Storm Petrels in the Simmer Dim

by | 28 Jul, 2023 | History, Landscape, Nature, Travel, Weather | 0 comments

The boat is already laden with people. We’re not late, but perhaps this is one of those instances where arriving half an hour early was the correct thing to do. I dash down to the owners, who are standing at the land end of Sandsayre Pier, near Sandwick on Shetland, and tell them my name. Thankfully my booking, made online over a month ago, was recorded and my friend Simon and I are on the list for the trip. I pay, and we squeeze into the last remaining seats on the boat. Two minutes later, the Solan IV heads out across the water.

The journey to the island of Mousa (pronounced moosa) is short yet enchanting. Everything is caught in the Simmer Dim, the long-lasting twilight of northern summers. Earth’s shadow shades the eastern horizon lavender blue, while westwards the horizon is tinted peach, capped with a lid of fading azure. It’s heading towards 11pm, but there’s no need for torches. The afterglow of sunset, which happened at around 10.20pm, is bright. Light abounds. It bounces off the sea, off the rocks of a shallow beach on the island and off the white feathers of a Fulmar which glides alongside the boat. Our eyes are filled with lustre, a soft and seamless gloaming which seems to hold us, suspended. This, then, is the gift of Baldur, Norse god of light. I have often wondered what it would feel like to be mantled in a twilight which never gives into the dark. Now I am in it, sleep deprived after a sleepless ferry crossing from Orkney, aware that my mind needs rest but so entranced by this in-between time that the few hours it will last don’t seem long enough. There is such lucidity here. The Dim seems somehow, impossibly, clearer than the day.  

Mousa, Shetland, Simmer Dim by Kerrie Ann Gardner

Once on the island, we learn that the stony beach near our landing spot was once used to dry and cure Cod, and of the terrible conditions the crofters of Shetland had to endure under the control of their lairds, land owners who demanded an unequal share of crofter’s produce leaving them in extreme and merciless poverty. Change came with the Crofting Act of 1886, brought about in part by rebellion across Scotland. Crofters refused to pay rent and defiantly occupied land which the lairds had earmarked for hunting or sheep. It would be nice to think that such times have moved on but in a sense they continue. Living conditions have improved, but land ownership in Scotland, along with the rest of the UK, is still pitifully unequal.

As we pass the beach and head south, I hear curious calls beneath the stones, calls that are alien to me. Inland, the voices of numerous seabirds rise and fall. I struggle to identify these too. We pass the ruins of Haa, a house built in 1783 by once owner of the island James Pyper. Pyper built this home for his wife Janet to keep her from alcohol, but she had it smuggled in by fishermen and drank herself to death. Pyper’s second wife, Anne, had no such dependence, and lived happily on Mousa until her death in 1852, convinced it was the loveliest place on Earth. I was struck by this story, not just for its tragedy but for its reflection of the human mind – how the same environment can cause one person such misery while another finds such joy. 

Mousa, Shetland, 60º North bench photograph by Kerrie Ann Gardner

At 60º, Mousa lies on the 60th parallel, a line which is 60º north of the equator and 30º south of the North Pole. The same line cuts through Helsinki, Oslo, the southern tip of Greenland and slices through Canada’s Hudson Bay. Standing by a bench made of driftwood to mark this line on Mousa, we’re told that if it wasn’t for the Gulf Stream, Shetland would be much colder. The movement of warm water across the Atlantic keeps this northern archipelago fairly temperate, especially when compared to areas on a similar latitude, such as southern Yukon Territory in Canada, where the average December temperature is -16.5ºc. Shetland’s average December temperature of 2ºc seems almost warm in comparison. 

Mousa Broch, Shetland. Photograoh by Kerrie Ann Gardner

The most prominent feature on Mousa is the Broch, known in old Norse as ‘Mósey Jarborg’ – Tower of Mousa. It’s a thirteen metre high Iron Age roundhouse and the most well preserved of it’s kind in Scotland. It’s an imposing structure, built some 2,000 years ago, with 5m thick stone walls and a staircase leading up to the top with stairs so short that they seem more suited to children’s feet than adults. And it is here that we stopped, for this is where the Alamootie nest. 

Alamootie is the Shetland name for the Storm Petrel, and Mousa is home to around 12,000 of them, 40% of the British population. Many of these birds nest within the sturdy walls of the Broch, but others have made homes within the dry stone walls of the island and under stones on the beaches. They have an admirable life, spending most of their time far out at sea hanging just above the waves as they search for prey. The name Petrel is thought to be a corruption of ‘pitteral’, for their pitter-patter movements across the water. They are related to Albatrosses and Shearwaters, which also have ‘tubenoses’, adaptions on their beaks used for salt excretion and for the detection of food in the open ocean. It is thought that this advanced olfactory system is what enables the Storm Petrels to sniff out their waiting partners on Mousa in low light. 

Storm Petrel sketch by Kerrie Ann Gardner

Storm Petrels are small. Their wingspan is around 36cm and they weigh no more than 38g, the equivalent of three £2 coins. But their diminutive size belies their resilience. Unlike many other birds, a Storm Petrel egg can be left unbrooded for days at a time without perishing. Similarly the chicks, if left for long periods, can enter a kind of torpor, appearing dead until they are revived with an oily regurgitation from their parents. Incubation is shared by the parents and can take 40 to 50 days, considerably longer than the incubation of Passerine eggs. One parent stays with the egg for 3 to 5 days at a time while the other forages far out at sea, beyond the reach of most predators, meaning that the remaining bird loses a considerable amount of weight by the time its mate returns to relieve it. Once the egg hatches (and there is only ever one egg) the parents brood the chick for a week and then only return to the nest to feed it. At around 50 days old, the parents limit the amount of food given to their chick until they stop visiting completely. Then, some 60 to 80 days after hatching, the young Petrel must make its way out of its nest chamber alone and find its way across the ocean without any guidance from its parents. (They are known to travel as far as the South Atlantic and the Indian Ocean.)

As we approached the Broch, strange voices started to emit from the stones. They were the incessant calls of sitting adult Storm Petrels, hungry and eager to feed. The sound is unlike anything I’ve heard before and it’s difficult to translate it into English, but it’s akin to a grating churr followed by a higher-pitched ‘chaaw’, with a consistency that would put even a Nightjar to shame. Kiiiiiiiiiiirrrrrr-chaaw, kiiiiiiiiiiirrrrrr-chaaw. It was surprisingly loud, perhaps because the brooding birds were so desperate to leave, or perhaps because their chambers within the Broch acted as amplifiers. It may well have been a combination of both. I dared not get too close, but I was assured that the presence of a group of humans wouldn’t disturb the birds. In fact, us being there meant that fewer predators, such as Great Black Backed Gulls and Great Skuas (known locally as Bonxies) were likely to visit the colony. 

Mousa, Shetland, Storm Petrels at the Broch photograph by Kerrie Ann Gardner

Sure enough, a few minutes later, the first returning Storm Petrels began to appear off the sea, unfazed by us onlookers. They come in under the cover of dusk in an attempt to avoid predation. I was struck by how Bat-like they were, Bat-like yet Swift-fast. Again and again the returning birds circled the Broch, reminiscent of Bats returning to their roost before dawn, flitting towards holes in the half-light that we couldn’t see, homing in on the voice and scent of their mate. Their behaviour was so much like a colony of Bats that I wondered if they might use echolocation to aid the detection of their nest holes, but a study by Ranft and Slater in 1987 concluded that Storm Petrels do not use ultrasonic calls. 

The majority of our group fell silent so that, save a few persistent question askers, all that could be heard was the lapping waves and the calling birds. Petrels continued to come. Some narrowly missed our heads. Occasionally, I would watch as one found its nest hole and shuffled inside, consumed by darkness. The sky behind the Broch continued to glow. Simon showed me his watch. It was 12.02am. I scanned the sky and saw only one star, Arcturus, in the constellation of Boötes, Guardian of the Bear. The Bear, the constellation Ursa Major, was nowhere to be seen, drowned out by the Simmer Dim, so the Guardian watched over us instead. 

I don’t know how long Simon and I sat watching the Storm Petrels as they returned to the Broch, but I do know we found it difficult to move. He is not as interested in birds as I am; the Storm Petrel trip was my idea and once I’d booked it I felt a little guilty for booking him on too, even though he agreed, worried he might not find it as absorbing as I would. But it turned out that he was just as spellbound as me. 

Mousa Broch, Shetland. Photograph by Kerrie Ann Gardner

Eventually, I reluctantly suggested that we should go into the Broch, as it seemed remiss to be so close to an open Iron Age structure without at least poking our heads inside. As we huddled down to pass through the low entrance we could hear the Petrels from all sides. Climbing the staircase to the top in near total darkness was a shock after the outside glow of the Simmer Dim, and the stairs had such small tread that is was easier to scramble up than walk. After we walked around the top, we turned to descend and found a Petrel perched on the stairs just below us. It was incredibly Swift-like – if it wasn’t for the white rump which was reminiscent of a House Martin, in the half-light it could almost be mistaken for a grounded Swift. I watched in fascination. It shuffled forwards a little, evidently unable to walk (again, like a Swift) before it suddenly disappeared down into the Broch and we cautiously followed. 

Mousa Moonrise. Photograph by Kerrie Ann Gardner.

Once we were back outside, we rounded the Broch and there, just leaving the eastern horizon, was the rising half Moon, burnt orange against a smoke-blue sky. Seabird’s voices still ebbed and flowed from inland, and the Storm Petrels continued to arrive, quick-winged silhouettes under a still-bright sky. 

Mousa noctilucent clouds. Photograph by Kerrie Ann Gardner

As we walked back to the boat, we occasionally paused to listen to the Storm Petrels nesting in dry stone walls, sounding like little witches in the dark, chanting. Faint noctilucent clouds began to appear above the small hills of Mousa, but they were so indistinct that I wondered if they were perhaps only cirrus clouds. I didn’t want to leave. I knew I was tired, as the boat crew must be too, but the magic of this little island, held as it was by a still, clear twilight and the voices of many birds, was beguiling. I wondered what time the Storm Petrels would stop coming, what level of brightness they would deem unsafe, and thought of the hungry Petrels off across the sea as their mates settled down on their single egg. How would the island look as the first rays of sunlight fired the lichen on the dry stone walls gold and painted a dazzling path across the sea? Would the other seabirds respond, their calls increasing as the light intensified? And how did Mousa feel in the daylight? Did it retain its charm under the Sun’s full glare? So much to find out. But alas, we were meticulously counted back onto the Solan IV, making it impossible for sentimentalists like me to surreptitiously slip away. 

Back at Sandsayre Pier, I shook the captain’s hand and thanked him for our trip. I had not expected to be taught about the history of Mousa and was grateful for his knowledge. As we climbed into Simon’s truck, I watched Solan IV head back out to sea, her lights shining on the glassy waves, and felt a longing for such an existence, to be always surrounded by water and birds. 

Town Hall, Lerwick, Shetland, with Noctilucent Clouds. Photograph by Kerrie Ann Gardner

We arrived back to our hostel in Lerwick at about 01.40am. I knew I should sleep, but with the coming dawn the noctilucent clouds had brightened. They now hung above Lerwick Town Hall like electric blue ripples to the sky. Simon turned in, but I sat for some time on the landing, quietly looking out the window as the Earth tuned, caught up in this final finale of Shetland’s Simmer Dim. 


P.S. Please excuse the poor quality of some of the photographs in this piece. They are a mixture of handheld DSLR shots (hence some blurring) and phone photographs.


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