# Wind farms and griffon vultures: no evidence for habituation and coexistence, a reply to Farfàn et al.

Olivier Duriez, Alvaro Camiña-Cardenal, Yohan Sassi, Constance Blary, Thierry Chambert, Cyrielle Ballester, Aurélien Besnard, Alexandre Millon

► To cite this version:

Olivier Duriez, Alvaro Camiña-Cardenal, Yohan Sassi, Constance Blary, Thierry Chambert, et al. Wind farms and griffon vultures: no evidence for habituation and coexistence, a reply to Farfàn et al. Global Ecology and Conservation, 2024, 51, pp.e02921. 10.1016/j.gecco.2024.e02921. hal-04593831

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# Wind farms and griffon vultures: No evidence for habituation and coexistence, a reply to Farfán et al.

## ARTICLE INFO

### Keywords

Bird abundance

Conservation

Environmental impact

Gyps fulvus

Renewable energy

Before-After-Control-Impact

## ABSTRACT

In a recent paper, Farfán et al. (2023) suggested that a population of griffon vultures in Málaga province (southern Spain) have gradually become habituated to the presence of wind turbines, and even actively avoid them, thus reducing the risk of collision. We believe, however, that their general conclusion that vultures have left the study area of impact immediately after construction of the windfarm, and have gradually recolonized the area, while avoiding collisions by passing alongside or above the wind turbines, is not supported by the results presented. Below we raise three key points explaining why the conclusions of Farfán et al. (2023) are flawed.

The development of wind energy production, as a response to the challenges imposed by global climate change, poses increasing threats to biodiversity, and to flying animals in particular (Katzner et al., 2019). Among birds, the griffon vulture *Gyps fulvus* appears as particularly at risk of collision with wind turbines, due to its flight characteristics (i.e. a large soaring bird flying extensively at rotor's height; Thaxter et al., 2017). In Spain only, it is estimated that several hundreds of individuals died of collision annually over the last decade (de Lucas et al., 2012; Morant et al., 2024; Sebastián-González et al., 2018). Besides mitigation measures to attempt reducing mortalities by collision, such as the onset of automatic detection systems (McClure et al., 2018), or shut-down on demand (Ferrer et al., 2022), it is supposed that some species may progressively adapt to these new artificial infrastructures occupying the airspace. In a recent paper, Farfán et al. (2023) suggested that a population of griffon vultures in Málaga province (southern Spain) have gradually become habituated to the presence of wind turbines, and even actively avoid them, thus reducing the risk of collision. We believe, however, that their general conclusion that vultures have left the study area of impact immediately after construction of the wind energy facility (hereafter WEF, synonym to wind farm but with more emphasis on the industrial rather than agriculture context), and have gradually recolonized the area, while avoiding collisions by passing alongside or above the wind turbines, is not supported by the results presented. Below we raise three key points explaining why the conclusions of Farfán et al. (2023) are flawed.

First, the study design is not suited to properly demonstrating a habituation to WEFs by vultures. Answering this question requires a Before After Control Impact (BACI) study design: multiple experimental sites (ones affected by WEF), compared to multiple control sites (similar topographical and environmental conditions but without WEF), with bird abundance and behaviour measured accurately during a similar period of time before and after the deployment of wind turbines. Although we recognise that such a study design is difficult to obtain in a WEF context, it is not impossible. For instance, Barrientos et al. (2012) demonstrated the effect of wire marking of power lines to reduce bird mortality, using a BACI study design. As acknowledged by Farfán et al. (2023) in the discussion, there was no (spatial) control site and no replication (neither control nor experimental sites). Regarding the temporal (before – after) control, the authors reported first a decrease in vulture abundance in the years immediately after construction (2005–2006) and later a small increase in 2010–2011 and a larger increase in 2018. The first decrease is not supported by any data, since there were no counts available with a similar protocol reported before the construction, but only the mention of 0.9 raptor/hour (including 10.7% that were griffons) recorded in 2001. To demonstrate such a decrease, the authors should have explicitly indicated the abundance of griffon vultures (not only raptors) prior to construction, and explain how this abundance was recorded (sampling effort and protocol). Figure 2 actually does not show any vulture observations in 2001 despite a mention in the text. Furthermore, the late increase in vulture abundance around the WEF, interpreted by the authors as the habituation of vultures to the WEF, can have alternative explanations. The last national census of griffon vultures in Spain (Del Moral and Molina, 2018) showed a 6% annual increase in griffon vulture populations in the Malaga province, resulting in 69% increase between 2009 and 2018 censuses. Thus, the most parsimonious hypothesis to explain the observed increase in vulture abundance at the focal WEF is that it is a consequence of the general growth of
griffon vulture population in the region. The behavioural habituation of vultures to WEF cannot be inferred without proper control sites (Conkling et al., 2021).

Second, both fatality searches and vulture observations surveys at the WEF site suffer from small sample size and low data quality. Regarding the carcass survey, the authors described a searching effort totalling only 73 hours, with a strong reduction in effort over time: from 38 h in period 1 (six months duration), 25 h in period 2 (six months duration), to only 10 hours in period 3 (three months duration in 2018). For 16 turbines (before 2009) and 18 turbines thereafter, and considering weekly searches as written in the methods, a simple calculation gives that each turbine has been surveyed for no more than 5.9 min in Period 1, 3.5 min in each period 2 and 3 min in period 3. Such a timing cannot allow a careful search over the entire wind facility area, totalling 277,089 m², considering a 70 m radius around each turbine as stated in the methods (IFC-EBRD-KfW, 2023). In addition, to account for carcass persistence rate, the authors refer to another study (Farfan et al., 2017) where they studied the scavenger activity using carcasses of pigeons and quails in two other WEFs, potentially holding different vegetation cover and scavenger communities. Given the very low, and decreasing fatality search effort (resulting in low precision of estimates, and likely causing an increasing bias of this estimate over time), and the uncertainty regarding carcass persistence rate, no conclusion can be drawn from the fatality searches.

Third, the whole study relies on only 120 h of vulture flight observations, during three periods of 3-months, interspaced by four to seven years: 48 h in 2005–2006, 48 h in 2010–2011 and 24 h in 2018. Furthermore, the sampling time was performed on a weekly basis from 9:00–11:00 UTC. However in spring in Spain, griffon vultures rarely start flying before 10:00 UTC. waiting for suitable conditions for soaring flight (i.e. the onset of thermal uplifts; Arrondo et al., 2021). Given the distance of 15 km between the WEF and known breeding colonies and roosts in the area, most vultures may probably not have arrived to the WEF before 11:00 UTC. Therefore, we consider that censuses have been performed outside the peak of flight activity of vultures at this period. These two methodological aspects (small sample size of observation time and early morning observations) may explain the very few numbers of vulture flights recorded. Finally, the quality of data may be questionable, since all vulture tracks were recorded by two observers, only equipped with binoculars, from one single central vantage point. It is well known that humans are poor at judging distances beyond several hundred meters, and even worse for judging distance and height (i.e. above ground level) of flying objects (Dokter et al., 2013; Mateos et al., 2010; McClure et al., 2018; Nolte et al., 2016; Williams et al., 2007). Because of the perspective from a single observation point aligned with the turbine rows, with the furthest turbine located >1 km from the observers, the exact distinction and quantification of “internal” and “external” flight paths relative to the wind turbines should be prone to errors, without the use of laser range-finder or radar.

Based on the methodological issues we have raised above, we believe that the general conclusion of vultures habituating to wind turbines cannot be drawn from the data presented by Farfan et al. (2023). Furthermore, the statement of “habituation” may only hold for a fraction of local breeding vultures, since the study focuses in spring months (during the breeding season) and does not account for large number of immature griffon vultures in migration or erraticism stage that cross each year in the study area in the autumn months (CSMAEA, 2023), increasing the likelihood of collision, as shown by De Lucas et al. (2012). Finally, the word “habituation” itself is problematic, because testing for the occurrence of habituation *sensu stricto* would require to record behavioural changes at the individual level, e.g. from GPS-tracked individuals before and after the WEF installation. The danger behind drawing such conclusions unsupported by data is that one could be tempted to extrapolate the current results to other sites and to implement WEF’s closer to vulture colonies. Given the high vulnerability to collisions of large soaring birds such as griffon vultures, and given the endangered status of vultures worldwide (Buechley and Sekercioglu, 2016; McClure et al., 2023), we think this should be avoided at all cost.

### CRediT authorship contribution statement

**Alvaro Camiña-Cardenal:** Writing – review & editing, Writing – original draft, Methodology. **Yohan Sassi:** Writing – review & editing, Writing – original draft. **Constance Blary:** Writing – review & editing, Writing – original draft. **Thierry Chambert:** Writing – review & editing, Writing – original draft. **Cyrielle Ballester:** Writing – review & editing. **Aurélien Besnard:** Writing – review & editing, Writing – original draft, Conceptualization. **Alexandre Millon:** Writing – review & editing, Writing – original draft, Conceptualization. **Olivier Duriez:** Writing – review & editing, Writing – original draft, Supervision, Conceptualization.

### Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Data Availability

No data was used for the research described in the article.

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Olivier Duriez<fnref n="1" />,<fnref n="1" />

CEFE, Univ Montpellier, CNRS, EPHE, IRD, 1919 route de Mende, Montpellier 34293, France

Alvaro Camiña-Cardenal<fnref n="2" />

ACRENASL Env. Consultants Ltd., Apartado de Correos 339, Majadahonda 20220, Spain
E-mail address: acamia@acrenasl.eu.

Yohan Sassi<fnref n="3" />, Constance Blary<fnref n="4" />

CEFE, Univ Montpellier, CNRS, EPHE, IRD, 1919 route de Mende, Montpellier 34293, France
E-mail addresses: yohan.sassi@cefe.cnrs.fr (Y. Sassi), constance.clary@cefe.cnrs.fr (C. Blary).

Thierry Chambert<fnref n="5" />

ACRENASL Env. Consultants Ltd., Apartado de Correos 339, Majadahonda 20220, Spain
E-mail address: thierry.chambert@cefe.cnrs.fr.

Cyrielle Ballester<fnref n="6" />

CEFE, Univ Montpellier, CNRS, EPHE, IRD, 1919 route de Mende, Montpellier 34293, France
E-mail address: cyrielle.ballester@cefe.cnrs.fr.

Aurélien Besnard<fnref n="7" />

CEFE, Univ Montpellier, CNRS, EPHE-PSL University, IRD, 1919 route de Mende, Montpellier 34293, France
E-mail address: aurelien.besnard@cefe.cnrs.fr.

<footnote n="1">¹ https://orcid.org/0000-0003-1868-9750</footnote>

<footnote n="2">² https://orcid.org/0000-0001-6414-5856</footnote>

<footnote n="3">³ https://orcid.org/0000-0002-1551-4421</footnote>

<footnote n="4">⁴ https://orcid.org/0000-0001-6204-9983</footnote>

<footnote n="5">⁵ https://orcid.org/0000-0002-9450-9080</footnote>

<footnote n="6">⁶ https://orcid.org/0009-0007-3504-4408</footnote>

<footnote n="7">⁷ https://orcid.org/0000-0002-2289-9761</footnote>

<footnote n="8">⁸ https://orcid.org/0000-0002-9475-4123</footnote>
Alexandre Millon<sup>8</sup>

Aix Marseille Univ, Avignon Univ, CNRS, IRD, Institut Méditerranéen de Biodiversité et d'Ecologie, Technopôle Arbois-Méditerranée, Aix-en-Provence, France

E-mail address: alexandre.millon@imbe.fr.

* Corresponding author

E-mail address: olivier.duriez@cefe.cnrs.fr (O. Duriez).

<footnote n="1">¹ https://orcid.org/0000-0003-1868-9750</footnote>

<footnote n="2">² https://orcid.org/0000-0001-6414-5856</footnote>

<footnote n="3">³ https://orcid.org/0000-0002-1551-4421</footnote>

<footnote n="4">⁴ https://orcid.org/0000-0001-6204-9983</footnote>

<footnote n="5">⁵ https://orcid.org/0000-0002-9450-9080</footnote>

<footnote n="6">⁶ https://orcid.org/0009-0007-3504-4408</footnote>

<footnote n="7">⁷ https://orcid.org/0000-0002-2289-9761</footnote>

<footnote n="8">⁸ https://orcid.org/0000-0002-9475-4123</footnote>