Vulnerability of birds to renewable energy production
Renewable energy production can kill individual birds, but little is known about how it affects avian populations. We assessed the vulnerability of populations for 23 priority bird species killed at wind and solar facilities in California, USA.
Bayesian hierarchical models suggested that 48 percent of these species were vulnerable to population-level effects from added fatalities caused by renewables and other sources.
Effects of renewables extended far beyond the location of energy production to impact bird populations in distant regions across continental migration networks. Populations of species associated with grasslands where turbines were located were most vulnerable to wind.
Populations of nocturnal migrant species were most vulnerable to solar, despite not typically being associated with deserts where the solar facilities we evaluated were located.
Our findings indicate that addressing declines of North American bird populations requires consideration of the effects of renewables and other anthropogenic threats on both nearby and distant populations of vulnerable species.
Expanding global demand for energy have fostered rapid and recent worldwide development of renewable energy. For example, although commercial wind energy generation has occurred for nearly 40 years in the United States, capacity has increased nearly 300 percent since 2009. The current installed capacity is now greater than 107 gigawatts (GW) from approximately 59,000 turbines [1–3], with a projected capacity greater than 160 GW by 2030 [4].
Likewise, the capacity of utility-scale solar energy, including photovoltaic (PV) and concentrating solar power (CSP) technologies, has increased 9400 percent in the United States, from 0.4 GW in 2009 to greater than 38 GW in 2019, and is anticipated to exceed 75 GW within 5 years [5]. Worldwide, wind energy capacity (540 GW in 2017) and PV technologies (438 GW in 2017) are forecast to increase by greater than 60 GW yr−1 and greater than 80 GW yr−1, respectively, through 2025 [6,7].
This growth raises concerns about the potential impacts of renewable energy on the environment when shifting energy production from fossil fuels on wildlife species [8–11].
For example, substantial numbers of birds and bats are found dead at some wind and solar energy projects (e.g. wind turbines of many types and sizes, PV panels, CSP parabolic troughs and CSP power towers).
Fatalities of birds predominantly are thought to be caused by collisions with turbine blades, PV panels and heliostat solar reflectors, but birds also are killed by concentrated beams of sunlight at CSP power towers, unintentional grounding at solar facilities and drowning in wastewater evaporation ponds at CSP facilities [12–15].
Despite concerns about the sometimes large numbers of wildlife fatalities caused by renewable energy, population-level effects of fatalities are essentially unknown for nearly all species [16–20], with a few exceptions [21–23]. Within the United States, the best estimate is that 140 000–328 000 bird fatalities occur annually at modern monopole turbines, but this number is derived from data collated approximately 10 years ago and at 57 percent of current installed capacity [13].
Similarly, solar energy generation at 37 percent of current capacity was estimated to cause 37 800–138 600 bird deaths per year in the USA, with most of these fatalities in California [12,15,24].
However, these large-scale estimates do not account for the effects of renewable energy on populations of individual species, information that is crucial to taxon-based conservation efforts [19,25] and to understanding the vulnerability of community and ecosystem processes affected by birds [26].
Another weakness of these estimates is that they do not distinguish between impacts on locally breeding populations versus impacts that manifest on distant (hereafter ‘non-local’) populations of non-breeding birds that encounter renewable energy facilities on migration or when dispersing.
Given the loss of approximately 3 billion birds in North America since 1970 [27] and the ecological, economic and socio-cultural relevance of avian species [28], a major scientific priority is to understand and mitigate the many threats to bird populations. With the anticipated build-out of renewable energy facilities to meet state and federal emission reduction goals [29], a critical component of this priority is to understand species’ vulnerability to cumulative incidental deaths from renewable energy development.
We applied a comprehensive analytical framework combining geolocation via stable isotope analyses of bird tissue, current population trend data, literature-based survival and fecundity rates, and Bayesian hierarchical population models to evaluate the vulnerability to additional fatalities of a taxonomically diverse suite of 23 priority bird species killed at renewable energy facilities.
These species were selected based on stakeholder input using factors such as ecological value, conservation status, and frequency and risk of mortality at wind and solar energy generation facilities in California, United States. We focused on California because it is a global biodiversity hotspot [30] and one of the world’s initial locations for wind and solar energy development and innovation (figures 1 and 2 and electronic supplementary material, tables S1 and S2; see Methods for detailed description of species and renewable energy site selection).
Our unique approach estimates the number of individuals present in both local and non-local regions (hereafter, local and non-local ‘catchment areas’) as a context against which we evaluate absolute vulnerability and relative risk to additional fatalities for each species, as well as taxonomic and ecological patterns of vulnerability.
This approach identifies the extent to which bird species are more or less likely to experience declines of a specified magnitude (i.e. their vulnerability), given the cumulative and range-wide mortality effects of many renewable projects together with other human-caused mortality sources.
We used expert opinion and ecological and conservation-related traits to identify a taxonomically diverse suite of 32 priority bird species for study (electronic supplementary material, table S1; also see [31]). We then estimated vulnerability for each using a five-step framework:
(1) determining the geographical origin of fatalities at renewable energy facilities,
(2) defining the geographical ‘catchment area’ encompassing the fatalities and estimating the size of subpopulations within those catchment areas,
(3) building species-specific demographic models to estimate rates of survival, fecundity and population growth,
(4) assessing species- and subpopulation-specific vulnerability with sensitivity analyses to estimate the demographic effects of additional fatalities, and
(5) evaluating taxonomic and ecological correlates of vulnerability (figure 2). Steps 1–4 of this process are defined in Katzner et al. [18], implemented here with context-specific alterations and improvements (see electronic supplementary material for full details on the methods).
We obtained feathers from avian fatalities at renewable energy facilities in California, including from approximately 5–30 wind facilities at the Altamont Pass Wind Resource Area (APWRA) in Alameda and Contra Costa Counties [32] and six solar facilities in Riverside and San Bernardino Counties (figure 1).
The wind and solar facilities in these two areas represent a wide variety of technology and production types (e.g. wind turbines of multiple models, manufacturers and power generation capacities, as described in greater detail in the electronic supplementary material). We measured stable hydrogen isotope (δ2H) values in feather samples, together with information on moult location and scaled δ2H values of precipitation at the site of feather growth [33–35], to assign a local or non-local origin for each bird (i.e. its ‘subpopulation of origin’).
This assignment was based on whether the collection site (renewable facility) was located within the area of the species’ range that exceeded a 5 : 1 odds ratio (OR) threshold value [17].
We used information from species range maps, migration flyways in the western US, Bird Conservation Regions (hereafter ‘BCRs’) [36] and local and non-local subpopulation of origin assignments to delineate species- and subpopulation-specific ‘catchment areas’ [17,37] (electronic supplementary material, methods and figure S1).
Each local catchment area included the aggregate mean summary surface greater than or equal to 5 : 1 OR within the local BCR that contained the renewable energy facility of interest (i.e. wind facilities were in the Coastal California BCR (BCR 32) and solar facilities in the Sonoran and Mojave Desert BCR (BCR 33)).
Non-local catchment areas included the aggregate mean summary surface greater than or equal to 5 : 1 OR for all non-local complete or partial BCRs within the Central and Pacific flyways [38]. We excluded all full or partial BCRs within Mexico, as that country lacked species-specific population estimates.
Our results highlight, for the first time, distinct patterns of population- and subpopulation-level vulnerability for a wide variety of bird species found dead at renewable energy facilities. Of the 23 priority bird species killed at renewable facilities, 11 (48%) were either highly or moderately vulnerable, experiencing a greater than or equal to 20% decline in the population growth rates with the addition of up to either 1000 or 5000 fatalities, respectively (see Methods for detailed derivation of vulnerability).
For five of these 11 species, killed birds originated both locally and non-locally, yet vulnerability occurred only to the local subpopulation (table 1, electronic supplementary material, tables S5–S7; figure 3, electronic supplementary material, figure S4). Casualties of one additional species (white-tailed kite, Elanus leucurus) originated from only a local population, which was also vulnerable. For the other five species, dead birds originated from both local and non-local subpopulations and vulnerability also occurred to both.
These five species included western yellow-billed cuckoo (Coccyzus americanus occidentalis) and western grebe (Aechmophorus occidentalis) killed at solar facilities and tricolored blackbird (Agelaius tricolor), barn owl (Tyto alba) and golden eagle (Aquila chrysaetos) killed at wind facilities.
Beyond vulnerability, relative risk (i.e. based on the comparison between local and non-local fatality rates within a species, as defined in Methods) was disproportionately high for local subpopulations of horned lark, Wilson’s warbler (Cardellina pusilla) and burrowing owl (Athene cunicularia) affected by wind facilities; local subpopulations of western meadowlark (Sturnella neglecta), Wilson’s warbler and greater roadrunner (Geococcyx californianus) affected by solar facilities (table 1); and non-local subpopulations of western meadowlark and American kestrel (Falco sparverius) affected by wind facilities.
This study shows that many of the bird species killed at renewable energy facilities are vulnerable to population or subpopulation-level effects from potential increases in fatalities from these and other anthropogenic mortality sources. About half (48 percent) of the species we considered were vulnerable, and they spanned a diverse suite of taxonomic groups of conservation concern that are resident to or that pass through California.
The inference from these analyses applies to the set of focal species and taxonomic groups analysed here, which represent only a small fraction of all bird species killed by renewable energy facilities. Nevertheless, our models highlight the relevance of understanding species-specific, population-level vulnerability for these and other species. Although birds face many human-caused threats, focusing on species of concern that are found dead at renewable facilities greatly improves understanding of the impacts of these and other anthropogenic developments.
Critically, not only local but also non-local, and often very distant, subpopulations often were vulnerable to additional fatalities at California renewable energy facilities. This matters because nearly all environmental monitoring conducted at renewable energy facilities evaluates local subpopulations (e.g. [12–15]) to infer population-level consequences of fatalities.
Our results illustrate that such locally focused surveys may poorly predict the cumulative impacts of fatalities. This study, therefore, emphasizes the importance of assessing the origins of wildlife affected when interpreting consequences to wildlife populations of these, or any, types of anthropogenic activities.
Our vulnerability scores were based on fixed numbers of annual fatalities (1000 and 5000). While this magnitude of mortality is unlikely at any single renewable energy project, it is reasonable when considering cumulative effects of many renewable projects at once [20,55,56], or when considering renewable energy effects combined with other human-caused sources of bird mortality.
In fact, this study shows that because renewable energy may affect both local and non-local subpopulations (including distant subpopulations of migratory species [31]), cumulative effects of renewable energy probably are more extensive than previously understood, especially for migratory species. Such non-local demographic effects only rarely have been documented for renewables or for other anthropogenic mortality sources (i.e. [61,62]).
Although our models were relatively sophisticated compared with analyses used in many past evaluations of renewable effects on wildlife, data limitations prevented incorporation of some demographic processes (e.g. immigration, emigration, Allee effects) that can affect population responses to anthropogenic stressors.
Further, we assumed all anthropogenic-related fatalities are additive (i.e. not compensated for at the population level by density-dependent or other processes) [63], that fatalities are constant through time and across avian age classes, and that all simulated fatalities were adults (electronic supplementary material, table S3). Future research could evaluate these processes, as well as alternative assumptions, to improve understanding of renewable effects on bird populations.
For example, models addressing full annual cycles, accounting for density dependence, or taking a maximum sustained yield or potential biological removal approach could include detailed information on anthropogenic impacts in each part of the life cycle and may help identify cumulative effects of anthropogenic stressors.
However, unlike the approach we used, such analyses currently are limited to species with sufficient information to construct these data-intensive models [22,46,64,65].
Additionally, while our model and its associated assumptions may not reflect true population dynamics, our approach allows for an estimate of the upper limit of potential vulnerability because the absence of density dependence removes any demographic compensation for fatalities [22].
Some of these species-specific data issues could be addressed by increasing systematic data collection at renewable facilities. This is especially true given that rigorous fatality estimates are lacking for most species [66].
However, there is growing interest in many management and permitting efforts to reduce the number of surveys conducted at facilities. As such, future approaches similar to ours may become increasingly reliant on limited datasets to assess species fatality risk and vulnerability.
Adapting future models to work with limited datasets while still incorporating metrics such as density dependence, covariance in vital rates, temporal variation in simulated fatalities across multiple age classes, or other factors known to occur in populations affected by anthropogenic fatalities may be beneficial to ongoing efforts to assess species-specific vulnerability.
This is taken from a long document, and we reproduced selected sections. To see the entire document, click here: royalsocietypublishing.org
Header image: Windmills Kill
Please Donate Below To Support Our Ongoing Work To Defend The Scientific Method
PRINCIPIA SCIENTIFIC INTERNATIONAL, legally registered in the UK as a company 
incorporated for charitable purposes. Head Office: 27 Old Gloucester Street, London WC1N 3AX.Â
Trackback from your site.