Wind Turbine Fatalities Approach a Level of Concern in a Raptor Population
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G Model JNC-25300; No. of Pages 7 ARTICLE IN PRESS Journal for Nature Conservation xxx (2013) xxx–xxx Contents lists available at ScienceDirect Journal for Nature Conservation jou rnal homepage: www.elsevier.de/jnc Wind turbine fatalities approach a level of concern in a raptor population a,∗ b c d J. Bellebaum , F. Korner-Nievergelt , T. Dürr , U. Mammen a Wiesenstr. 9, D-16278 Angermünde, Germany b Oikostat GmbH, Ausserdorf 43, CH-6218 Ettiswil, Switzerland c Landesamt für Umwelt, Gesundheit und Verbraucherschutz Brandenburg, Staatliche Vogelschutzwarte, Buckower Dorfstraße 34, D-14715 Nennhausen OT Buckow, Germany d ÖKOTOP Büro für angewandte Landschaftsökologie, Philipp-Müller-Straße 44/1, D-06110 Halle, Germany a r a t i b s c l e i n f o t r a c t Article history: Mortality from collisions with increasing numbers of wind turbines is a potential hazard to raptor popu- Received 15 October 2012 lations, but the actual effects on a population scale have rarely been studied based on field data. We Received in revised form 15 June 2013 estimated annual collision numbers for Red Kites Milvus milvus in the German federal state of Branden- Accepted 15 June 2013 2 burg (29,483 km ). A hierarchical model considering carcass persistence rate, searcher efficiency and the probability that a killed animal falls into a searched area was applied to results of carcass searches at 617 Keywords: turbines. Collision risk varied significantly with season. The model estimated 308 (95% CrI 159–488) Red Milvus milvus Kite fatalities at 3044 turbines operating during 2012, representing 3.1% of the estimated post-breeding Wind energy population of 9972 individuals. Using the potential biological removal (PBR) method, mortality thresh- Collision risk olds of 4.0% were obtained for migratory Red Kite populations. This level of mortality may be reached Carcass searches Potential biological removal when turbine numbers increase within a few years. Since wind turbine collisions may affect Red Kites throughout the global range, a more detailed assessment of the actual impacts on populations is needed, especially because the PBR does not account for the predominance of adult birds among the collision victims. © 2013 Elsevier GmbH. All rights reserved. Introduction range (e.g., Tellería 2009), large scale population effects may be suspected. At this scale, however, the cumulative total numbers The use of wind turbines to generate renewable energy has of fatalities at multiple wind farms are poorly known. Field stud- rapidly increased in the Northern Hemisphere during the last 15 ies are usually restricted to local or regional populations (Carrete years (Pullen & Sawyer 2011). The resulting increase in the number et al. 2012; Dahl et al. 2012). Studies assessing impacts on larger of wind farms has raised concern about their potentially nega- populations therefore used collision risk models instead of mortal- tive, cumulative effects on bird populations (Drewitt & Langston ity estimates from field data (Carrete et al. 2009; Eichhorn et al. 2006), but empirical evidence is scarce. Raptors Accipitriformes are 2012; Schaub 2012). regarded as particularly vulnerable, either to displacement from The Red Kite Milvus milvus is an endemic raptor species habitats, or to increased mortality due to collisions at turbines widespread across temperate and southern Europe. Regional popu- (Madders & Whitfield 2006). The two processes of displacement lations are declining in most of its breeding range and the species and collision are to some extent mutually exclusive, since birds is regarded as “near threatened” (Knott et al. 2009). In addition to avoiding the need to approach a wind farm would not collide with direct killing, accidental poisoning and electrocution, high num- the turbines. Collision mortality occurs in various raptor species bers of reported fatalities at wind turbines have recently been and throughout the annual cycle (Barrios & Rodriguez 2004; Dahl identified as a major source of additional mortality (Knott et al. et al. 2012; Smallwood & Thelander 2008), hence it is probably the 2009; Langgemach et al. 2010). Red Kites search for prey in open greater risk for many species. Raptors are long-lived species with landscapes. Especially in summer, when crops become too tall relatively low reproductive rates, and their populations may be and dense for foraging, they may be attracted to wind farms by especially sensitive to increases in adult mortality (Saether & Bakke favourable hunting conditions around the tower. Because most 2000). Where wind farms occupy large parts of a species’ breeding search flights are performed at rotor height they are especially vulnerable to collisions at wind turbines (Mammen et al. 2011). Environmental impact assessments in most countries focus on ∗ the potential effects of a single wind farm (Ferrer et al. 2012). Corresponding author. Tel.: +49 3331 296517. Because collision risk with each turbine is small, such assessments E-mail addresses: [email protected] will usually fail to predict negative effects on a population scale. (J. Bellebaum), [email protected] (F. Korner-Nievergelt), [email protected] (T. Dürr), [email protected] (U. Mammen). Models predict negative effects on populations if large numbers 1617-1381/$ – see front matter © 2013 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.jnc.2013.06.001 Please cite this article in press as: Bellebaum, J., et al. Wind turbine fatalities approach a level of concern in a raptor population. Journal for Nature Conservation (2013), http://dx.doi.org/10.1016/j.jnc.2013.06.001 G Model JNC-25300; No. of Pages 7 ARTICLE IN PRESS 2 J. Bellebaum et al. / Journal for Nature Conservation xxx (2013) xxx–xxx Table 1 Collision model Post-breeding population structure under a stable age distribution, given as propor- tion of the total population. To estimate collision rate, i.e., the monthly number of Red Kite Age Annual Breeding Proportion of Proportion of breeding fatalities per wind turbine, we used a hierarchical model similar survival a probabilityb individuals individuals to the model used by Korner-Nievergelt et al. (2013). Our model 0 0.60 0 0.30 0 consists of two sub-models, one for the collision process and one 1 0.74 0 0.19 0 for the search process. 2 0.84 0.20 0.13 0.03 In the search process sub-model, we assumed the number of 3 0.84 0.60 0.09 0.05 carcasses found per month and wind farm to be binomially dis- 4 0.88 0.80 0.06 0.05 ∼ 5 0.90 0.98 0.23 0.23 tributed, Yi binomial(Ni, pi), with Ni equalling the number of Red Total 1.00 0.36 Kites killed during month i and pi being the probability that a Red a Schönfeld (1984), Nachtigall (2008). Kite killed is later found by a searcher, henceforth called detection b Values chosen after Newton et al. (1989) and Nachtigall (2008). probability. To estimate detection probability, we laid out a total of 20 Com- mon Buzzards Buteo buteo as a surrogate for Red Kites at four of of wind farms are placed in Red Kite home ranges (Eichhorn et al. the wind farms studied. From repeated visits by different persons 2012; Schaub 2012), but these effects have not yet been demon- at intervals of 1–7 days until 15–30 days after placement, persis- strated for real populations. Here, we use results from carcass tence probability s and searcher efficiency f were estimated with searches in the German federal state of Brandenburg to estimate the a Cormack–Jolly–Seber model in MARK (White & Burnham 1999). cumulative total number of Red Kite collisions with all wind farms The estimates and 95% confidence intervals were transformed into s s f f in the study area. In order to assess their impact on the population Beta distributions, Beta(a , b ), and Beta(a , b ), respectively. We we compare the results with mortality thresholds. combined the average interval between the searches d, estimated carcass persistence probability s, and searcher efficiency f using the method of Korner-Nievergelt et al. (2011), to obtain the probabil- Methods ity p100 that a Red Kite that was killed during a specific month was found by a searcher during that month given it was in the Study population searched area. This method assumes that carcasses not found dur- 2 ing one search can be found during another search with the same Red Kites breed throughout the 29,483 km of the large Ger- probability, given they persist. man federal state of Brandenburg with an average density of 2 Finally, p100 was multiplied by the proportion of carcasses 5.8 pairs/100 km (Ryslavy et al. 2011). The best available estimate expected to lie in the searched area, a. The proportion a was of spring population size is 1650–1900 breeding pairs (mean 1775; s obtained from the search radius r and information about the pro- Ryslavy et al. 2011), thus representing 8% of the global population portion of area searched within the search radius. First, we obtained (Bird Life International 2012). Most birds migrate to south-west s the proportion of carcasses within r based on the results from Hull Europe in winter (Bird Life International 2012) but small numbers and Muir (2010), who applied ballistics theory to model the dis- are found in Brandenburg in winter. During 1988–2010 numbers tribution of carcasses around wind turbines. For large birds, they showed an annual decline of −0.97 ± 1.27%. We lack information show a uniform distribution of carcasses from the tower up to a about the non-breeding part of the population which might be con- maximum distance of 85–95 m depending on turbine size. We fit- siderable in a species recruiting at an age of 2–7 years (Newton et al.