incidentally).

The sheer joy of seeing the fastest creature on the planet above the ancient plane trees and exclusive boutiques lifted a day full of pedestrian business meetings from deadly dull to simply fantastic. That's what birding can do for a chap.

The emotional response may, in fact, be atavistic. We humans are an intuitive and pattern-seeking species. We evolved that way because it gave us an evolutionary advantage: that ability to turn bits of data - it's fast, it's furry, it has long, curvy teeth and it's heading this way - into data sets that spurred us into action (get the hell out of there), was life preserving.

These days we still collapse data into sets, which allows us to make automatic, rapid and sometimes inaccurate judgements all of the time - that's why we all know what we think about estate agents, journalists, politicians, immigrants, American presidents and twitchers, even if what we think we know is unlikely to be universally true on closer inspection. It's also why we see faces and animals in the flames from a fire or in clouds, and images of religious icons in bits of burned toast: we are genetically engineered to look for things we recognise, for good or ill.

That evolutionary habit of looking for patterns in data finds a real focus in birding. Knowing the characteristics of a bird - its data set, or jizz - leads to an identification that produces a resolution as satisfying as the shift from a seventh to a major in music. (It's not just birding, of course, football supporters, jazz aficionados and coin collectors have their own ways of finding pattern resolution too.)

Whatever the reason birding is popular, it's a good thing. Birds need our help. As the British Trust for Ornithology (BTO) said in its latest research The State of UK Birds 2017: "Volunteers play a crucial role in monitoring the UK's bird life."

Climate change is changing everything. To quote the BTO report again:  "Birds in the UK are showing changes in abundance and distribution, predominantly moving northwards, in a way that is consistent with a changing climate."

The quietly-beautiful starling is now red-listed as being of "greatest conservation concern". So too is the house sparrow. This doesn't necessarily mean that populations are sparse, which is why you still see these birds. It means populations are declining, and at a rate that is worrying.

The picture is not universally bleak - blackcaps are doing well in the UK, for instance, and egrets, we've had a few** - but without twitchers, ornithologists and ordinary birders helping keep track of what's going on, we won't know precisely which species are under threat. And we could lose some of our most beloved birds, just like that. It's already happening.

Which kind of answers the question posed in the intro - why be a birder? Because - and to coin a phrase - every little helps.

• I slightly borrowed the term 'bad birder' from Simon Barnes's excellent introduction to the pursuit: How to Be a Bad Birdwatcher. Highly recommended.

** I didn't slightly borrow the line about egrets - I stole it from the Medway newspaper it appeared in some years back, if only to prove that not all local newspaper headlines are ephemera. And to the sub-editor who came up with it, I doff my hat.

Everybody can identify a robin. So, in a small way, everybody is a birder.  © Erik Brown 2018

Everybody can identify a robin. So, in a small way, everybody is a birder. © Erik Brown 2018