Operations & Maintenance

Recent data indicates that wind turbines account for just one out of every 10,000 bird deaths. So why does potential bird strike continue to threaten major wind developments, and how can developers avoid this potential show stopper?

By Jason Deign

Do you have a killer on your wind farm? If so, it shouldn’t be hard to spot: its victims will literally be falling out of the sky.

‘Killer’ is a term used SEO/Birdlife conservation area technician Octavio Infante to describe the small number of turbines that contribute the most, annually, to a significant death toll among birds and bats. “Not all turbines have the same impact,” he notes.

If a turbine is sited on a migration path, however, or on a route used by birds or bats between roosts and feeding sites, it can become a serious cause of wildlife mortality. Moving at speeds in the order of 90 metres a second, rotor tips knock birds out of the air before they can react.

Bats appear to have even greater trouble with turbines, even though they use echolocation that, in theory, can help them avoid fast-moving objects. Infante says experts believe the sound and pale colour of rotors may attract insects at night, which increases the chances of bat strikes.

However, organisations such as the Centre for Sustainable Energy or the American Wind Energy Association note that some of the concern over bird and bat deaths in modern wind farms may be overblown.

Reports published by both bodies indicate that while turbine bird and bat kills can and do occur anywhere, two wind farm developments in particular have given the industry a bad reputation in this respect.

In the US, the California Altamont Pass Wind Resource Area has been blamed for the cull of six species of raptor and continues to record a high level of fatalities.

And in Spain, two installations in the Campo de Gibraltar mountains have affected bird populations; 63% of the raptor fatalities recorded are of griffon vultures, a protected species.

Older designs

In both cases the turbines involved were older designs which are thought to be harder for birds to avoid, and were sited on obvious avian flight paths. But their impact on the industry has been significant.

RenewableUK head of communications Nick Medic points out that bird strikes are now frequently cited as a reason for rejecting wind power planning applications.

“Sometimes you can have an opposition group starting a debate about a wind farm on a visual impact basis, but because it’s not enough to prevent it going ahead they would pile on the issue of bird strikes,” he says.

Such scaremongering is rarely based on fact, he adds. A survey of peer-reviewed data carried out by the Centre for Sustainable Energy indicates that wind turbines may account for just one out of every 10,000 bird deaths attributable to human action.

Even allowing for the fact that bird strikes may be under-reported (Infante points out that many dead birds could be taken by scavengers before they are found), this level is virtually insignificant compared to mortality from buildings, power lines or cats.

And that is before any comparison of wind power with the effects of global warming from non-renewable energy, which probably explains why established environmental campaign groups tend to take a relatively balanced view towards bird strikes.

Although SEO/Birdlife has halted the construction of a wind farm in Omaña, Leon, because of its potential impact on a Capercaillie nesting ground, “we are not against wind energy,” Infante says.

Runaway warming

Marie Reynolds, a spokesperson for Friends of the Earth, adds: “Fossil fuels are pushing our planet to the brink of runaway warming and if we don’t invest in green energy now, future generations will be landed with a bill that will dwarf the current financial crisis.

“We need to ensure wind turbines are carefully sited to reduce the already minimal impact on bird populations.”

So the message for wind farm operators is that they need to do their homework before selecting a site. Infante recommends a year-long environmental audit, to cover all migrant species and observe which areas birds or bats use for migrating and breeding.

And for established wind farms with an ongoing bird strike problem, there are a number of remedies. Infante says operators in the south of Spain now routinely keep a watch for migrating flocks and switch off turbines in their vicinity.

Even better, a Spanish company called Liquen is commercialising a system called DTBird, which detects birds in flight and sends a signal to switch off a turbine if a bird approaches within a given distance.

Such measures may seem over the top for cost-conscious wind farm operators, particularly when far more birds get killed every year by windows, pets and cars. But they are worth it if the industry wants to remain on the right side of public opinion.

“We hope the Omaña case will help wind power promoters to see the value of doing a thorough environmental assessment,” Infante says. “If they had chosen a different location those turbines would be working by now.”

To respond to this article, please write to the editor: Rikki Stancich