The sun is high in the sky and it already feels like midday as we walk down through the pretty village of Northiam. We pass hawthorn hedges wearing their first blossoms and cross the River Rother at a narrow bridge, admiring the boats moored below.

Our path takes us downstream along the calm valley, through fields adrift with wildflowers - pastel blue forget-me-nots, sunny dandelion flowers and fuzzy dandelion clocks, delicate pink milkmaids (a.k.a. cuckoo flowers or lady’s smock) waving on their long stems and bold yellow wild mustard flowers echoing fields of rapeseed nearby. When we stop for lunch, we add a few foraged leaves to our sandwiches: milkmaids are a kind of peppery cress and wild mustard is also edible.

Relaxing on the sunny riverbank, the day feels long and lazy, as though the hours have slowed to a halt. The call of skylarks and the whistle of the heritage steam train on the Kent & East Sussex Railway adds to the feeling that the years have been wound back. When we finally drag ourselves away from our dozing, a herd of curious steers is gazing down at us from the track above.

But within half an hour, the sky has clouded over and a chill wind is blowing up from the marshes. At Blackwall Bridge, we re-cross the Rother and join the Sussex Border Path. Maintenance of this 150 mile long distance path has recently been taken over by the Ramblers, and new waymarkers direct us over rolling fields, down hedge-lined farm lanes and through bluebell woods.

We stop in an idyllic grove beside a reed-lined pond for our afternoon tea. Sheltered from the wind, we fall asleep, lulled by the rumble of a tractor ploughing a nearby field. We wake to a splash in the pond and a quiet rustle in the reeds - my partner says he sees a water vole, but my eyes are not so keen!

The last section takes us through Beckley and back to Northiam. We hang over a hedge to watch a delightfully furry pig at Swallowtail Hill farm, negotiate a series of increasingly treacherous stiles, admire an overgrown orchard and are followed by a friendly dog.

There are a few moments of confusion - when we miss a turning, or when the way is overgrown with rapeseed - but soon enough the path deposits us back in Northiam at journey’s end.

It’s hard to imagine what the locals must have thought of Bodiam Castle when it appeared on the scene in 1385. Even now, through modern eyes accustomed to epic feats of architectural engineering, it’s a wonderful sight: the round towers rise sheer from the surrounding moat and the stone walls glow pale gold in the sun. And it’s still a surprise to come across it, nestled amid vineyards, hops farms and white-tipped oast houses, looking out across the lush pasture of the Rother valley.

The winter sun sparkles on the frost as we head east from the castle along a farm track, crunching ice beneath our boots. It’s a glorious day under a big, blue sky, and we’re not the only ones outside enjoying it.

To the north, the square tower of St Nicholas church at Sandhurst Cross hoves into view. As the river twists away to our right, we cross Kent Ditch and head uphill, leaving East Sussex behind.

We pick our way across a muddy field and through an even muddier wood. A frantic volley of gunshots erupts close by and, realising it’s a party of duck shooters, I briefly consider turning saboteur. Instead, we push on, appreciating the open views towards Sandhurst with its clock tower and windmill.

At St Nicholas, the congregation is leaving after the Sunday morning service. We sit in the churchyard for a while, drinking in both the view and a thermos of tea, trying to keep warm in the wind.

Inside the church I read about the bells, including the John Bell, which was cast in the late 15th Century, cracked in 1961, then repaired with new technology and re-hung in 2009. We also admire a window constructed of salvaged fragments of old glass and prayer cushions decorated with everything from hovercraft and Boeing jets to badgers and biblical quotes.

From Sandhurst Cross, walkers can take the road straight back to Bodiam, but we venture on to join the Sussex Border Path.

If the first half of the walk was characterised by big things - castles, skies, views, churches - then the joy of the last section lies in the details. The first crocuses are blooming, joining snowdrops and daffodils at the side of the road. We pass a well-used badger sett. Multicoloured lichen adorns a fallen tree and a bright orange jelly-like fungus emerges from a fallen branch.

After weaving our way over the hills, we slip down a narrow path beside a vineyard to emerge back at Bodiam Castle, just in time for lunch at the the National Trust tea rooms.

We tried to keep an extra keen eye out for animals and birds this month. Around East Sussex and Kent we saw (in addition to the species in our courtyard): wood pigeons, collared doves, jackdaws, crows, rooks, herons, herring gulls, black headed gulls (they look like they’ve face-planted in black ink), a buzzard, a kestrel, geese flying over, wrens (or other Little Brown Jobs), chaffinches, rabbits, foxes and deer (though these were in a deer farm). We also heard woodpeckers and found owl pellets, though we didn’t see the woodpeckers or the owls.

At the end of the month, we were in London and Norfolk. In London we saw (in addition to species mentioned above) a scruffy mouse at a tube station, then in the outer suburbs we saw nuthatches, parakeets and woodpeckers. On the way to Norfolk, we drove past two camels at a funfair, saw many rooks in rookeries, spotted a number of kestrels and a couple of buzzards. 

During our stay, we spied oystercatchers, a little egret, a skylark (or something equally noisy in flight), moorhens, ducks, house sparrows, several hares (on the last day of February, so they weren’t mad March hares yet), a bar-tailed godwit and a smaller wading bird that might have been a redshank.

This was a fun challenge. It reminded us to pay special attention to animals and spend a few extra moments trying to identify them. We were pretty happy with our species total, too - not bad for people who get most of their wildlife knowledge from Springwatch.

But during the course of the month, I started to realise just how few animals we were seeing. For example, it seems normal to us to be excited by a skylark, but this was an extremely common bird within living memory. Likewise, it would have been inconceivable to someone doing this challenge in a rural area in the 1980s to not see a hedgehog - not even a squished one on the road. So many of the animals we spotted have experienced alarming declines in population over the last ten, twenty, fifty years. Even house sparrows and starlings are now red listed in the UK .

There have been some recent success stories: buzzards and red kites have made a comeback, some birds that live well alongside humans (blue tits, robins, blackbirds) are flourishing and although we didn’t see any wild otters they are also scrabbling back from “the brink of extinction”.  But overall, there are huge declines in UK bird populations (especially farmland birds), invertebrate populations worldwide and UK wildlife in general.

Something I read this month, which made me stop and think about this issue, was a fascinating piece of community research by a local primary school and conservation volunteers. They'd published a little pamphlet outlining the history of a village water meadow. As part of the research, they’d collected oral histories from local residents, who were first-hand witnesses to the decline of wildlife in the area. One account was from a person who described how as a child they could go to the meadow and see hundreds and hundreds of frogs: now the school children were lucky if they managed to spot a handful.

This reminded me of a chapter in Collapse, where Jared Diamond talks about the deforestation of Rapa Nui (Easter Island) and its disastrous effect on the human population there. Reading that story, our inclination may be to wonder why an islander chose to cut down the last tree, what went through their mind when they did so, how they could have destroyed that final specimen of what was once a forest. But Diamond reminds us that this deforestation took generations to complete: the person who felled the last tree had never seen a forest.

Such is the case with declining wildlife populations. I think it’s one reason that going out wildlife spotting - with children, with great-grandparents, with migrants, with people from multiple generations, with city people and country people - is so important. It’s one thing to say: “Species X has declined 70% in the last 35 years.” It’s another thing to engage a child in a story: “When I was your age, I would see dozens of Species X on this walk. Why do you think we’ve only seen one pair?”

It's not just children who need this. I’ve been in the UK for over three years and I have never seen a (live) wild badger, wild otter or wild hedgehog. I've seen one slow worm and two snakes. I don’t know what else I’m missing. It’s relatively easy to notice what’s there. It’s much harder to notice the absence of something you’ve never seen.

So, go wildlife spotting! Talk about what you see. Talk about what you don't see. Talk about why that might be. Talk about what you might be able to do to help wildlife survive and, hopefully, prosper.