After noting the few birds in my own garden for last weekend's Birdwatch I'd developed an itch for something more adventurous, so the opportunity to scratch that itch was like finding a scrunched-up ten pound note in a coat pocket.

Courtesy of the Gardening Leave charity, I joined a group of Chelsea Pensioners and forces veterans in the very large grounds of the Royal Hospital Chelsea; an oasis of calm and green in the chaos and concrete of central London.

Carefully crafted nestboxes We split into four groups, one to the allotments, one around the feeders (lucky bunch got to stay in the heated garden shed equipped with kettle, tea and biscuits!). A third team set-off to more open spaces and I was escorted by Col (only his Mum calls him Colin) and Joanna Wise from Gardening Leave. We didn't get the warm shed, but we certainly hadn't drwan the short-straw as we spotted the greatest variety of birds. 

Before we'd started, there was an opportunity to inspect some sturdy nest boxes made and decorated by In-Pensioners of the Royal Hospital Chelsea. The boxes will be installed by tree-surgeons around the grounds in the near future. It was as we left their greenhouse workshop that we saw a grey heron overhead, being chased away by a crow. The spectacle reminded Joanna to tell me about a woodpecker we'd probably see on our walk past a line of London Plane trees.

First on the recording sheet was a pair of magpies as we strolled towards Ranelagh Gardens. Col admitted to previously being indifferent to nature and wildlife. Born in London, he'd drifted into other interests but realised it was time to move on or be sucked into a life that would destroy him. He escaped north, joined-up and ended up being a southerner in a northern regiment. After seeing action abroad he's re-entering civilian life and exploring new options which connect him with the natural world, He's already almost single-handedly created a new vegetable garden on an old bramble patch within the hospital grounds. It's a journey he should be proud of.

Ian (left) and Col, keeping track of sightings.

Half way round we were joined by another veteran, Ian, who now works for Gardening Leave. Both he and Col admitted it was harder to spot birds than it had been to spot danger during their time in the forces. I know which challenge I'd rather accept. Birds are equipped to survive a hostile world, but they're not out to cause harm.

There were the usual suspects for west London. Crows aplenty, pigeons, robins, a solitary house sparrow (poor lonely thing). A variety of tits and some blackbirds. A formation of ring necked-parakeets screeched between the trees and then there was one sighting which kept us guessing for a while. After much head scratching and trawling through books we agreed the tiny birds we'd strained to see close-up were young goldcrests. We walked back past the row of plane trees hoping to crown our birdwatch with a confirmed sighting of the woodpecker. We'd almost given up when the squat wings of a bird in flight raised hopes. It landed high-up and vanished from view. Our hour was over and the warm shed and a mug of tea awaited.

Once everyone's Big Garden Birdwatch sightings have been reported from across the UK, we'll start working out tables of results and aim to report back in March. Meanwhile, there's still plenty to see. Robins are rearing young on their nests and London's warm climate continues to attract unusual and unexpected wildlife. We've got bearded tits in Hyde Park, muntjac deer in central London, hedgehogs roaming our parks and seals swimming in the Thames. Then there are the unexpected encounters, Like Londoner Andrea Boatswain's southbank encounter with a tame barn owl near Blackfriars bridge. You never know what you'll come across.

Andrea and barn owl at Blackfriars Bridge on the Southbank