When I first visited Shetland 11 years ago, one of the many highlights was a dusk trip over to the small island of Mousa, an RSPB reserve. Mousa is famous for two things. The first is the most complete Iron Age broch still standing, of which more in a moment. The second claim to fame is the fact that hundreds of European storm petrels nest within the walls of said broch each summer. After moving to Shetland earlier this year, I knew that this magical trip to Mousa was one experience I needed to repeat, and that is just what I did recently.
Broch of Ages
First things first, what is a broch? These enigmatic round towers are found across Scotland, in varying states of repair. You can still see the circular structure of some, whilst all that remains of others is a mound, pile of rubble or a hint from a place name. Caithness, Orkney and Shetland are particular strongholds. There is evidence for approximately 120 across Shetland alone. They were built in the 500 years between 400 BC and 100 AD.
The towers were large, roughly circular drystone buildings, with multiple floors and possibly a conical thatched roof. To support such a tall structure without mortar, the builders made the walls at the bottom extremely thick. They then made them progressively thinner as the building rose to reduce the weight.
Incredibly, despite being studied intensively for over 200 years, there are still arguments about what brochs were used for. As there are no written records from the builders themselves, there have been a number of theories, including that they were purely defensive. More recent research suggests that they were used for a number of activities. They were living spaces, grain stores and even places to inter relatives.
Mousa broch was likely built around 300 BC. At 13 metres tall, it is a real landmark, and is clearly visible across the sound from the mainland. It is by far the best preserved of Scotland’s brochs.
European Storm Petrels
Mousa’s famous summer visitor is the diminutive storm petrel, or alamootie in the Shetland dialect. These are small seabirds, not much bigger than a house sparrow and are related to shearwaters, fulmars and other tubenoses. European storm petrels are very dark all over except for a white rump and pale band under the wings.
Despite their small size, they winter out at sea in the Atlantic off South Africa and Namibia. They only come to land in the summer months to breed. Most breed on islands off the coast of Europe. They can’t survive anywhere with predators such as rats or cats, so Mousa is the perfect place for a colony as it is free from both.
Approximately 11,000 pairs breed across Mousa, which is one of the more accessible places to see and hear them. Of these, about 300 pairs nest within the drystone walls of the broch itself, a truly remarkable high-rise residence. The rest raise their single chick in the gaps between boulders on the shore or in drystone walls across the island. Because of their vulnerability to predation by great skuas (bonxies) and great black-backed gulls, they only visit the nest site at night. Which is where the evening boat trip comes in.
Shetland’s Simmer Dim
Guided storm petrel trips over to Mousa run between late May and mid-July. Trips don’t leave Sandwick until around 10.30pm. This is because of Shetland’s position so far north. In the summer months, dusk doesn’t arrive until after 10pm and it never gets completely dark. This is known here as the simmer dim, which translates as ‘the twilight of a summer evening’. Consequently, the storm petrels have to wait until later in the evening to return to their nests if they are going to get any sort of cover at all.
Our recent trip was sold out; the trips are becoming increasingly well-known and popular, and you definitely need to book. We had lucked out with the weather. It was calm with a bit of cloud, perfect for storm petrels. Once on the island, our excellent guides Rodney and Darren took us in two groups on the walk to the broch, giving us some of the island’s history on the way. As we walked, we could hear multiple snipe chipping and drumming.
Surrounded by Stormies
Storm petrels take turns on the nest, and we were hoping to see birds returning to their partners. As we got to the broch, we could see the first birds flying in, flitting around us and the broch. As time passed, more and more birds arrived and the experience felt very much like being at a bat roost, but with more noise. Birds on the nest make a curious churring, hiccoughing noise to call to their mate and this got progressively louder and louder. Sometimes, birds got the wrong nest hole and had to make a swift exit again. Not very dignified!
After a blissful hour or so surrounded by storm petrels, we walked back to the boat. It was past midnight by this time, but there was still some golden light on the horizon. As we passed some of the island’s walls, we could hear more of the petrels churring. This was a perfect end to a perfect evening.
Further Reading
Daytime boat trips to Mousa run six days a week from April to the end of September. The guided evening storm petrel trips run on selected days from late May to mid-July. You can find booking details and lots of information about the island on the Mousa Boat website.
Although not in Shetland, the Caithness Broch Project charity was set up to celebrate the fact that Caithness has more brochs than anywhere else. They are raising funds to rebuild a broch using the same techniques the original builders used and hope to provide new insights into brochs generally and Iron Age life. Their website is a wonderful resource, and you can also donate to their cause.
On that same trip 11 years ago the magic of the experience still lives with me.