Offshore wind farms which are to be built
in waters around the UK could pose a greater threat to protected populations
of gannets than previously thought, research led by the University of Leeds
says.
It was previously thought that gannets, which breed in the UK between April
and September each year, generally flew well below the minimum height of
22 metres above sea level swept by the blades of offshore wind turbines.
However, while this is the case when the birds are simply commuting between
their nest sites and distant feeding grounds, this new study shows that
they fly at an average height of 27 metres above sea level when actively
searching and diving for prey.
Crucially, the study also shows 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.
The researchers estimate that up to 12 times more gannets could be killed
by turbines than current figures suggest, although they stress that the
figure is based on calculations using current typical turbine sizes, which
could be different to those actually installed, and that there is great
uncertainty over actual turbine avoidance rates.
Previously data on gannet flight heights were obtained by one of two methods:
trained surveyors on boats estimating heights by eye, or radar, which usually
has a limited range of about 6km and is costly. The researchers conclude
that more sophisticated methods of assessing risk should be adopted urgently.
Professor Keith Hamer, of the School of Biology at Leeds, oversaw the study,
published today in the Journal of Applied Ecology. His research group,
together with colleagues from Exeter and Glasgow, based their work at Bass
Rock, 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.
"There’s a lot of
uncertainty over how many birds would actually be killed"
He said: “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.”
Dr Ian Cleasby, of the University of Exeter and lead author of the study,
said: “Previous data had seriously underestimated the number of birds
potentially at risk of colliding with turbine blades. 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.”
"we strongly urge that the current minimum permitted clearance turbine
height be raised from 22m to 30m above sea level"
Co-author Dr Ewan Wakefield, of the University
of Glasgow, 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.
“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 government expects offshore wind power could supply between eight and
10% of the UK’s annual electricity supply by 2020. It currently supplies
about 4%, according to the latest official figures.*
The study was funded by the Natural Environment Research Council and the
Department of Energy & Climate Change (DECC). A further, more extensive
tagging study to improve understanding of gannet flight heights and behaviour
has been funded by DECC in 2015. This work is being led by Professor
Hamer.