Guano Gwales

The white patch on the island of Grassholm (Welsh: Ynys Gwales or Gwales) is not snow, limestone, or any type of rock for that matter. In springtime, half the island is covered in gannets and their associated guano (also known as bird shit). About 12% (equivalent to 40,000 birds) of the world’s population of gannets live on Gwales; the other 78% can be found nearby on the islands of St. Kilda and Bass Rock off the coast of Scotland. A big problem for these birds nowadays are floating islands of plastic. Instead of seaweed, the gannets now use fishing nets and all sorts of plastic rubbish for nesting. Around 65 birds die annually from plastic entanglement. Like the islands of Skomer and Skokholm, Gwales is of volcanic origin. Basalt dominates, with sporadic occurrences of felsite, mugearite, and rhyolite dating from the Silurian (around 440 million years ago). The sediments and rocks on these small islands can be related to mainland Wales. It is believed that at least Skomer was separated from the mainland by erosio during the last Ice Age.

Gwales is mentioned in the Mabinogion, a collection of medieval Welsh manuscripts drawing back from Celtic and Iron Age mythology. In one of the stories the severed head of Bran the Blessed is brought to the magnificent castle that stand high above the ocean on Gwales. Bran’s head is kept alive for a mere 8 years, while his seven companions feast non-stop in the great hall of the castle. In 1972 archaeological research revealed field boundaries and a small settlement with round houses and rectangular buildings in the middle of the island. Interestingly the blanket of gannet guano had killed the grass which in turn revealed the archaeological remains. The remains are believed to date from the Middle Ages and thus could represent the mythological feasting hall.

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Image: Courtesy of S. Murray. Aerial photo of Grassholm.

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