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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 populations.  

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 these 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.

Several studies 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.

A 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.

In 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 birds?

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 stations.

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:

Nature Image

The RSPB 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 breeding or migration patterns, or altering their habitats.

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.

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