Celebrating World Environment Day

Why do seabirds usually nest on islands?

Well, it’s handy for the food shopping and they can fly, but the main reason is because there are no land predators there. It’s not much fun popping out for a fish supper if you’re forever worrying that your young will become the victim of some furry serial killer while you’re away.

There are many islands up and down the coast of Argyll that used to be noisy tern colonies but are now empty. The reason behind this is the arrival of American mink, which can devastate a tern colony in just a few days. These mink are not native to Scotland and, for reasons that we don’t fully understand, they impact seabird colonies in a way that our native predator, the otter, does not.

Another unwelcome land predator that can turn up on islands is the brown rat. We became aware of the effects that rats were having on the seabirds on Canna in the early 2000s. Having secured funds from Europe and Scottish Natural Heritage, we spent nearly half a million Euros on getting rid of these predators in a highly successful operation during 2005–06. Since then, a number of the seabird populations on the island have started to increase.

We’d rather not have to do that all over again, not least because it would cost considerably more next time. The solution is to ensure that rats don’t return – we have put in security measures at the harbour to prevent them arriving as stowaways on ships or in cargo, and we have contingency plans to deal with them rapidly if they’re detected. We refer to this as biosecurity.

The island of St Kilda currently has no land predators but the military facilities on the island are being rebuilt in a 3-year project. This involves shipping huge quantities of building materials out on a landing craft. Aware of the significant danger of introducing rats and other unwelcome visitors with this cargo, we developed a comprehensive programme of biosecurity measures with the contractor, Galliford Try. These included inspections, traps and baits on board the vessel, a trap cordon on St Kilda, and poison stations around the loading facility on the mainland. We even arranged to shift the location of the shore base 130 miles up the coast to Kishorn because we were concerned that the site originally planned carried too high a threat of invasive species.

All this vigilance paid off. In the summer of 2018, signs of rodents were detected on the landing craft while it was en route to St Kilda. Following the agreed procedures, it was turned around and returned to the mainland until the culprit, a mouse as it turned out, was located.

Scotland is particularly blessed with seabirds. We have nearly half of all of the seabirds breeding in the European Union here. And the Trust cares for a disproportionate number of these breeding sites, from St Kilda and Fair Isle (two of the largest colonies in the eastern Atlantic) to Mingulay, Canna, Staffa and Iona. Many of these are on islands designated as being of international importance for seabirds: Special Protection Areas.

Over the next three years we plan to review the biosecurity measures needed on all of these islands and to strengthen them. A big part of this will be raising awareness among the visiting public and operators of commercial vessels of the need to be vigilant. We must all treat these precious islands with the care that they undoubtedly deserve.