Scotland’s seabird pirates in peril

04 Sep 2024 | No. 2024-24

A new study led by the British Trust for Ornithology in Scotland (BTO Scotland) has unveiled the migration routes and wintering grounds of one of Scotland’s rarest and most endangered seabirds – the Arctic Skua. These discoveries are a crucial step towards understanding the threats these seabirds encounter when they are far from Scotland’s shores, and the steps we need to take to conserve them.

During summer, Scotland’s coasts and islands provide a haven for breeding seabirds, from Puffins and Guillemots to Kittiwakes and Gannets. While Scotland hosts numerous bustling colonies, many of our seabird species are in decline and often much of our attention is focused on pressures experienced during the breeding season. However, seabirds spend only part of the year at these colonies – as autumn arrives, there is an eerie silence as birds leave and head out to sea. But what dangers do they face once they depart our shores? The key to addressing this question is in understanding where seabirds go outside of the breeding season.

Arctic Skuas are attractive and impressive birds. Their preferred way of feeding is by stealing from other seabirds, which they relentlessly harass with remarkable agility and grace. Pursuing smaller species such as Puffins, terns and Kittiwakes, the oceanic pirates do not give up until their chosen victim has either surrendered a beak full of seafood or disgorged the fishy contents of their stomach. Sadly, despite their apparent invincibility, Arctic Skuas are the fastest declining seabirds in the UK and are on the Birds of Conservation Concern Red List. Scientists from BTO Scotland have been trying to better understand their movements and conservation needs through fitting miniature, long-term tracking devices to individuals nesting on Fair Isle in Shetland and Rousay in Orkney.

Amazingly, this work revealed that skuas from both Fair Isle and Rousay, which are no further than 90 km apart, wintered thousands of kilometres away from one another. Some migrated to the Canary Current off West Africa, while most travelled further into the Southern Hemisphere, wintering off south-west Africa or south-east South America – covering distances of over 10,000 km.

The study also mapped the routes taken by the skuas during their long migrations and pinpointed crucial refuelling areas where birds stopped to rest and feed during their journeys. After departing their breeding colonies in autumn, most Arctic Skuas headed south through the North Sea and English Channel, continuing along the Iberian Peninsula before heading south further still. In contrast, during spring migration, the skuas all converged on an important feeding hotspot in the mid-North Atlantic Ocean, where they could feed up ready for the upcoming breeding season back in Scotland.

Dr Nina O’Hanlon, Senior Research Ecologist at BTO Scotland, said “By identifying where these wide-ranging seabirds spend their time away from Scotland, we can begin to uncover the threats they may face, and how these may impact the skuas’ survival and future breeding success.”

She added “This knowledge allows us to prioritise future research and conservation actions to protect this charismatic seabird”.

BTO research was funded by several generous individual donors. The paper's authors would like to thank everyone who helped with fieldwork and all landowners, including Fair Isle Bird Observatory.
Helen and David Aiton, who contributed to work on Rousay, were supported by grants from the Scottish Ornithologists’ Club and British Birds Charitable Trust.

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