Paul Walton, Head of Species and Habitats for RSPB Scotland, brings us this blog on island life, the species that live there, the pressures they face and the work going on to protect them ahead of the World Island Invasives Conference which is taking place in Dundee next week. 


Everyone knows what an island is – a piece of land surrounded by water. But actually defining the idea can be tricky, with the continents themselves surrounded ultimately by sea, some islands becoming joined to the mainland at low tides, whilst some others completely vanish at high tide.

The basic factor, though, is that an island is a place apart, a piece of land that stands alone, separated from the rest of the wider terrestrial environment. This condition means that life proceeds in relative isolation and, because of that, develops special, sometimes unique characteristics. Naturalists and biologists have appreciated this special nature of islands for centuries, and studying the wildlife of islands has revealed many truths about the wider nature of life on our planet - most notably, of course, following Charles Darwin’s seminal visit to the Galapagos archipelago in 1835.  

When it comes to the conservation of nature, that specialness reaches new heights. Islands occupy only about 5.5% of the world’s land area, but contain more than 15% of all terrestrial species, 61% of all recently extinct species, and 37% of all critically endangered species. Understanding this, and tackling the issues facing island wildlife, are thus essential elements of our collective responsibility towards the natural world.

One critical part of island ecology is that species living on islands are often freed from the pressures of many of the competitors, diseases and, in particular, predators, that they would face if they were living on continents.  For instance, most of the world’s 346 species of seabirds nest in colonies, on islands – known as seabird islands - and most of these species are heavily dependent on predator-free islands as breeding sites.

When people, accidentally or deliberately, introduce non-native predatory animals – principally rats, cats, snakes, stoats, ferrets and even mice - onto seabird islands, the effect can be devastating. Seabirds are the most threatened group of marine animals in the world, with around 29% of species classified as threatened – and most of these breed on islands. In Scotland, its thought that at least 13 colonies of the Manx shearwater alone, a beautiful bird of which around 40% of the world population breeds in Scotland, have been lost in recent centuries, mostly due to rat introductions to seabird islands.

Thankfully, there is much that can be done. First, we can take action to prevent the release of non-native species onto islands. This is called ‘island biosecurity’, and either prevents deliberate introductions (through education and awareness raising), or reduces accidental introductions from boats, transport and trade (through training, surveillance and trapping). Then, we can undertake projects that remove invasive non-native species that have already been introduced to islands by people – called ‘island restoration’ projects. Together, these measures can protect and restore island wildlife, with spectacular results. 

About 80% of islands in the UK are in Scotland. These islands support globally important seabird breeding populations, and those populations are in trouble. One of the main causes is deep and fundamental shifts in the marine food-chain driven by human-induced climate change. Recent decades have seen the biomass of key zooplankton species plummet by more than 70% in the NE Atlantic. Climate change is warming the sea surface and this is generating asynchrony in the timing of zooplankton breeding, and the timing of the annual phytoplankton bloom on which they graze.

The system is out of seasonal synchrony and, to compound this, nutrient-poor warm water plankton species are beginning to replace the nutritious cold water species. The zooplankton is food for the key seabird prey fish - sandeels – and fewer sandeels is the result, with inevitable knock-on effects on the breeding success and survival of their predators, the seabirds.

The effect is patchy and varies between years – but the recent decades have seen more poor food years for seabirds than previously, indicating a long term shift in our seabirds’ core prey-base. Seabird breeding is failing, particularly in Shetland and Orkney where, for example, kittiwakes have declined by over 90% in recent decades. And many of the seabirds that do breed are now having to travel record distances to find prey to feed their young.

Faced with a shifting and diminishing food supply, and the intractable nature of climate issues, what can we do for Scotland’s seabirds? The answer is we can protect and restore as many island breeding sites as possible. This is essential climate change adaptation for our precious wildlife. By maximising seabird breeding opportunities around our coasts, we are giving these birds the best possible chance to exploit the food that is present. We thus build resilience in our globally significant seabird populations to the challenges we know they will face in future.

This month, the University of Dundee is hosting the World Island Invasives Conference, 2017. This event will bring together the world’s expert academics, practitioners, ecologists and officials to share experiences of island restoration and biosecurity. Dundee University staff have been leading the rat eradication on South Georgia, perhaps the world’s most important seabird colony and one of the most challenging island restoration projects ever attempted.

It is a hugely timely and exciting event, which will, I hope, signal the beginning of a step-change in island biosecurity and restoration work in Scotland, other parts of the UK, the UK Overseas Territories and around the world, learning from past experience and building on best practice. Let’s hope that by coming together, people can work meaningfully and constructively to protect island wildlife from the huge pressures we, collectively, have placed upon it.