While foundations are being laid, noise scares fish and whales away but, once the generators are up and running, wild creatures return.
Migrating land birds are vulnerable if they blunder into a forest of rotating giants but the overall risk is low. Seabirds spend long periods near wind-farms but most species fly so low over the water that they’re at little risk from turbines. Gannets may be an exception; they fly at collision risk height. With eyes focused downwards, they search for telltale signs of fish. When a shoal is spotted, they rise to gain height, oblivious to the danger from blades, and plummet almost vertically into the water. On the other hand, a report published last year by the British Trust for Ornithology suggested that gannets tend to avoid wind farms. Nobody really knows how serious the risks are; victims’ carcasses are soon swept away by the sea.
As more wind installations are proposed, the gannet’s vulnerability is becoming an issue. Wind farms may even impinge on Scotland’s Bass Rock gannet colony, the world’s largest and the place which gave the species its Latin name, Morus bassanus. There is no easy way to find out what is going on but, in the current edition of Ringing & Migration, Robert Furness and Sarah Wanless suggest how the risks gannets face might be assessed. Our largest seabird is an impressive creature. The adult feathers are gleaming white, apart from those of the outer wings, which are black, and some yellow ones on the head. The species, once very scarce, has prospered over the last century-and-a-half. A few decades ago, we had just three breeding colonies off Ireland. Now we have six. These members of the pelican tribe wander far and wide. With rising sea temperatures, fish are moving northwards and seabirds seem to be following suit.
Gannets, however, take many kinds of fish and can travel long distances to catch them; they are less vulnerable to changes in fish distribution. At any rate, they are staying faithful to their traditional breeding locations. According to Furness and Wanless, this fidelity might help scientists estimate their mortality. By placing coloured rings on legs at colonies, and checking how many marked birds return in the spring, we can estimate annual death rates. Adult survival, according to Wanless, is 92% year-on-year while about 30% of chicks reach the age of four. Deaths will have many causes, by-catch in fishing nets and contamination by discarded oil among them. Casualty rates from collisions with turbine blades will be embedded in the overall figures and difficult to isolate. Furness and Wanless suggest that birds should be ringed systematically at key colonies close to wind farms and at locations well away from them. If mortality at the vulnerable colonies turns out to be significantly higher than elsewhere, it will indicate that gannets are at risk from turbines. However, only 172 gannets were ringed in Britain and Ireland in 2012 and 75 in 2013. Many more birds will have to be ringed if the proposed method of measuring mortality is to be reliable. Our Irish colonies might serve as a ‘control group’ for such a project.
Those at Little Skellig and Bull Rock are well away from wind farms. The Ireland’s Eye and Lambay ones, in the Irish Sea, are relatively close to wind installations, so their birds might be at risk, while the one at Great Saltee, off Wexford, is intermediary. Gannet ringing, however, is difficult, expensive and weather-dependent. Although using video and IT technology helps, even monitoring the return of ringed birds to a colony is a challenging and expensive. However, a study of gannet mortality here would be immensely valuable.