The eyes have it. At least they do when it comes to spotting small nocturnal mammals in dark treetops. And the two eyes that suddenly materialise in our torch beam stop us in our tracks: twin points of disembodied light fixed in the blackness, like candles in a cave. We crane up through the foliage for a better view. Then just as suddenly – as though switched off at the wall – they disappear, leaving our beam to play aimlessly over a bare branch.
"Quick!" urges my guide, Nilantha, pointing with unerring certainty to the right. "That tree there." And sure enough, we're soon on to those eyes again – this time for long enough to clock their owner. Bingo! It's a slender loris. This diminutive, bizarre-looking primate is found nowhere on the planet but Sri Lanka. Binoculars reveal saucer eyes and skinny limbs as, looking like some arboreal ET, it scrambles away through the branches.
It is one of those wildlife eureka moments: one second you're trudging along fruitlessly, your mind set on dinner; the next, you're eyeballing something straight out of an Attenborough documentary. Granted, a slender loris is hardly big game. Nonetheless, there's a thrilling sense of secrecy to the sighting and I'm delighted my last night has produced something so special. Walking back, the orchestra of frogs and crickets seems to shift up a gear and the fireflies twinkle that much more vigorously.
Rewind a week or so and I'm watching and waiting for another unseen animal. This time the setting is a dusty 4x4 in the midday heat of Yala National Park, far to the south-east, and the animal is rather larger than a loris. The alarm whistles of spotted deer have given the game away and now, as agitated monkeys join the chorus, there's a tension in the air that can only mean a predator at large. We don't wait long. Out on to the sandy road pads the spotted feline form we'd been hoping for. "It's a young male," says my guide, Chitral Jayatilake, leopard photographer extraordinaire. "I recognise this chap; his mother must be around somewhere."
The leopard pauses, fixing us with a amber-eyed glare and twitching the curled tip of his long tail, then slinks into the thorn thickets. Freewheeling gently forward, we watch the dappled shoulders seesaw through the long grass to the foot of a tamarind tree. The cat peers around again then in one fluid bound is up aloft, draping himself over a branch as he settles down in the shade of the canopy.
Wildlife sightings don't come more impressive than a close encounter with a leopard. And leopard encounters, it seems, don't come any easier than at Yala where, with no larger predators for competition, this notoriously elusive cat has grown unusually bold. My four days in Sri Lanka's premier national park produce five excellent sightings: a success rate that competes with anywhere in Africa.
But Yala is not only about leopards, despite the one-track agenda of many visitors. Wildlife here is prolific. At ancient man-made reservoirs, known as tanks, we watch water buffalo wallow in the shallows, while shy sambar deer tiptoe down to drink and wild boar root beneath the fringing trees.
On a quiet loop road, large tracks lead us around a corner to a party of elephants. The beasts crash away into the bush, trumpeting their displeasure and shepherding a young calf to safety, its fuzzy contours just visible between the legs of its elders. The birds are impressive, too. Some seem strangely familiar: the peacocks that strut around the clearings and the junglefowl that dash through the thickets are perhaps too reminiscent of their domesticated descendants to earn the admiration they deserve. But others, such as the huge-conked Malabar pied hornbills that lurch overhead and the little green bee-eaters that hunt hawk dragonflies beside the road, are captivating.
On our final day, bouncing back to make the park exit before sunset, we jam on the brakes as a shaggy black mop ambles into a roadside clearing. It's a sloth bear, lured out by the scent of fruiting palu trees on the evening breeze. The animal raises a long pale muzzle to sniff myopically in our direction before shuffling back the way it came.
Back at the lodge that evening, as another 4x4 swings into camp and disgorges its cargo of khaki-clad visitors, I find myself mystified that Yala is so little known. But Chitral reminds me that this jewel of a park – like most of Sri Lanka – has had more than its fair share of troubles.
First there was the tsunami. Yala sits beside the Indian Ocean, and both staff and guests at the reserve were among the thousands who lost their lives on the morning of 26 December 2004. Our driver, Ajith, describes how he had turned inland on impulse to follow up a rumoured leopard sighting and missed by minutes the fate that befell four tourists at a beachfront picnic site. He shows us the memorial that now commemorates this tragedy, but even now he will not set foot on the beach. "Perhaps one day," he says. "Not yet."
And then there was the war. In May 2009, the Sri Lankan government finally brought a bitter end to the civil conflict that had beset the island for more than 30 years. In its later stages, the LTTE (Tamil Tigers) had established camps inside Yala, prompting the authorities to close all but one sector of the park, in effect bringing tourism to a standstill.
Today, controversy rages over the brutal resolution of the conflict, and thousands of people in the north remain displaced. Yet there is an overwhelming sense that the island is again opening up. And the good news for the visitor seeking wildlife is that neither war nor tsunami seem to have had any lasting impact on the natural environment. Indeed, while Yala is Sri Lanka's top safari drawcard, Chitral tells me how other long-neglected national parks, such as Wilpattu in the north-west, are teeming with wildlife and ripe for exploration.
No visitor to Sri Lanka can ignore the island's rich cultural heritage. And so from Yala we head northwest towards Kandy, the sacred Buddhist city that was the last of Sri Lanka's ancient Sinhalese capitals before the British took over in 1815. On the map it looks a shortish journey. On the road, however, we spend the best part of a day toiling up from the paddyfield patchwork quilt of the south-west, via the hairpins and waterfalls of the escarpment, on to the central plateau, with its topiaried tea estates and colonial hill stations.
At each stop along our route nature and culture are pleasingly intertwined. Thus the great granite Buddhas at Buduruwagala are set off by a crested serpent eagle that circles above them, while woolly furred bear monkeys – a mountain race of the endemic purple-faced leaf monkey – cavort around the treetops of Hakgala Botanical Gardens, where quinine was developed.
This same alluring blend continues the next day as we head east from Kandy to explore the ruins of Anuradhapura, built in 400BC as the first of Sri Lanka's ancient capitals. Despite the sheer scale of this site – one enormous stupa comprises 90 million bricks – the experience is overwhelmingly relaxing. Barbets call metronomically from the fig trees that shade our wanderings and grey langur monkeys strut around temple walls like delinquents on a school trip. In one rocky outcrop we enter a cave to find an orange-robed monk meditating on a rush mat, as though the last 2,000 years had never happened.
More World Heritage Sites follow, including the monumental rock fortress of Sigiriya and the overgrown ruins of Polonnaruwa, the island's second ancient capital. And as I brush up on my Buddhist mythology and marvel at the technology of ancient reservoir sluices, so my wildlife count ticks over: golden jackals trotting across the road; a roost of flying foxes; a two-metre-long monitor lizard.
The theme continues back at the delightful Chaaya Village hotel in Habarana, my base for exploring Sri Lanka's "cultural triangle". Here I discover giant squirrels and brown fish owls in the lakeside trees, and watch a mongoose scamper across the restaurant terrace as I tuck into yet another fabulous curry.
A short drive from Habarana is Minneriya National Park, notable for "The Gathering" – a seasonal congregation of elephants that is perhaps the largest in Asia. Numbers peak at more than 300 in July and August when the lake is at its lowest. At the time of my visit they were more widely dispersed, but we still find good numbers browsing the tall grasses of a nearby "ecopark" and even meet one impressive tusker sauntering down the main road as we return to the lodge after dark. Sri Lanka's jumbos, it seems, know no boundaries.
The challenge this presents to farmers is vividly brought home the next morning on a guided nature walk through the community around Habarana. Rickety wooden watchtowers among the paddyfields overlook the tangled forest edge, from where crop-raiding elephants emerge soon after dark. I ask one watchman, via the translation of my guide, TK, how he deters the raiders.
"I shout as loud as I can," he explains, and nods towards his assistant – a ferocious-looking dog chained to a coconut palm. But I'm guessing that the job might be a little trickier than he is letting on.
Marauding pachyderms notwithstanding, one could easily become dewy-eyed about this place. The homesteads, while basic, seem well-provided, the fields are fertile and well-irrigated, and nature runs riot in a manner that would surely be deemed unproductive by most Western farmers. We stroll between homesteads, watching chillies being harvested and sipping fresh coconut milk. Meanwhile, TK keeps up his nature guide's vigilance, spotting an emerald vine snake camouflaged among the foliage, a crocodile slipway at the water's edge, VC and an exquisite sunbird nest – fashioned from spider webs and lichen – in which we can just see the protruding bill of the sitting female.
We return across a reservoir by dugout canoe, kingfishers flashing past the bow, and then transfer to a bullock cart for the final stretch. Lying back on the boards I close my eyes and listen to the creak of wood and leather and the soft commands of the driver, as we rumble over the ruts and puddles left by last night's elephants. Our morning has hardly been a big-game safari. But for sheer immersion in nature – and a culture with which it seems seamlessly integrated – it has been every bit as satisfying as chasing leopards around Yala.
Sri Lanka's final wildlife secret is a big one – literally. Recent years have revealed a large and hitherto unknown population of blue whales off the southern coast. In peak season, from November to April, the port of Mirissa records sightings on more than 90 per cent of boat trips: a success rate that compares with any on the planet.
My arrival in Sri Lanka has coincided with the start of the monsoon, which means the southern seas are too rough to risk a tourist. With the war over, however, a new whale-watching front is opening up in the north-eastern port of Trincomalee, where weather patterns are different and the whales often venture close inshore.
Chitral's mind-blowing photographs are too hard to resist: we decide to take the road north and give it a shot. Soldiers wave us through military checkpoints with a smile. And "Trinco", when we arrive, seems to be thriving: my swanky hotel, the Chaaya Blue, opened just days earlier.
Unfortunately the whales play hard to get. After a morning fruitlessly combing the horizon for spouts and tail flukes, we admit defeat. A shake of the head from passing Tamil fishermen confirms that there've seen none this week.
Fair enough: if I'd wanted my whales served on a plate I should have turned up in the south a month earlier. All the more reason to return to Sri Lanka, I reflect, as our boat turns for home. And besides, where's the fun in wildlife if it just follows the itinerary?
As if on cue, three sleek backs break the water across our bows. "Spinner dolphins!" shouts Nilantha. "Look to the left." I turn to see the water churning for 100 metres or more as a flotilla of these exuberant cetaceans bear down on us.
There's nothing like a dolphin or two for raising the spirits – let alone 200 of them – and their beaky grins seem like a fitting final image with which to leave Sri Lanka. But I still have one more night left. "Now Nilantha," I say, "about that slender loris..."
Travel essentials: Sri Lanka
* Mike Unwin was a guest of World Big Cat Safaris (01273 691 642; worldbigcatsafaris.com) and the Sri Lanka Tourist Board (0845 880 6333; srilanka.travel). A similar tailor-made 14-night trip from World Big Cat Safaris costs from £1,950 (per person based on two sharing), including internal transfers, half-board accommodation, game drives in Yala National Park, a whale-watching expedition and a variety of cultural and historic excursions. International flights to Colombo are not included.
* The only non-stop flights from the UK are on SriLankan (020-8538 2001; srilankan.aero) from Heathrow to Colombo. Connecting flights are widely available on Gulf-based airlines: Emirates, Etihad, Gulf Air and Qatar fly via their respective hubs.
* Chaaya Village, Habarana (00 94 6 6227 0047); Chaaya Blue, Trincomalee (00 94 2 6222 2307). For more information on both, see www.chaayahotels.com