It's gone midnight and an eerie half-light backdrops the hulking outline of the Broch of Mousa, an Iron Age tower. Eyes adjust to bird shapes darting all around us. One briefly brushes my leg before disappearing into the stone recess of its broch burrow. The storm petrels' relentless churring – beckoning their mates back from a feeding foray – pulses from the ancient stone walls.
This boat trip runs at dusk, to the tiny island of Mousa, a mile or so off the east coast of Mainland, the main island of Shetland. It's one of the highlights of the simmer dim – the twilight hours that linger here at 60 degrees north at this time of year. Yesterday, the longest of the year, saw sunrise at 3.39am and sunset at 10.34pm. While the sun only dips briefly for a few hours below the western horizon, twilight remains.
My trip begins at Sandsayre Pier. A birthday party from nearby Bigton arrives, bantering in Shetland dialect. Tourists and camouflaged twitchers fiddle with binoculars before the crew ushers all 50-odd of us onboard. It's a 15-minute crossing to the small isle, just 1.5 miles long and around one mile at its widest. Uninhabited since the 19th century, Mousa is now an RSPB reserve harbouring significant bird populations including fulmar, shag, ringed plover, Arctic tern, black guillemot, Arctic and great skua.
From the jetty, groups set out towards Britain's finest surviving broch. At 43ft high and 49ft in diameter at the base, the 2,000-year-old, lichen encrusted Broch of Mousa has real cliff-top presence. Entering through the low doorway its thick walls and intramural spiral staircase attest to the skill of its construction. Mousa is cited as a defensive stronghold and lovers' hideout in the Orkneyinga saga, written around 1230. Norse and subsequent settlers made alterations but it's stood sturdy while some 120 brochs across Shetland diminished, including Mousa's sister fort over the Sound at Burraland. Guided by torchlight we climb the craggy stairs to the summit walkway.
Storm petrels (known as alamooties in Shetland) return from feeding at sea, circling bat-like in the demi-night to evade predators. Helen Moncrieff of RSPB describes how these smallest of seabirds pair up for life: sharing epic migrations, foraging and egg-warming duties. Come September, they will begin to fly south to the fertile waters off South Africa and Namibia. Mousa is home to around 11,800 breeding pairs: 40 per cent of the UK population. With ears close to a stone burrow we listen. It's a sound reminiscent of skin friction across a balloon's surface, or as naturalist Bobby Tulloch described, like "a fairy being sick". Rivalling the storm petrel for weird noise is the "drumming" or "bleating" snipe: its tail-feather-vibrating ditty reminds me of a sci-fi sound-effect cue.
The Bigton crowd pops open some bubbly and we wash down some birthday cake while watching the midnight show. From the broch, a torch-lit procession of small groups tiptoes over rock and bog back to the boat. Light beams and knees wobble along the route. An ethereal glow illuminates lunar flagstones.
This is my second Mousa dusk venture, having spent the previous night experimenting with parabolic reflectors and contact microphones with leading soundman Chris Watson and some fellow budding sound recordists. On the crossing, Chris lowers a hydrophone fathoms-deep and we listen to pistol shrimps through headphones: this snapping, percussive sound made by asymmetrical claws can be heard across our oceans. He explains why Shetland is a precious place in our modern noise-polluted world – for its isolation, wildlife and sounds. Detached from their environments many of the recordings we collect, during the Natural Sound Course (part of the Shetland Nature Festival and Year of Natural Scotland), take on otherworldly guises. At one of the archipelago's few woodlands at Kergord we record rooks, a burn, stridulating ants, a dawn chorus and resolute timbers.
Chris presents the collected sounds in a 40-minute surround-sound piece in the auditorium of Lerwick's new arts centre, Mareel. This inspiring project is one of many creative events and performances. May's Folk Festival is always a blast and the Screenplay film festival, curated by critics Mark Kermode and Linda Ruth Williams, brings moving images to boats, bus stops and other quirky venues in early September. A strong sense of history, and a flourishing school music and craft tradition creates a thriving cultural scene. At Hay's Dock, facing Mareel, is the Shetland Museum and Archives brimming with maritime, social and ancient artefacts. An old mill in the verdant Weisdale valley houses Bonhoga Gallery's ever-changing contemporary arts and crafts exhibitions.
While staying at Hayhoull B&B in Bigton, the door – like most in Shetland – is left open. Natives and settlers from Montana, Guyana and Aberdeen pick up pots and keys for the summer regatta at the natural golden causeway to St Ninian's Isle. Beach clean-ups, including the islands-wide Da Voar Redd Up (spring clean) have earned Keep Scotland Beautiful awards. A strong sense of community, interdependence and mucking-in is central to island life. Surveys often cite Shetland as Britain's happiest place.
Word has got around today that a BBC film crew is recceing locations for a full TV detective series, called Shetland, based on Ann Cleeves' novels. Two of the crew meet 83-year-old crofter James Robert and mention feeling cold on this sunny June day. Robert's gentle wisdom is distilled into a few words: "You must be spending too much time in the house."
Amiable crofter and tour guide James Tait shows me around south Mainland one morning. After watching seals and pups playing in turquoise waters and hauling out on Rerwick Beach, we climb a twisting road up to Mossy Hill. James explains how on this former common grazing land, seasonal events such as driving the sheep and plucking wool would bind communities together.
Concrete and rusting relics of the RAF/Nato Ace High base are strewn around the summit below telecommunications masts. Today's pristine azure skies allow views of the fair sands of Spiggie and St Ninian's, and a horizon profile of Britain's most remote permanently inhabited island, Foula. Near the airport, at the Jarlshof archaeological site, we walk over 4,000 years of history. Among the buildings dating from 2,500BC to the 17th century are Bronze Age homes, Pictish wheelhouses, a broch, a Norse longhouse, a medieval village and a laird's manor. Those other indomitable long-maned natives, Shetland ponies graze nearby.
At Sumburgh Head Lighthouse and RSPB reserve, sheer crags are home to puffins. Storms and food scarcity (the phytoplankton and sand eel are in decline) have struck blows to seabird populations of late, and we only spot a few breeding pairs. Heading north the peat-fired warmth and ingenuity of a 19th-century home at the thatched Croft House Museum is a lesson in resourcefulness. All the rooms – bedroom (ben end) with box beds, kitchen (the butt), barn, byre and kiln (for drying corn) – are linked together by a passageway called da trance. Talk of a traditional dish of gree (liver oil) poured over potatoes and boiled fish sounds intriguing – but I have to make do with the prospect of Shetland salmon smoked by one of the few whalers still living, Geordie Robertson.
On another morning I head north with Joe Kay, one of Shetland's talented amateur photographers and birders. With camera kit, waterproofs, binoculars and the latest news on wildlife sightings, we drive to Northmavine. On the way we stop frequently to watch and listen beside voe, loch and moor, catching sight of birdlife, seals and an Arctic hare. At one point, a whistling crofter, two sheepdogs and 30-odd sheep tumble down a hill.
One of the joys of exploring Shetland is being lured by a shoreline scene and stopping to beachcomb. Amid the volcanic sand and kelp of Stenness Beach we find a salt-eroded rubber ball, sea urchin endoskeletons and goonieman's candle (birch bark ringlet carried on the tides from Norway). Incongruous white sports socks hang on the lintel of a roofless stone bod (a shelter once used by the haaf fishermen) piled with flaking-paint boat wood, rope and buoys. Later at the wonderful Tangwick Haa Museum we see labelled beach finds, whale eardrums, nautical instruments and curios from the near and distant past.
At the furthest north-western tip of Mainland is the 350- to 400-million-year-old volcano Eshaness – all contorted magma and pyroclastic debris – and a defiant lighthouse. In relatively docile weather we look over the cliff edge at sea-stack drongs, geos (narrow inlets) and blowholes battered by the Atlantic. Contemplating the giant natural arch of the Dore Holm islet and listening to the waves, it's easy to imagine this primeval terrain inspiring Norse mythology. For a more scientific narrative, Allen Fraser of Shetland Geotours reveals the layers of Eshaness' geological history on themed excursions.
After a day's adventure, we refuel on Shetland's natural larder: peerie (small) haddock, juicy blueshell mussels and chips at Frankie's, Britain's most northerly chippy in oil-boom-built Brae. And as we drive south another spectacular sunset melts into the Atlantic, its embers rekindling the day to come.
Flybe (0871 700 2000; flybe.com) flies to Sumburgh from Aberdeen, Glasgow, Edinburgh, Inverness and Kirkwall. NorthLink Ferries (0845 600 0449; northlinkferries.co.uk) sails from Aberdeen and Kirkwall to Lerwick.
Staying and seeing there
Hayhoull B&B (01950 422206; bedandbreakfastshetland.com) has doubles from £60.
Frankies (01806 522 700; frankiesfishandchips.com).
Shetland Nature Festival takes place 29 June-7 July (shetlandamenity.org).