Offshore wind farm developments proposed for waters surrounding the United Kingdom could pose a higher risk to protected gannet populations than scientists previously thought, according to the findings of a study recently conducted by a team of researchers from Exeter, Leeds and Glasgow universities.
During the breeding season (between April and September) gannets conduct regular flights between breeding and feeding grounds in search of food to feed their young. While scientists initially believed that gannets typically flew well below 22 metres above sea level — the minimum height restriction for offshore wind turbine blades — they have since discovered that this only applies when the birds are commuting between nesting and feeding grounds, and in fact on average fly at a height of around 27 metres above sea level during feeding activities (i.e. while searching or diving for fish).
More importantly, the study shows that there is extensive overlap between the gannets’ feeding grounds and proposed wind farm sites in the Firth of Forth, greatly increasing the risk of collisions with wind turbine blades. The scientists estimate that gannet deaths due to collisions with turbines could in fact be as much as 12 times higher than current predictions suggest, depending on various factors. For example these figures are based on average wind turbine sizes currently in use, which may differ from those of turbines actually installed at the proposed developments; and there is also a great deal of uncertainty regarding actual wind turbine avoidance rates.
Previous studies that collected gannet flight data were conducted by either boat-based observations where observers estimated flight heights by eye; or flight data was gathered using radar, which typically has a range limit of around 6km and is expensive to conduct. The scientists recommend that more advanced methods of assessing the risk to gannets should be adopted as a matter of urgency.
The study was conducted at the world’s largest gannet colony, consisting of 70,000 breeding pairs of gannets, situated at Bass Rock in the Firth of Forth, to the south-east of Scotland — within 50 kms of several proposed wind farm development sites.
The researchers tracked the flight paths of gannets as they flew from their nesting sites at Bass Rock to their foraging groundings by attaching miniature light-weight data loggers that included an onboard GPS and barometric pressure logger to the birds. After inputting the data into a predictive model, they found that based on current estimates of the number of birds that would actively avoid turbine blades, around 1500 breeding gannets could be killed every year at two of the proposed wind farm developments closest to Bass Rock.
According to co-author, Professor Keith Hamer, from the School of Biology at Leeds University: “Our study highlights the shortfalls in current methods widely used to assess potential collision risks from offshore wind farms, and we recommend much greater use of loggers carried by birds to complement existing data from radar studies or observers at sea.”
“Previous data had seriously underestimated the number of birds potentially at risk of colliding with turbine blades,” said lead author, Dr Ian Cleasby, of the University of Exeter. “There’s a lot of uncertainty over how many birds would actually be killed this way, but our predictions – if realised in the field – are 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.”
“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,” explained 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.”
The UK government anticipates that by 2020 between 8-10% of the UK’s annual electricity will be supplied by offshore wind energy, which is currently producing around 4% of the nation’s annual electricity supply. It is critical that measures are implemented to ensure that growth in this sector does not incur a higher risk to avian populations.