Monitoring bird mortality at operational wind farms

Monitoring bird mortality at operational wind farms

One of the most significant environmental risks relating to wind power is the mortality of birds and bats resulting from operational wind farms.

The causes for this mortality include direct collision with wind turbine blades, lung damage due to rapid changes in air pressure surrounding moving turbine blades (pulmonary barotrauma, a concern for bats in particular), electrocution on nearby power lines, habitat alteration, and displacement of migration routes. While the latter two causes present obvious challenges in quantifying mortality rates, deaths resulting from collision, barotrauma, and electrocution should theoretically be easy to estimate by counting avifauna carcasses in the area surrounding wind turbines and transmission lines. However, there are a number of variables in play to be considered when establishing a monitoring protocol, one of which is monitoring frequency.

The International Finance Corporation (IFC) / World Bank Group (WBG) does not set specific requirements for bird carcass monitoring frequency in their Environmental, Health, and Safety Guidelines for Wind Energy (2015). Rather, they specify that post-construction carcass searches “should be conducted for a minimum of one to three years subsequent to the initiation of wind farm operation,” and recommend that certain scientific design elements be incorporated into searches and evaluation, namely: correction for searcher efficiency bias; correction for carcass removal by scavengers; correction for unsearched areas; selection of carcass search frequency based on expected fatality and scavenging rates; selection of subsample of turbines to be searched; and selection of search area size and configuration.

One challenge associated with determining several of these design elements, however, is that scavenging rates often go underestimated. In a study undertaken by Farfán et. al, a total of 57 bird carcasses (22 pigeons and 25 quails) were placed around 2 wind farms in the Malaga province of southern Spain. Within 3 days, 100% of quail carcasses and 10% of pigeons had disappeared completely, with an additional 35% of total pigeons disappearing by day 14. Through their results, as well as those of their peers in separate studies, Farfán et. al concluded that the disappearance rate due to scavengers was much higher than the search intervals often suggested by environmental authorities of 7-14 days, that the total number of birds and bats killed by wind farms was clearly underestimated, and that it was reasonable to recommend a searching frequency of daily for small birds and 3-day intervals for medium-sized birds (2017). Unfortunately, resource constraints mean that it is not always realistic to implement monitoring intervals of this frequency on wind farm projects around the world.

One approach to address this problem is to employ and train members of the local communities in carcass searches. This approach has been successfully implemented in Jordan. An alternative approach is to develop formulae for estimating real mortality estimates based on a limited number of searches. One of the more effective methodologies for this task was published in a study by our colleague Alexis Puente Monteil. In his study, he establishes a model to estimate a mortality value that was found to be within the range of +/- 30% of the real value in 36 out of 42 (86%) of unbiased scenarios, based on detailed and complete mortality data sets (2017). The full publication and formula are referenced below.

Despite the difficulties encountered in establishing the most effective monitoring frequencies to estimate true mortality, it is encouraging to see the progress which has been made through the involvement of local communities and the reliable extrapolation using limited data. As the field of wind energy continues to evolve, we can hope to observe continued advancement in the accuracy of these estimates, as well as in the effective mitigation of avifaunal mortality and conservation of biodiversity that we are ultimately trying to achieve.


Farfán, M.A., Duarte, J., Fa, J.E., Real, R., and Vargas, J.M. (2017). Testing for errors in estimating bird mortality rates at wind farms and power lines. Birdlife Conservation International. 27:431-439.doi:10.1017/S0959270916000460.
Puente Montiel, A. (2017). Critical Review of the wildlife monitoring protocol in wind farms: state of the art and proposals for improvement. Retrieved from

World Bank Group. (2015, August 7). Environmental, Health, and Safety Guidelines for Wind Energy.Retrieved from

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