Protected populations of gannets are at a greater risk from offshore wind farms than previously thought because a new study has found that they fly at an average height of 27 metres above sea level when actively searching and diving for prey thereby increasing their chances of being hit by the blades of wind turbines.
The study carried out by researchers at Universities of Leeds, Exeter and Glasgow found that though the gannets may be flying at an average height of 22 metres above sea level when commuting or migrating, they fly above that height when searching for prey and this is what poses a huge risk for them.
Researchers also found that the birds’ feeding grounds overlap extensively with planned wind farm sites in the Firth of Forth, heightening their risk of colliding with turbine blades.
Up to 12 times more gannets could be killed because of wind turbine blade collisions than current figures suggest and though researchers have based their calculations using current typical turbine sizes, which could be different to those actually installed, there is great uncertainty over actual turbine avoidance rates.
The study, overseen by Professor Keith Hamer, of the School of Biology at Leeds, is based on the world’s largest colony of gannets with some 70,000 breeding pairs, situated in the Firth of Forth in south-east Scotland, less than 50 kilometres from several planned wind farm sites.
Hamer explains that their study sheds light on the methods being currently used to assess potential collision risks from offshore wind farms. As it stands, previous methods used to measure gannet flight heights were either done visually or through radars. Radars have been an expensive preposition with a limited range of about 6km and hence there have been instances were trained eyes were used more often to assess gannet flight heights.
Hamer and team recommend use of loggers that would allow for much more efficient and precise tracking in combination of existing data from radar studies or observers at sea.
Dr Ian Cleasby, of the University of Exeter and lead author of the study, points out that there have been serious underestimations when it comes to potential collisions and though there is a lot of uncertainty surrounding the actual number of gannet deaths because of turbine blade hits, if their predictions do happen to be true, the deaths would be high enough to cause concern over the potential long-term effects on population size.
“Our predictions suggest extra care be taken when designing and assessing new wind farms to reduce their impact on gannets”, Cleasby said.
“For the first time we’ve been able to track birds accurately in three dimensions as they fly from their nests through potential wind farm sites.” saud co-author Dr Ewan Wakefield, of the University of Glasgow. “Unfortunately, it seems that many gannets could fly at just the wrong heights in just the wrong places.”
“Increasing the distance between the tips of the spinning turbine blades and the sea would give gannets more headroom – so we strongly urge that the current minimum permitted clearance turbine height be raised from 22m to 30m above sea level.”
Using miniaturised light-weight GPS loggers and barometric pressure loggers, temporarily taped the birds’ tails, the researchers tracked the flights of gannets in three-dimensions as they flew out from the Bass Rock, searching for fish.
They then used the data in a predictive model which suggested that, based on available estimates of the proportion of birds that would be likely to avoid the turbine blades, about 1,500 breeding birds could be killed each year at the two planned wind farms nearest to the Bass Rock.
The study has been published in the Journal of Applied Ecology.
