19 April 2012
Wind farms: new perspective needed to assess risks to birds
Risk assessments of potential bird mortality caused by planned wind farms should be
assessed at the scale of the individual turbine rather than the whole farm, according to new
research. It indicated that risk assessments made prior to building are not predicting the
actual level of mortality when the farm is built.
Although most recorded collision rates of birds at wind farms are low, some poorly sited farms have caused
higher mortality rates. In an attempt to prevent this, environmental authorities conduct environmental impact
assessments (EIA) of proposed wind projects, which cover likely effects to the site’s bird population. These EIAs
are conducted at the scale of the wind farm.
This study analysed the relationship between the risk prediction according to EIAs, and the actual recorded
mortality of the birds for wind farms in Southern Spain after they became operational. Twenty wind farms
(consisting of 252 turbines) were investigated in Andalusia, Spain near the Strait of Gibraltar, an important bird
migration route. The EIAs for these wind farms included risk assessments of bird mortality from collision, which was
calculated using two indices, both of which assumed that mortality risk is strongly dependent on abundance of
The proposed wind farm locations were classified into three risk levels (1, 2 or 3) with 1 representing lowest risk
and 3 representing highest risk. Most of the farms that finally obtained permission were at risk level 1, although
some had a risk level of 2. Between 2005 and 2008, when the farms were operational, the actual bird mortality
caused by collision with turbines was monitored on a daily basis. Using these data, the study calculated two
mortality rates: total bird mortality across all species and mortality for just raptor (bird of prey) species.
The researchers conducted daily surveys of the number of dead birds found in the close vicinity of the turbines
between 2005 and 2008. 596 dead birds were found in total for all the wind farms. Taking into account the amount
of time the wind farms were operational (between 11 and 34 months), the (mean) average number of bird
mortalities per turbine per year was estimated to be 1.33. This is one of the highest mean collision rates reported
for all bird species. There were 214 raptor mortalities (36% of total mortality), the majority of which were griffon
vultures (138 birds, 23% of total mortality).
This study found no significant relationship between EIA risk indices calculated and the actual recorded bird
mortality when the turbine became operational. There was also no clear relationship between abundance of birds,
in terms of observed birds per hour and bird collisions per turbine per year. The lack of a clear relationship could be
partly due to gaps in data. Nonetheless, the study suggests it is too simplistic to assume a clear relationship
between frequency of birds and mortality, and that the individual species and topography of the individual turbine
should also be considered in EIA studies.
EIAs assess risk on the basis of local abundance of birds, but previous research has found that the probability of
bird collisions with turbines also depends on species behaviour and wind currents, which are affected by
topography and landscape. This suggests that environmental authorities may be using inadequate criteria to
assess potential risk of wind farms to birds and there may be a need for a new or modified tool, conducted at the
level of individual turbines.
Source: Ferrer, M., de Lucas, M., Janss, G.F.E. et al. (2012) Weak relationship between risk assessment studies and recorded mortality in wind
farms. Journal of Applied Ecology. 49:38-46.
Theme(s): Biodiversity, Climate change and energy, Risk assessment
The contents and views included in Science for Environment Policy are based on independent, peer-reviewed research and do not necessarily reflect
the position of the European Commission.
To cite this article/service: "Science for Environment Policy": European Commission DG Environment News Alert Service, edited by
SCU, The University of the West of England, Bristol.
European Commission DG ENV
News Alert Issue 280
19 April 2012