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Leach’s Storm-petrels in Shetland – New discoveries

Posted by Brydon Thomason on Monday 16th August 2010 | Birding in Shetland

Since the discovery of Leach’s Storm-petrel breeding colonies in Shetland in the late ‘70’s and early ‘80’s, on Foula and Ramna Stacks, surveys of the species have been infrequent. Although additional breeding colonies have long been suspected, no attempts had been made recently to survey ‘potential’ sites (most relatively inaccessible), nor had time been dedicated to attempt to tape-lure the species for ringing in the north of Shetland, away from the known breeding sites. This summer, however, Will Miles, fellow Shetland Nature team member Rory Tallack, and I set out on what was to become a pioneering discovery.

Prior to this summer, Will had worked on Leach’s Storm-petrels on St Kilda for four consecutive years. Although there are few better places than St Kilda to undertake work on the species, Shetland had the distinct appeal of ‘the unknown’, and we hoped that our belief in finding Leach’s in the north would ring true. Specifically, we planned to try new sites for tape-luring birds for ringing (under BTO license); also, to visit some of the more remote islands and stacks around Unst and Yell in the hope of discovering new breeding colonies (under SNH schedule 1 species license).

With Shetland Nature’s local knowledge and contacts, I was thrilled to help lead the adventure and to organise our visits to the off-shore sites, where, in many cases, only a mere handful of people had ever set foot before – a thought which had tantalised me for many years! Birders like me, by nature, are driven and inspired by the prospect of discovery, by thoughts of ‘pushing the boundaries’ and by any possibilities for pioneering study. In the end, it was a mixture of these motivations, our adventurous spirit, and our unerring enthusiasm that fuelled an exhilarating week, ultimately rewarded by the discovery of Leach’s Storm-petrels nesting at a new site in Shetland…

Tape-luring and mist-netting Leach’s Storm-petrels for ringing

Previously in Shetland, Leach’s Storm-petrels had been trapped for ringing mostly on Foula and indeed Fair Isle, where individuals are caught and ringed almost annually by the bird observatory staff. Peak time for catching the species using tape-lures is mid-July to the first week of August. To my knowledge, no successful attempt had ever been made to tape-lure Leach’s Storm-petrels on Unst or Fetlar; therefore, it was with great optimism and enthusiasm that we set out to do what had never been done before on these islands.

Over the course of the week, to our great surprise, we successfully caught and ringed Leach’s Storm-petrels on every night that mist-netting was attempted (five in total). Ten birds were trapped in all: one on Fetlar and nine on Unst. On Fetlar, we attempted mist-netting on only one night and, remarkably, a Leach’s Storm-petrel was the first bird caught – the first ever record of the species for the island! An additional 22 European Storm-petrels were also trapped that evening.

What was very interesting was that many of the Leach’s on Unst and Fetlar, which were trapped or heard calling around the nets, came in to the tape-lure relatively early in the night, well before midnight. This was in contrast to the situation on Fair Isle and St Kilda, where birds have rarely ever been seen so early, and the vast majority have been caught much later, between 1am and 3am. One possibility to explain this may be that in the far north of Shetland, for some reason, in the early evening more birds occur within relatively close proximity to land than do elsewhere.

In a sense, we had begun to re-write the mist-netting status of the species in Shetland: our preliminary results suggested the far north to be a much more lucrative and reliable area for catching birds than any other area or island previously tried. With this idea in mind, we set out on our first excursion to try to find a new breeding colony on one of the unexplored offshore islands and stacks in the North… a find that would be the ‘icing on the ornithological cake’ for us!

Pioneering discoveries

During the course of the week we landed on several off-shore stacks and islands, one of which Dave Okill (regional BTO officer) joined us on. This in itself was an exhilarating experience, especially landing on Muckle Flugga, where we found European Storm-petrel to be present and calling from suitable nesting habitat underground.

There was something very special about just getting onto these normally inaccessible Isle’s, knowing that in many cases only a very few people had ever been on the land before. It was on one of these landings that we made the most momentous and to us epic discovery of all though – a previously undiscovered colony of Leach’s Storm-petrels! After all our self-motivated efforts, this truly was a just and gratifying reward. More on this breeding discovery soon…