I saw the falcon – a peregrine or a hobby? – gliding high, silhouetted against the glare of a late summer afternoon. Behind me, small birds chattered obliviously in their favoured thicket. The falcon dipped and disappeared. I wondered where it had gone, then sensed a movement where no movement should be and, suddenly, for a fraction of a second, I was face to face with a hobby at full throttle – hurtling at the unsuspecting sparrows behind me. There was a rush of disturbed air against my ear and I caught the ferocious intent in its yellow eyes and it was past me, rearing up over the shrub and diving beyond it as a dozen small birds scattered.

This didn’t take place in an RSPB reserve or on a moor. It was right in front of my house in Catford, south-east London, as I cycled back from Tesco, and was a reminder that genuinely exciting wildlife drama can happen right on your doorstep.

Hobby falcon. Photograph: David Tipling/Alamy

This is what seasoned birdwatchers and the mildly curious will be clinging on to as the nation shuts down over the coming weeks. After all, yoga on Zoom isn’t for everybody.

Some of us have always scrutinised the skies above our homes and gardens but the Covid-19 crisis has turned this activity into something of a movement, sparked by Matteo Toller of Udine in north-east Italy who recently set up #BWKM0 (birdwatching at zero km) on Twitter to help people record their sightings, share knowledge and show solidarity during the country’s lockdown. Matteo himself recorded 51 species from his windows in 12 hours earlier this month, including brambling, black stork, goshawk and the first house martins migrating north.

London’s David Lindo, AKA the Urban Birder, is currently quarantined in Spain from where he is tweeting sightings from a rooftop in Mérida and hosting live birding streams on Facebook. David’s enthusiasm is undimmed by his confinement: “The sky is a great arena, anything can fly past and, at the very least, it will give you peace. My message is simple: keep looking up,” he tells viewers on day eight of his vigil.

Some ornithologists, such as YOLOBirder on Twitter, have set up a light-hearted scoring systems to add a frisson of competition to their patient watch. His “fantasy birding in quarantine” (#FBIQ) rewards extra points for “weird behavior” and “sexy stuff”; a dunnock, for example, wins only three points on its own, but throw in a sighting of “obvious polygamy” and extra points are awarded.

Here are the rules!

1. Pick a squad-must cost less than £100m

2. Choose 11 players for the game day today-declare it before 10am

3. Watch your garden! (Start before 10am if you like 👍)

4. Players score for different behaviours etc

5. Submit score on Twitter before 9pm pic.twitter.com/W8SUx52iKc — YOLOBirder (@YoloBirder) March 23, 2020

Expert birder Steve Gale’s personal garden list in a Surrey-London suburb extends to 92 species and includes spoonbill and honey buzzards. “That’s phenomenal,” I tell him, astonished.

“It isn’t phenomenal,” he says. “It’s just that most birdwatchers don’t systematically observe birds at home. If you start learning the calls and how bird movements relate to flight lines, which use local landmarks, such as rivers and railways and habitats, you can quickly start adding to your list.”

Steve’s blog, North Downs and Beyond, based around his “uber patch” where suburbs meet farms and woods, is a treasure trove of flora and fauna observations and a virtual meeting place for likeminded people from all over the country.

He too has responded to the Covid-19 threat with a gently competitive birding challenge, inviting people to record sightings from their windows.

House sparrow in a garden near Epsom. Photograph: Steve Gale

He advises that the coming month, when many birds are on the wing for thousands of miles, is one of the best to start studying your “patch”, whether you have a garden or just a neighbouring tree and area of sky to study. This is because migration times are when birders expect to see most activity. Birds on the move can often be seen overhead and sometimes even stop by for a rest or meal in your garden or street, he says.

“We once had a black redstart turn up in late March that stayed a week in our garden. It found food and hung around for a rest. They come from North Africa or southern Europe at the end of winter.” And, within the next week or two, swallows, house martins and swifts will begin to arrive from sub-Saharan Africa; the latter will make urban skies a little noisier – and their screeching calls will be easier to hear as the whine of jets has almost vanished.

The same goes for autumn, says Steve, who is also a bird-counting specialist. “There are days when my suburban garden can be better for observing migrating thrush than famous RSPB reserves. I’ve had 4,000 redwing pass over on days when Dungeness has had barely 20.”

April is also a great time for wader passage, by night and day. Steve has heard relatively rare birds – such as bar-tailed godwit and whimbrel – passing overhead on journeys to and from the north of Scotland and the Arctic Circle. Why they’ve chosen to fly over the London suburbs as opposed to sticking to the coasts is unknown.

Bar-tailed godwit around the Thames estuary. Photograph: Dan Kitwood/Getty Images

“People are starting to buy microphones to use at night to hear calls. They are finding out a lot of new things about what flies at night … sea ducks like common scoter cuts across land we’ve now found.

“What this quarantine/suppression of movement can do is to make people realise there is so much more to see at home. But it can be difficult – sometimes nothing happens, you’ve got to be prepared for that,” says Steve.

I telephone Dave Woods, a birder who lives in one of the large Medway towns. I’m shocked when he tells me that he and his family have had mild symptoms of Covid-19 over the past week. I ask him whether he is well enough to take an interest in garden sightings (he’s built up a list of 77 species). He says: “No, absolutely not.” He pauses: “Though I did open a window yesterday for a puff of fresh air and heard my first blackcap this spring.”

Brambling (Fringilla montifringilla). Photograph: Robin Chittenden/Alamy

Among his favourite records was a brambling that decided his garden was a good place to build up strength before setting off for its summer breeding grounds in Scandinavia or Russia.

He advises observers to keep a keen watch in severe weather: “In response to storms, unexpected birds can turn up in gardens or fly over urban areas as they try to reorientate … even gannets may be seen over inland gardens after bad conditions at sea. And particularly in north-easterly winds, clusters of waxwings sometimes show up in gardens, car parks and petrol stations where they’ll eat hawthorn, cotoneaster and pyracantha berries and any fruit left on trees, particularly when berries aren’t plentiful back home in their Nordic, Russian and Baltic breeding grounds.”

My encounter with the hobby last summer may seem a moment of great luck but the sighting was typical of the wildlife drama playing out all around us all the time. As the Urban Birder said, “the sky is an arena”. And so our watch begins.