26 Nov 2020

Paperclip-sized tracker reveals intrepid journey of UK’s smallest seabird

Mark Bolton, Principal Conservation Scientist at the RSPB (BirdLife in the UK), explains how a satellite tag the size of a paperclip gave us important new insights into the life of the small but tough European Storm-petrel, and how these discoveries can help us protect it.

European Storm-petrels regularly travel more than 200 kilometres to find food © Peter Steward
European Storm-petrels regularly travel more than 200 kilometres to find food © Peter Steward
By Jessica Law

Why had researchers been unable to track the European Storm-petrel until recently?

European Storm-petrels Hydrobates pelagicus are extremely small – the size of a sparrow, and the second smallest seabird in the world. High-precision GPS tags for such a tiny species have only become available in the last few years. The trackers we used weigh less than a gram and can record the bird’s location to a precision of a few metres, anywhere in the world. Over a four-year period, we tracked 42 Storm-petrels nesting on the island of Mousa in the Shetland Isles, UK.

What were your most important findings?

We found that although storm-petrels have a large foraging range, regularly travelling more than 200 kilometres from the colony, they consistently used a relatively small area of sea, much of which has already been identified as a Marine Protected Area due to its importance for other species. With our new data, we determined that the storm-petrels’ daytime foraging area, and the waters immediately adjacent to the colony where birds commuted back and forth, both met the criteria to be considered as marine Important Bird & Biodiversity Areas (IBAs). Since storm-petrels only visit their colony during darkness, their ‘commuting areas’ would not have been detected using conventional visual survey methods.

Were there any surprises?

One of the birds we tracked was caught in a strong gale and blown across the North Sea to Norway, taking shelter in a fjord just north of Stavanger. When I caught it following its return, I found that it had gained weight during its trip and that its chick had been fed. So the bird had not merely survived being storm-driven to Norway, but had managed to find food en route, both for itself and its nestling. It is likely that all the birds out feeding on that day endured the same conditions. In fact, storm-petrels are so-called because they are usually only sighted near land during strong winds.

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How can this study help protect the European Storm-petrel and other seabirds?

The birds we tagged are part of the largest colony of storm-petrels in UK, which is an internationally important protected area. In principle, all storm-petrels breeding at this colony are therefore also protected when they are feeding at sea. However, if we don’t know exactly where they feed, it is very difficult to assess potential impacts of marine activities and enact this protection. This study provides the information we need to do so. Furthermore, the areas that qualify for marine IBA status can now be recommended for statutory protection. Both areas coincide with Marine Protected Areas designated for other reasons, emphasising the importance of certain sites for a whole range of marine biodiversity.

GPS tracking reveals highly consistent use of restricted foraging areas by European Storm-petrels Hydrobates pelagicus breeding at the largest UK colony: implications for conservation management is published in Bird Conservation International.