Will Miles traces an evocative path through the seasons on Mousa, a nature reserve and bird lovers' paradise in Shetland.
Mousa is an uninhabited island of just 180 hectares, located about 1km east of south mainland Shetland at exactly 60° north. Looking down at the island from a low flying, ten-seater plane in February I am struck by two things. Firstly, that winter is perhaps not the best season for inter-island flying in Shetland (a series of high-speed, freezing squalls has made this particular journey, from Fair Isle to Tingwall, pretty lively). Secondly, that the shape of Mousa is of two isles joined together, with the north isle about a third the size of the south, and the outline of both drawing the eye through an intricate figure of eight.
The landscape is gentle: rolling but never very high, predominantly herb-rich maritime grassland, here and there criss-crossed by dry stone walls. Two tidal lagoons sweep deep into the southeast corner and there are two freshwater lochans, one each in the north and south. In summer the lagoons are alive with terns and waders, but from the shaking, bumping plane a few winter Eider Ducks and Herring Gulls are all that I can see, plus a wallowing, lone Grey Seal. The island looks exceptionally cold and windy, its colours are muted by dark clouds and dampness and its surfaces pummelled by hail, and suddenly I fully appreciate why its abundant bird life is now mostly further south.
Mousa has been an RSPB (Royal Society for the Protection of Birds) island nature reserve since 2000 and is managed via agreements with its agricultural tenants and the landowner, The Sumburgh Company. It is a Site of Special Scientific Interest (SSSI), a Special Area of Conservation (SAC), and a Special Protection Area (SPA) within the European Natura 2000 nature reserves network.
Right in the middle of the island, on the south isle, the largest hill rises to just 55m above sea level, encircled by the visitor path. This leads to a rare feature which for most human visitors, if not one or two other species, stands as an instinctive homing point and the focal centre of the island. It is the Broch of Mousa, an Iron Age dry stone roundhouse of spectacular height (13.3m).
The broch is exceptionally well preserved and one of just a handful of such ancient towers still standing in Scotland. Apart from a small doorway, there are no large openings in its near-vertical outer surface, just small cracks and cavities between the building stones. These little spaces are occupied by a throng of nesting Storm Petrels plus one or two pairs of Black Guillemots through the warmer seasons; however in winter, these birds are elsewhere and the tower is relatively lifeless, standing on the island’s western shore like a frozen sentinel gazing across to the Shetland mainland opposite.
For those interested in wildlife, luckily, a look across Mousa Sound in winter does not always seem so futile. Viewed from the mainland, the sheltered water usually holds a large flock of Eiders, which in several years has contained up to two, very rare, King Eiders. Also, Long-tailed Ducks, Little Auks, Black Guillemots and Great Northern Divers can be seen here, as well as regular Otters, Seals, Harbour Porpoises and, occasionally, the odd pod of Killer Whales.
Mousa can only be accessed by boat and Mousa Sound acts as the island’s natural gatekeeper. In winter the Sound is too rough for commercial boat trips to cross safely.However in April, as the Shetland spring gathers momentum and sea conditions ease, The Mousa Boat service starts up again and day- and night-trips to the island can begin.
Full springtime in Shetland can take an age to arrive, but once it has the intensity of life and colour is exhilarating. From the end of March to early June the island is refreshed by growth and change. The bird life always builds up gradually, but the plants can seem to switch from drab brown to vibrant greens, pinks, violets, turquoise, powder blues and yellows in just a few days.
Most numerous among the breeding birds in spring are the seabirds. Late March and the first week or so of April see the return of breeding Puffins, Black Guillemots, Shags, Great and Lesser Black-backed Gulls, Herring Gulls and Fulmars. Through April, Great and Arctic Skuas, Kittiwakes, Arctic Terns and Red-throated Divers reappear. Then later, mostly in May and early June, the Storm Petrels arrive. Gannet, Razorbill and Common Guillemot activity picks up through April too, although these species don’t breed on the island and many of the individuals seen passing and fishing close by are presumably breeders from elsewhere, perhaps Noss, Sumburgh or Fair Isle. Other breeding birds include Oystercatcher, Curlew, Lapwing, Ringed Plover, Redshank, Snipe, Eider, Greylag Goose, Rock Dove, Raven, Hooded Crow, Wheatear, Rock Pipit, Meadow Pipit, Twite, Skylark and the Shetland subspecies’ of Starling and Wren. On a fine day in May it is possible to see and hear all these species well, except for the Storm Petrels, within an hour of stepping off the boat.
One important reason why all these birds successfully breed on Mousa, most notably the petrels, is that the island is entirely free of rodents and cats, as well as ferrets and stoats (common on mainland Shetland). This is indeed remarkable, considering the island’s extensive history of human habitation and boat landings. During the eighteenth and nineteenth centuries Mousa was relatively well populated by at least eleven families, as evidenced by the remains of crofthouse walls and outhouses. The broch is thought to date from around 100 BC and earlier occupation is indicated by the remains of Bronze Age burnt mounds and a Neolithic homestead. Certain islands in Shetland seem to have an incredible resilience to colonisation by rats, for example Fair Isle, with its long history of boat traffic and large shipwrecks, and Uyea in the far north. It is said that the soil of Uyea has a property that deters rats and that crofters on neighbouring Unst used to cross to the island, collect earth, and return with it to sprinkle around their crops as effective protection from rodent damage. Could the soils of Mousa have such power? Currently, the RSPB guards against rodent colonisation by routine monitoring on the island and a contingency biosecurity plan for rapid eradication in the event of occurrence.
On Mousa, like anywhere in Shetland, bird migration can be hit and miss but when it is good it can bring great surprises. Numbers of migrating individuals are usually low, even on a good day, but species can be diverse. One House Martin and two Wheatears were the lot on my ‘worst’ spring day trip, but the best trip (20 May) produced 3 Great Northern Divers and a rare ‘blue morph’ Fulmar from the ferry, Whinchat, Redstart, Wheatear, Sanderling, Chiffchaff, Willow Warbler and Blackcap along the visitor path, then a Honey Buzzard - very scarce in Scotland - flew past at close range while I was admiring the view from the top of the broch. It is impossible to predict what might be seen, but during the migration seasons on Shetland, anything can appear.
Most people, even birdwatchers, do not often go looking for birds at night; however, twice a week from mid-May to mid-July, The Mousa Boat runs a special night-time ferry service to facilitate just this. The hoped-for species is the Storm Petrel.
During daylight hours there is little to show that the petrels are present. They nest deep in crevices and are only active on land at night, almost never seen at sea from land, rarely heard singing during daytime. In spring their distinctive, maritime fragrance has not yet permeated the inside of the broch, which is filled with it later in the year. However, as I leave the night ferry and begin to walk towards the broch at about 11pm (the date is 24 May 24) bizarre purring and hiccupping sounds start up from within a tumbledown wall. These are the songs of the petrels and are somehow evocative of a particularly unfrightening 1970s science-fiction film - hidden tiny creatures with spectral sonic-lanterns, suddenly coming to life.
I reach the broch and stop to look and listen with the other visitors, tonight the majority here with the two local nature and wildlife tour companies. The night is clear and the last beams of sunlight never completely fade, hinting at our proximity to the Arctic. Close in front of us, the imposing curves of the broch can be seen in detail, looming high into the dark purple sky.
Soon there is a flicker of black and white as a Storm Petrel scoots out from behind the broch, clearly visible but flying fast. The bird circles the tower a few times, then another appears, and another, all three spiralling together. Suddenly there is a fourth bird at the very top, moving quite differently. It is flying very slowly, hanging and slow-flapping in the minimal breeze, on tiptoe delicately pattering along the parapet. The combination of the tiny birds, mighty broch and soft midnight glow is spellbinding.
We return to the boat at about 1am, having seen perhaps thirty different petrels at the broch and heard many more singing from the island’s stone walls and boulder beaches. The atmosphere is tingling but everyone is hushed, as though we all share a secret. As the ferry quietly departs, a snipe begins drumming high above the island and for a short while the sweet, chlorophyll scents of the grassland herbs drift with us, out across the sound. The calm sea, prickled with silver stars, shimmers like the fringes of a dream. And my only wish is to go back.
Mid-June to mid-August is the busiest time for wildlife on Mousa. Sea mammals are seen frequently and breeding bird activity peaks. The island is at its greenest, days at their longest and in a land of golden perfection the sun would be warm and always shining and the sea forever calm and clear. But this is Shetland. And the weather is often poor, even in summer.
Whatever the weather brings though, once on the island, the upbeat buzz of seabird activity is impossible to dismiss. For some species, such as the terns, skuas and shags, the breeding cycle of individuals is not always tightly synchronised, so during a typical stroll in July it is possible to see a variety of young birds, ranging from small, newly hatched chicks to fully fledged, fresh-plumaged juveniles. Arctic Terns are a dominant feature in summer, their activity being particularly frenetic and vigorous. The tidal lagoons are a hotspot for this species and a brilliant place for both adults and children to experience the birds’ varied nesting, preening, feeding, courtship, and chick-rearing activities. Here the full age range of chicks, juveniles, first-summer, and adult birds occur all together and with binoculars or a telescope can be observed in detail for hours (when watching seabirds in high summer, it’s easy to lose track of time).
Since 2000, seabird breeding numbers on Mousa have been monitored by RSPB staff and volunteers using non-invasive, standardised techniques. During this time, like elsewhere on Shetland, breeding numbers have fluctuated and each year is different from the last. Logistical constraints dictate that not all species can be monitored annually; however, full censuses are carried out each year for Arctic Tern, Great Skua and Arctic Skua and maximum counts have totalled 1127, 41 and 14 occupied nest sites, respectively.Breeding numbers of Storm Petrels have been estimated using call-playback surveys and demographic modelling of the colony, the biggest in the UK. These methods indicated a substantial increase occurred between 1996 and 2008, from 5,410 to 11,781 occupied nest sites.
Summer can be a slow season for migrant birds. However, come July and August, waders are on the move and a few passage individuals can be found most days. Small parties of migrant Knot, Sanderling, Dunlin, Redshank and Ringed Plover are seen on the lagoons almost daily and after dark Golden Plover, Greenshank, Whimbrel, Curlew and Black-tailed Godwit can often be heard calling high overhead, heading for their wintering grounds. Migrant Common and Arctic Terns, beginning their long journeys south, also start to show up in July, with increasing numbers gathering on the shores of the lagoons until early August.
Throughout the late spring and summer Mousa is also visited by non-breeding seabirds - wandering young individuals not yet of breeding age and adults whose breeding attempts have failed early. Non-breeding skuas, gulls, shags and terns can usually be seen, loafing around the island in small groups. In July and August, non-breeding Storm Petrels visit too, numbers of which can be spectacular. These are mostly young petrels, typically two to four years old - ‘teenagers’ - which wander the north-east Atlantic in their thousands and at night prospect different islands for mates and nest burrows, prior to settling down to breed in later years. They visit land in greatest abundance during cloudy, particularly dark nights and can make a night-time petrel trip in July an even more extraordinary experience than a trip in May or June. Looking back through my diary notes, 17 July was a classic midsummer night.
Hot and muggy tonight (hay fever troublesome), the sea is hazy. Low cloud but no rain. Arrive at the broch around midnight and it’s buzzing. Scores of petrels calling and in flight, extremely close. The activity is swarm-like, manic. Constant flickings of air on my face as birds stream past. The swift shape of each is blurred by the darkness (very gloomy but not pitch). Birds forever coming and going like wisps of black smoke. Their white rumps twinkling then gone. Around the broch the wisps weave together into one living dark mass of incredible speed and grace - never scary, just uplifting. Many more birds than in spring; must be hundreds. On the way back to the boat the whole island seems to dance. Sound and movement around every stone.
Through August, the noise and throb of seabird activity gradually fades away, as more and more of the breeders and non-breeders depart the island to spend the winter elsewhere. This month marks the onset of autumn landbird migration in Shetland though, and is often productive for scarce and unusual species, such as Red-backed Shrike, Wryneck, Common Rosefinch, Greenish Warbler and Citrine Wagtail. By September, usually the only birds still breeding on Mousa are the Storm Petrels (which have an unusually protracted breeding period, sometimes lasting through to December); everything else is either a migrant or one of the few residents, such as the wrens.
On a calm day in early autumn, the island is at its most peaceful. The piquant spring and summer colours of the grassland have changed to warmer, amber tones and after a season of sharp intensity, the northern sunlight has mellowed and is easy on the eye. It can be an exciting time for seeing wildlife, but good weather becomes increasingly intermittent and therefore so too do ferry crossings. The last Mousa boat trip of the year is usually in mid-September.
On one day every year, usually in the second week of September, a sample of Storm Petrel nest boxes and crevices is checked on the island and the status of each nest site recorded. All located chicks of suitably large size are banded on one leg with a minute, uniquely coded alloy ring (allowing each bird to be individually recognised in future) and the nest data is used to estimate breeding success - the number of chicks fledged per egg laid per year. This study is run by the Shetland Bird Ringing Group and has been carried out by local ornithologists and volunteers every year since 1995. It is one of very few studies worldwide to band Storm Petrels of known age and thereby generate precise knowledge of the longevity of individuals, which, it has been discovered, live up to an astonishing 30 years old. I joined the group for the work one year, on 11 September.
The trip was timed to weather-perfection and come 10 o’clock, in warm sunshine, the ferry set off across Mousa Sound, soon to pass a pod of at least ten Harbour Porpoises gently rolling along through the calm blue surface. Once on land, the team split into two, and through the morning carefully checked Storm Petrel nest sites along separate sections of dry stone wall, and encountered young petrels of a variety of sizes. The largest juveniles were fully feathered, with a rather clockwork yet regal manner about them, uncannily reminiscent of albatrosses (although in miniature). The smallest chick was tiny, just a fluffy, fragile gathering of clean grey down with a little tubular beak slightly poking out. Such birds were not touched and the nest covering immediately replaced. The work was finished by early afternoon and we set foot back on the mainland just as the wind was strengthening and dark clouds began to gather.
Periodically there is a fashion, it seems, for TV wildlife documentaries in which the presenter touches charismatic wild animals and, in some cases, imparts that in doing so they, or “we”, feel close to nature. There’s no denying that if you hold a wild animal, physically you are close to it. However, the concept that by touching wild animals humans feel spiritually or emotionally close to nature strikes me as questionable and is at odds to my experiences of bird banding (which is though, after all, a method for scientific research). When briefly holding a bird while it is banded and measured, including juvenile Storm Petrels on Mousa, invariably I have never felt close to nature or the natural world. One reason for this, among many, is that when holding a wild animal the big thing that one simply cannot know for certain is that it really needs and wants to be touched - and I just find it impossible to feel genuinely close to something, emotionally or spiritually, if there’s a chance that actually it might want rid of me.
By contrast, the one circumstance when I sometimes do feel spiritually close to nature is when I am watching things from a calm location (perhaps hidden on a rock, looking from a distance) and am confronted by an aspect of non-human life that catches my interest so completely that, for a brief time, I lose all consciousness of my physical existence and feel totally anonymous, connected to the natural surroundings because I’ve left the human world. This sensation, for it is really nothing more, has been described by the wildlife artist Lars Jonsson as ‘the dissolving’ - its essence elegantly and beautifully there captured.
It is a credit to those who help manage the island as a nature reserve, that Mousa, as it turns out, is a place where the dissolving is particularly easy to chance upon. And it is this, inherently coupled with the diverse gatherings of life which occur there every year, that makes the island a jewel: special, rare and worth experiencing, in daylight and at night.
Armit, I. 2003. Towers in the North – The Brochs of Scotland. The History Press, Gloucestershire.
Bolton, M., Brown, J.G., Moncrieff, H., Ratcliffe, N. & Okill, J.D. 2010. Playback re-survey and demographic modelling indicate a substantial increase inbreeding European Storm-petrels Hydrobates pelagicus at the largest UK colony, Mousa, Shetland. Seabird 23: 14-24.
Okill, J.D. & Bolton, M. 2005. Age of Storm Petrels Hydrobates pelagicus prospecting potential breeding colonies. Ringing & Migration 22: 205-208.
Pennington, M., Osborne, K., Harvey, P., Riddington, R., Okill, D., Ellis, P. & Heubeck, M.2004.The Birds of Shetland.Christopher Helm, London.
Ratcliffe, N., Vaughan, D. Whyte, C. & Shepherd, M. 1998. The status of Storm Petrels on Mousa, Shetland. Scottish Birds 19: 154-159.
Walsh, P.M., Halley, D.J., Harris, M.P., del Nevo, A., Sim, M.W., Tasker, M.L. 1995. Seabird monitoring handbook for Britain and Ireland. Published by JNCC / RSPB / ITE / Seabird Group, Peterborough.
My thanks go to Helen Moncrieff, Mark Bolton and Newton Harper (RSPB Scotland), Dave Okill (Shetland Ringing Group), Howard Towll (www.howardtowll.com), Ian Andrews (Scottish Birds), Ann Sinclair (Fair Isle Museum), Mike Pennington (Shetland Bird Records), Rory Tallack and Paul Harvey (Shetland Biological Records Centre).
Will Miles is based in North-east Scotland. He is passionate about Scottish Islands, seabirds and bird migration. His interest and employment in the field of birds and nature has led him to a diversity of island locations during the past decade, for example Hokkaido, the Falklands and Ascension Island, and in Scotland, the Outer Hebrides, Skye, Orkney and his favourite island archipelago, Shetland.
Header image shows the Broch of Mousa on a warm, calm night in early summer. Photograph by Will Miles.