Offshore wind farms threaten northern gannets at Bass Rock

By Tracy Brighten

Northern gannets around the UK are at much greater risk from wind turbine blades than previously thought, according to new scientific research  

northern gannet

Several wind farms are due to be built in the next five years at locations within 50 kilometres of Bass Rock, the world’s largest gannet colony, located in the Firth of Forth off the east coast of Scotland.

The northern gannet is amber listed according to a UK national assessment of Birds of Conservation Concern. This new study, published in the Journal of Applied Ecology, highlights the urgent need for further research to inform wind turbine specifications and locations. 

Northern gannets were previously thought to fly well below the permitted minimum blade clearance height of 22 metres above sea level. This new study suggests that gannets fly below this height only when flying between breeding and feeding grounds. While hunting and diving for prey, these large seabirds with a wingspan of almost two metres were found to reach heights of 27 metres, placing them at risk of collision with rotating blades.

The findings suggest that collision risk has been seriously underestimated and up to 12 times more gannets could be killed than previously thought.

Previous collision risk estimates were based on flight height data from radar, limited to a range of six kilometres, as well as subjective ship-based observations. Estimates in this new study are based on more reliable data. Global Position System (GPS) loggers and barometric pressure loggers tracked the movements of gannets rearing chicks on Bass Rock from mid-June to mid-August over a three-year period.

“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,” said study co-author Dr Ewan Wakefield of the University of Glasgow Institute of Biodiversity.

Led by Professor Keith Hamer, of Leeds University’s School of Biology, researchers from Leeds, Glasgow and Exeter Universities tracked a study population of 55 breeding gannets. The birds were fitted with lightweight GPS loggers, and a subset of birds fitted with a barometric pressure logger to more accurately measure height. Loggers were attached to the bird’s tail feathers.

Researchers found that when travelling between the colony and foraging sites, gannets flew at a median height of 12 m, but when actively foraging, the median height was 27 m. Eleven of the sixteen birds fitted with altitude loggers were tracked at these heights within the proposed location of two wind farms in the Firth of Forth. Foraging range was found to extend up to 536 km from Bass Rock, home to around 70,000 breeding gannet pairs.

Assuming similar foraging in the incubation as the chick-rearing study period, the research team estimate a mortality rate of 1500 breeding gannets from the Bass Rock colony during April to September each year as a result of birds colliding with turbines at the two planned wind farm sites.

This estimate assumes a minimum blade clearance height of 30 m, 8 m above the current permitted minimum, and it does not include juveniles, non-breeding birds, or account for Bass Rock breeding birds that may be killed at other wind farms during their 3-month absence from the colony. Bird population size, sex, weather and prey availability also affect foraging behaviour. This study was carried out in summer in relatively calm conditions with average prey availability.

A large increase in offshore wind turbine capacity is anticipated within the next decade, prompting serious concerns about collision risk. The UK government expects wind power to account for 8% to 10% of the UK annual electricity supply by 2020, up from the current 4%.

The research team recommends raising the minimum permitted clearance height of turbine blades from 22 m to 30 m above sea level at sites with high collision risk for foraging gannets. Further research data from GPS and barometric pressure loggers is also needed to make a proper assessment of the risk of offshore wind farms to gannets and other vulnerable bird populations.

“Our predictions suggest extra care be taken when designing and assessing new wind farms to reduce their impact on gannets,” said University of Exeter’s Dr Ian Cleasby, lead author of the study. 

Image credit:
Bass Rock by Threefishsleeping on Flickr (CC BY-ND 2.0)
Gannets at Bass Rock by Robert Orr on Flickr (CC BY-ND 2.0)