Bird death and wind turbines: a look at the evidence
- 10 Apr 2013, 16:30
- Robin Webster and Freya Roberts
The Royal Society for the Protection of Birds (RSPB) and
windfarm opponents have found themselves at odds over the risk
turbines pose to bird species, particularly birds of prey. Carbon
Brief examines what the peer-reviewed research says about turbines'
impacts on birds.
An article in last weekend's
Mail on Sunday claims wind farms are "destroying rare birds",
arguing turbines kill birds of prey including hen harriers and
golden eagles. And in another piece, the
Telegraph says a US-based conservation
group fears windfarms will "massacre" eagles.
But in a
response to the claims, the RSPB's conservation director,
Martin Harper, says a large body of scientific evidence shows
"appropriately located windfarms have negligible impacts" on bird
Why birds are affected
There are reasons why birds are likely to be affected by
windfarms. Wind developments tend to be placed in upland areas with
strong wind currents that have a lot of potential to generate
energy. Birds - particularly raptors like eagles or vultures - use
currents as highways - and so are likely to come into contact
with the turbines.
It's not just the turbine blades that pose a risk to birds;
research indicates that wind developments can
disrupt migration routes. What's more, foraging and nesting
habitat can also be lost when turbines are put up.
What's the impact on bird populations?
Despite these concerns, the current body of research suggests
windfarms have not significantly reduced bird populations.
suggest birds have the ability to detect wind turbines in time
and change their flight path early enough to avoid them. And one
small study found no evidence for sustained decline in two
upland bird species on a windfarm site after it had been operating
for three years. Another found that wild geese are
able to avoid offshore wind turbines.
large peer-reviewed study in the Journal of Ecology
monitored data for ten different bird species across 18 wind farm
sites in the UK. It found that two of them- curlew and snipe - saw
a drop in population during the construction phase, which did
not recover afterwards. But the population of the other
eight species were restored once the windfarms were built.
Wind turbines and birds of prey
Windfarms may not affect all birds, but what if they affect
birds of prey disproportionately? Some of the reason why this might
happen is genetic -
certain species like vultures, for example, have blind spots in
their visual field which mean they cannot see objects directly in
front of them (like wind turbines) when flying.
Large birds like hen harriers, eagles and vultures are also
slower to reproduce than other species and so their populations are
more likely to be affected by a small number of deaths.
There are specific locations elsewhere in the world where
windfarms have caused impressive-sounding numbers of fatalities
amongst birds of prey. In the
Altamont Pass in California, for example, one study found about
4,000 wind turbines killed 67 golden eagles and 1,127 birds of prey
in a year.
southern Spain, 252 wind turbines located in an area used by
many birds of prey and on the migratory path of many large birds
killed a 124 birds of prey in a year. At
another location in southern Spain 256 turbines killed 30
griffin vultures and 12 common kestrels.
The RSPB references these studies, concluding
"some poorly sited wind farms" in California and Spain have caused
major bird casualties - in other words the windfarms were sited in
areas where there were a lot of birds and not enough thought given
to what the effects will be on bird populations. But it adds that
these are atypical and a result of bad planning in sensitive areas
-arguing that better-sited windfarms do not cause the same
number of deaths.
Siting of wind farms
What evidence is the RSPB relying on? There are studies to show
that siting windfarms more sensitively can make a difference to how
bird populations adapt to their new neighbours. In one frequently
cited study, one
windfarm in Spain created feeding sites away from turbines and
shut down turbines at peak flight times. Vulture deaths were
reduced by 50 per cent for an electricity production loss of just
0.07 per cent.
The RSPB's parent group Birdlife
International describes another project in Wyoming. Windfarms
located on a flight path used by golden eagles and hawks posed a
"serious threat", it says. But the turbines were set back slightly
- with the result that ultimately very few birds are killed.
According to Birdlife
International, with a thorough environmental assessment as part
of the planning process, bird deaths can be significantly reduced.
In Scotland for example, planners
use maps to identify high risk areas for protected birds. Some
wind farms, such as the
Penescal windfarm in Texas, use radar systems to detect flocks
of birds and shut off the wind turbines as they approach.
Overall, the RSPB says it scrutinises "hundreds" of windfarm
applications every year in order to assess their possible impact on
wildlife and bird populations and ultimately objects to six per
cent of them.
A comparison of deaths - what else kills
Lots of human activities kill birds. What's perhaps surprising,
given the amount of attention it gets, is how few birds wind
turbines kill in relation to other things.
Several studies have compared the effect of different energy
sources on bird mortality overall. One,
published earlier this year, calculates windfarms killed 20,000
birds died in 2009 in the US - while nuclear plants killed about
330,000 and fossil fueled power plants more than 14 million. The
research concludes that taken together, fossil-fueled
facilities are about 17 times more dangerous per gigawatt hour of
electricity produced to birds than wind and nuclear power
And that's without getting into other human activities and
structures - including buildings, roads and domestic cats. US
estimates published last year in a
commentary piece in the journal Nature, although highly
uncertain, also suggest the impact of wind turbine is far smaller
than many other causes of bird death:
says it supports wind power - not because windfarms pose a lower
risk to birds than other energy sources - but because in its view
climate change poses the "single
greatest long-term threat" to bird species. Climate change is
predicted to harm bird populations by affecting
migration patterns, or altering their
There is evidence to show that in certain, specific locations
windfarms have caused significant fatalities amongst birds of prey
- but there doesn't seem to be any evidence supporting the
conclusion that birds of prey will be 'massacred' on a wider scale.
The few studies on windfarm siting are also encouraging, indicating
that it can be used as an effective tool to reduce mortality.
Compared to other aspects of modern society, careful planning can
lead to much-reduced mortality.