Stolen lives

Every year in France, tens of thousands of birds are mowed down in mid-flight by the blades of wind turbines. In view of this high mortality rate, and at a time when the French government is planning to double the number of wind farms, the MAPE program brings together private and public players to ensure that wind power doesn't blow these people away.

On the morning of January 16, a golden eagle was found dead at the foot of a wind turbine at the Bernagues site in the Hérault region(France 3, 27/01/2023). Avian mortality attributable to wind turbines is a phenomenon whose scale remains poorly understood, "the figure circulating is 7 deaths per year and per wind turbine in France. This figure is probably underestimated and, above all, does not distinguish between species; birds of prey, which need wind to move around, are in competition for space with wind turbines", explain Olivier Duriez and Aurélien Besnard, biologists at the Centre d'écologie fonctionnelle et évolutive in Montpellier* and scientific leaders of the MAPE project (Mortalité aviaire dans les parcs éoliens).

Launched in 2019 on the initiative of the Dreal Occitanie and the Ligue de protection des oiseaux (LPO) with the Maison des sciences de l'Homme, MAPE brings together a consortium of public and private players, including 25 wind power operators, to reduce this avian mortality. In response to societal expectations, more and more wind farms are equipping their turbines with automatic detection systems (ADS) that command the blades to stop when a bird approaches. " The first step was to provide operators with a scientific protocol for assessing the effectiveness of these systems, for which there are virtually no studies," explains Aurélien Besnard. Because even in a park equipped with an ADS, collisions continue to occur.

Theft detector

To better regulate these SDAs, the researchers have also developed EolDist. This free Internet application calculates the minimum distances required to detect a bird by cross-referencing, thanks to an integrated database, the speed and type of flight according to the species with meteorological data and the machine's stopping time. " If I take the golden eagle, which flies at an average speed of 15 metres per second, and the wind turbine takes 41 seconds to stop, our eagle will have to be detected at 875 metres to avoid a collision," explains Olivier Duriez. Although tests have been carried out, more are needed to improve the application's robustness, but operators are reluctant to carry them out. Eoldist's results tend to call into question the very logic of these detection systems," notes Aurélien Besnard. If wind turbines stop every time a bird passes 500 meters away, they will stop all the time, which is still the best way to avoid bird mortality, but is not economically viable.

At the same time, the researchers are also working on the effect of environmental conditions on the risk of collision: "Can fog, rain or wind encourage collisions? Does terrain play a role?" asks Olivier Duriez. They are exploring these avenues by analyzing collision videos filmed by wind turbine cameras. "Having operators in the consortium gives us access to these images, which are quite sensitive data for wind farms. The results could lead to better site selection for wind farms, as well as adapting their operation when weather conditions are favorable to collisions.

Plucked populations

Another aim of the MAPE program is to raise awareness of biodiversity issues by developing EolPop, a simple application for calculating the impact of mortality on a species' population dynamics. " Losing an eagle or a chickadee does not have the same consequences in terms of the long-term viability of the population," warns Olivier Duriez. EolPop enables its users, whether wind farm operators or nature conservation associations, to cross-reference survival and fecundity values for each species with population size data. " The approach we have chosen is to compare the population sizes we would have in 30 years' time, with or without the wind farm".

Let's take the golden eagle again: with one mortality per year for a population of ten pairs, the population becomes extinct in less than 30 years. Fortunately, not all species are affected to the same extent, but it does help us to be objective," continues the researcher. Today, some consultancies say that one eagle a year isn't much. But not much compared to what? Here, we have figures derived from robust calculations," adds Aurélien Besnard. Figures that shed a rather ominous light on other issues: France currently has 8,000 onshore wind turbines, and plans to double this number by 2028. Wind power has a future, the golden eagle less so.

*Cefe (CNRS, UM, IRD, EPHE, Inrae, Institut Agro, UPVM)