As we decrease our use of fossil fuels for energy production and increase our reliance on alternative energy production, organizations such as the Audubon Society have publicized worries that wind farms will increase bird mortality (Bryce, 2016). Such concerns should be handled seriously, considering US wind turbines currently kill between 140,000 and 328,000 birds annually (Loss et al., 2013) and killing of many of these bird species is considered illegal under the Migratory Bird Treaty Act, Endangered Species Act, and the Bald and Golden Eagle Protection Act (Erickson et al., 2005). Given wind turbine placement is best in areas with increased wind and that migrating birds selectively use winds to decrease flight costs in migration (Alerstam, 1979), it should not be shocking that bird mortality has been shown to increase during migration (Jain et al. 2009a), further posing a problem to wind power development under the Migratory Bird Treaty Act. Donald Trump has even brought up this issue in arguing against increasing wind energy and phasing out coal stating, “And [wind energy] kills all the birds. I don’t know if you know that… Thousands of birds are lying on the ground. And the eagle. You know, they put you in jail if you kill an eagle. And yet these windmills [kill] them by the hundreds” (Galloway, 2016).
Annual bird fatality due to wind power in comparison to other anthropogenic causes of death and other energy sources, however, can place the threat of wind turbines in perspective. Currently, wind turbines account for less than 1% of annual anthropogenic bird mortality whereas building collision, power lines, and cat predation in sum account for 82.5% of annual anthropogenic bird mortality (Erickson et al., 2005). Even amongst energy sources, Sovacool (2013) estimated that wind energy has only 0.269 avian fatalities per GWh, compared to 5.18 avian fatalities per GWh for fossil fuels and 0.419 avian fatalities per GWh for nuclear power.
If we were to achieve carbon neutrality by 2050 following Socolow’s stabilization wedges, wind energy and nuclear energy would need to increase relative to fossil fuel production (Pacala and Socolow, 2004). Even more so, following the Department of Energy’s “Wind Vision” plan, wind energy in the form of both on-shore and offshore wind farms will increase to 35% of our energy portfolio (U.S. Department of Energy, 2015). Wind farms can, though, intersect with the typical pathways through which migrating birds fly during migration, known as “migration flyways.” Thus, looking at whether certain migration flyways are disproportionately affected by turbines is important for placement of on-shore turbines, and projecting how bird mortality per year changes due to a changing energy production portfolio is important to understand implications on bird conservation. Such results could aid in advocacy for conservation and renewable energy, as well as determine if following through with different carbon emissions mitigation strategies decreases violations of the Migratory Bird Treaty Act.
Here, I first analyze if on-shore wind turbines disproportionately affect certain migration pathways, which could be the case if certain migratory pathways are more heavily trafficked. Then, using current data on the U.S. energy production portfolio, projected energy production, and avian mortality rates, I estimate current annual avian mortality in 2050 and project future avian mortality should we 1) continue with business as usual, 2) implement Socolow’s stabilization wedges, or 3) adapt the Department of Energy’s “Wind Vision” plan in conjunction with Socolow’s stabilization wedges.
Migration Pathways and Avian Mortality
Methods. In order to see if wind turbines placed in certain migration pathways have a disproportionate effect on bird mortality, I cross-referenced wind energy farm locations and capacity information (OpenEI, n.d.) and fatality/MW data from 21 locations (Erickson et al., 2004, 2008; Johnson et al., 2002, 2003; Howe et al., 2002; NWCC, 2010; Young et al., 2003, 2009; Nicholson 2001, 2002; Koford et al., 2005; Derby et al., 2007; Jain et al., 2008; Jain et al., 2009a, 2009b, 2009c). I then assigned each location to one of four migratory flyways as mapped by the U.S. Fish & Wildlife Service (2016; Fig. 1): the Pacific Flyway, Central Flyway, Mississippi Flyway, and Atlantic Flyway. I further determined the mean bird fatalities/MW/migratory pathway ± standard deviation (Fig. 2).
Figure 1: Map of U.S. migratory flyways. Adapted from U.S. Fish and Wildlife Services (2016).
Results. Although mean number of bird fatalities per MW differed between flyways, with the Mississippi Flyway having the highest mean number of bird fatalities per MW (5.265 ± 4.73), the variation in bird fatalities per MW suggests the flyways are not significantly different than other migratory pathways (Figure 2), and that migratory pathways had similar bird fatalities per MW of wind turbines within the range of uncertainty (Figure 2). These results therefore suggest that on-shore wind turbines do not disproportionately affect certain migratory pathways. Therefore, mitigation of avian mortality should focus on local site selection and modification of turbine function rather than broad-based location.
Figure 2: Mean ± SD bird fatalities per MW across the four US Migratory Flyways. Data sourced from: Erickson et al. (2004, 2008), Johnson et al. (2002, 2003), Howe et al. (2002), NWCC (2010), Young et al. (2003, 2009), Nicholson (2001, 2002), Koford et al. (2005), Derby et al. (2007), Jain et al. (2008, 2009a, 2009b, 2009c), and OpenEI (n.d.).
Effect of Carbon Emission Mitigation on Annual Bird Fatality
Methods. To assess current bird mortality and project future bird mortality by 2050 through 1) business as usual, 2) stabilization wedges, and 3) the implementation of the “Wind Vision” plan (Figure 3), I first accessed data on US energy production sources from the EIA “Electricity Data Browser” to obtain the total generated GWh and GWh per energy sources (U.S. Energy Information Administration, n.d.) for 2015. I then multiplied fossil fuel energy, nuclear energy, and wind energy production by Sovacool’s (2013) calculated bird fatalities/GWh for each of these energy sectors. To determine bird fatality/year in 2050, I applied an EIA forecast of 24% growth in electricity from 2013 to 2040 (U.S. Energy Information Administration, 2015).
Using the 1-yr average in energy growth (0.89%) obtained from averaging 24% growth from 2013 to 2040, I forecast energy production in 2050 to be 5,519,435.81 GWh. I then broke down energy production between sectors using the 2015 energy portfolio. Then, I applied Sovacool’s (2013) rates of bird fatality/GWh for each sector to determine total bird fatalities/GWh. Following suit, I generated new energy portfolios where the added energy production between 2015 and 2050 was broken down by Socolow’s stabilization wedges (Pacala and Socolow, 2004) where 1/7 of added energy is produced by wind, 1/7 is produced by nuclear energy, and 2/7 is produced by fossil fuel. I was not able to get estimates for bird fatality/ GWh due to solar or hydroelectric; however, both seem to have a negligible effect on bird fatality (Turney and Fthenakis, 2011).
Then, I determined the energy portfolio for a 35% growth in wind farms by 2050 following the “Wind Vision” plan (U.S. Energy Information Administration, 2015a). The added energy production between 2015 and 2050 was split in a similar method following Socolow’s stabilization wedges.
Results. As a result of applying carbon mitigation proposals, bird mortality would actually be lower per year when compared to continuing with business as usual (Figure 3). In contrast to public concerns about wind, increasing the wind energy in our energy portfolio would lead to a decrease in the number of bird fatalities due to energy generation per year such that annual bird fatalities would be lower in 2050 than they were in 2015 despite a 31% increase in projected energy generation during this same period (Figure 3).
Figure 3: Bird fatalities/yr based on 1) switching to Socolow stabilization wedges’ energy portfolio by 2050, 2) continuing with “business as usual” and not shifting our energy portfolio, and 3) applying the “Wind Vision” report and expanding wind energy to 35% of our energy budget while applying stabilization wedges for carbon mitigation. Figure is made by author. Data is sourced from and projected based on U.S. Energy Information Administration (2015a, 2015b, 2016), Pacala and Socolow (2004), and Sovacool (2013).
Synthesis and Implications
Even though there are concerns regarding increasing wind farms in the U.S., particularly due to legal ramifications under the Migratory Bird Treaty Act, Endangered Species Act, and the Bald and Golden Eagle Protection Act (Erickson et al., 2005), increasing the proportion of energy generated by wind actually would decrease the number of avian mortalities due to electrical energy generation/year, particularly when done in conjunction with other mitigation strategies (Figure 3).
One limitation to these data, however, is that fatality other than direct kills (such as exhaustion of birds leading to increased mortality during migration or kills by power line electrocution; Manville, 2005) is not considered in this analysis. Other energy sources though, pose some of these same risks to birds – particularly that of power line electrocution. At present, power lines alone account for 130 million annual bird mortalities, 13.7% of annual anthropogenic bird mortality (Erickson et al., 2005). Therefore, decreasing a reliance on fossil fuels by increasing wind production and nuclear production would decrease annual avian mortality by avoiding fatalities that are due to fossil fuel extraction, combustion, pollution, and climate change. Contemporaneously, we can invest more research and technology in decreasing bird mortality due to public utilities like power lines, for which steps have already been taken (Manville, 2005).
It is clear that, contrary to public and to Trump’s opinion, increasing wind energy would theoretically benefit bird population viabilities. As research into mitigating and avoiding avian mortality increases, technological advances could potentially further decrease annual mortality rates. Given that available data indicate that migratory pathways do not have significantly different avian mortality rates due to wind turbines (Figure 2), variation in mortality rates could be due to wind energy management and differences between specific wind turbines and size of wind farms. Currently, research is being conducted to further mitigate mortality rates at and around wind turbines. For example, determining diurnal and nocturnal migration densities and locations around proposed and developed sites could determine peak migration times. Avoiding building wind turbines in these sites would decrease future mortality, and turning off currently functioning turbines during these times can decrease both current and future mortality (Hüppop et al., 2006). More work should also be done though in deciphering what types of wind turbine structures and management allow birds to better recognize and avoid wind turbines.
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