As promised, I spent some time reviewing the scientific literature on wind farms and their impacts on bird populations. While the details are complex (and I will get to some of them), the short answer to the question, “Does wind power kill birds?” is, “Yes.” The longer answer is, “Yes, and so do all other forms of power generation currently in use. Generating power kills birds.” The still longer, and better, answer is as follows:
First off, the topic of birds and wind power is far too broad for my poor capacity here on this blog. The issues involved in land based wind farms are different from ocean based ones, and wind turbines affect different species of birds differently. This is not to mention the additional suite of circumstances around wind turbines and their effects on bats. I can’t cover it all. So, since this is the SEANET blog, I elected to restrict myself mainly to an investigation of the impact of ocean-based wind power on seabirds. That’s in itself a broad topic, but here goes.
A wind farm off the shore of Denmark. (Photo by Koppelius).
Wind farms can kill or harm birds in more ways than one might expect. There is the obvious and violent spectacle of birds killed due to direct flight into the turbine blades or the support structure. But there are subtler impacts as well. While the wind farm is being constructed, birds will be displaced substantially from that location by all the activity. Once construction is complete, the human presence is much reduced, but the turbines themselves alter the seascape from ocean floor to the tip of the tallest blade. The footings and pylons holding up the turbine disrupt and reduce the area of ocean floor and water column available for foraging, and birds may well steer clear of an extended area around the farms. If that area was a rich hunting ground, then the birds will suffer for its loss. How much? Depends on the wind farm, depends on the bird, depends on the prey. Up above the water’s surface, in addition to birds that are killed outright by the turbine blades, there are the birds that instead fly around them and pass by safely. But how far around do they fly? If, for instance, on a migration, a flock of birds gives a wind farm a very wide berth, they will have to increase their energy use for the extra flight time. That demands extra foraging to make up the lost calories. For some species where survival is on the slimmest of margins energetically, might this tip the balance?
While there are currently no offshore wind farms in the United States, Europe, led by Germany and its much touted Energiewende, have been investing heavily in such farms, and this gives us an ever increasing body of scientific literature on the observed impacts at real-life sites. Here in the U.S. many scientists have been using mathematical models to game out what impacts wind farms of various sizes, heights, and locations might have. Taken together, we gain ever more insight into how to sensibly and responsibly navigate the way toward cleaner energy sources.
Pulling out just a few papers, it becomes clear how unclear the answers become when we try to group even all seabirds together and assess risk. Collisions with turbines are fairly rare in seabirds overall, and especially in comparison to some nocturnally migrating songbirds, for instance. Many water birds actively avoid the turbines, flying above or below the blades, or around the entire farm. A 2012 study using radar detection of migrating pink-footed geese found that 94.25% of all flocks identified flew safely around the farm. Other species, however, are less successful in avoidance; a 2013 study in Scotland identified gulls, gannets and skuas as being at higher risk for collisions, and white-tailed eagles appeared to show little to no avoidance behavior.
As to the issue of loss of foraging grounds, the impacts will vary from species to species. By way of example, however, I can offer up the Black Scoter, and a study out in January from researchers in Rhode Island. This paper points out that while many species of seabirds will avoid a newly built wind farm, they will often begin to return to forage in the area after three years or so. It seems that many birds are able to acclimate to the presence of the turbines. A similar phenomenon has been observed at land based farms, where mortality from collisions declines over time as the birds learn that the turbines are there and adjust their flight patterns accordingly. In a species group that tends to be very long-lived, like seabirds, we could certainly anticipate that the knowledge a bird gains about where the farms are and how to work around them, once acquired, would continue to serve that bird over its potential decades of life.
An aggregation of scoters. (Photo: Kevin T. Karlson).
But let’s assume that the birds leave the area of a new wind farm and never return. What does that mean for the species? Again, it depends on the species. Black scoters are only loosely tied to particular foraging waters. Even in the absence of any offshore development, individual birds may spend the winter off Rhode Island one year, but the next year be somewhere closer to Delaware, or Cape Cod. In a species with this kind of flexibility, the impact of losing the foraging territory may be minimal since the birds are quite accustomed to moving around and trying new spots. But in a species with greater site fidelity, a poorly placed wind farm could have profound effects. That, in turn, leads us to the question of how we define well versus poorly placed wind farms. Rhode Island, Massachusetts and North Carolina are all examples of governments who have chosen to take on the process of marine spatial planning. They have realized that random and haphazard development of the marine environment could mean catastrophe for wildlife. By taking a rational, evidence-based approach, these plans lay out the best and worst places to site a wind farm or other offshore development project. Black scoters forage for invertebrates like mussels relatively nearshore, over hard bottom or coarse sand, and in relatively shallow waters. A wind farm placed in an area that matches those characteristics would be highly likely to impact Black scoters. The same farm shifted out of Black scoter prime range? Rather unlikely to have a major impact. Take a look at this figure from a 2013 paper by Winiarski, et al:
Figure from the Winiarski, et al paper on marine spatial planning.
On the left side are maps of the Block Island area showing the relative importance of the habitat to scoters. The darker the area, the more critical the habitat to bird survival. Darker areas are classed therefore as “priority habitat.” On the right side are graphs showing various species or species groups and how they are projected to decline based on how much of their habitat has been made inaccessible to them. Eventually, if you left zero habitat at all, there would be no birds left because they have no place to be. But up to that point, removing habitat will affect different species differently. The longer the colored line remains level, the more resilient that species is to loss of habitat, possibly because that species is flexible in its habitat use and can shift somewhere else. Other species with a more even distribution decline steadily as soon as habitat begins to become unavailable.
Moving down the figure, and looking at b) and c), we can see areas on the map that have been whited out completely. This is a simulated wind farm, and the model treats it as a total loss in terms of habitat. If a wind farm were sited there, we can look at the line graph and see some subtle shifts. Most notable in b): the reddish line representing Common Loons drops off quickly before leveling off somewhat. This indicates that the habitat chunk removed just west of Block Island is a particularly important one for loons. The change is c) is even more striking. There, the removal of a different piece of habitat to the southwest of Block Island causes a precipitous drop in the distribution of scoters, indicating that that area is of significant importance to their population. By manipulating these models, the scientists can come up with sites that we can expect will do the least harm. When habitat farther offshore, with fewer of the characteristics sought by seabirds, is removed in a simulated development project, the impacts on the birds are reduced. Such areas, shown in light gray in d) and e), would be better places for a wind farm, for the birds at least. For Rhode Island, the planning map thus recommends that wind farms not be sited within five kilometers of shore, or in waters less than 20 meters deep.
The key point of marine spatial planning is the planning. The creators of these maps and documents and guidelines realize that we need cleaner energy, and ocean-based wind is a huge potential source. By choosing the right location, we can also mitigate the risks to wild birds. Just like a LEED-certified, net zero office building is far superior to a conventional building in terms of sustainability, it would be irresponsible folly to construct it in the middle of a wetland housing the last population of a critically endangered species. We need clean energy, and we need to find the right places to get it.
To the question of whether or not we should be building wind farms at all, knowing they kill individual birds and pose some level of threat to the population, we must look at the alternatives. The fact is, we need power. The question is, where are we going to get it in the future. A 2009 analysis by Benjamin Sovacool sought to quantify how many birds are killed per kilowatt-hour of energy produced by various types of power, from fossil fuels, to nuclear, to wind. Some critics of wind power have pointed out that the reason so few birds are killed by wind turbines each year in the United States is solely because we have so few wind turbines. Scale up the technology, they argue, and the numbers of birds killed will skyrocket. Sovacool attempted to neutralize this factor by calculating not total mortality, but mortality per kWh, extrapolating out to an energy future where wind power is supplying far more of the grid.
Figure from Sovakool (2009). Blue shows annual avian mortality from each power source, and red shows mortality per gigawatt-hour of electricity generated.
Though his exact numbers have been challenged, and I agree with some of the critiques of his techniques and summation, his fundamental idea is sound. When we look at the entire fuel cycle of, say, coal versus wind power, we will come down on the side of wind being substantially more bird friendly. Sovacool points out that mining coal or drilling for oil destroys habitat for birds. Of course, building wind turbines does also. The most egregious methods of extraction, like mountaintop removal for coal, are the opposite of the kind of reasoned, strategic approach seen in a marine spatial plan. But turbines do disrupt habitat as well. Then comes the generation of power. Fossil fuel plants themselves kill large numbers of birds through collisions with their cooling towers and other structures, just as birds collide with cell phone towers and skyscrapers. Build something up into the air, and birds will hit it. An estimated 175 million birds are killed annually in collisions with transmission lines feeding the plants themselves. This issue of power lines remains for wind power too, of course; we have to move the power around and distribute it after all. So by some measures, it seems that the different power sources have similar liabilities in terms of avian mortality. Add in, however, the mercury and the acid-rain producing compounds that enter the atmosphere through the burning of fossil fuels, and the balance shifts to favor wind power. But even if we judged them equal up to that point, we’ve left out the greatest existential threat of them all: climate change. Whereas some species are more affected by wind turbines than others, it’s almost impossible to find a bird species that will be unaffected by climate change, and for some, it will spell extinction.
Sovacool also points to all the other anthropogenic causes of bird mortality: an estimated 100 million to domestic cats, 100-900 million dead by collisions with windows. “However,” he writes, “since house cats and office windows do not yet produce electricity, the comparisons are less relevant than those that assess avian deaths from other sources of electricity generation.” Less relevant to questions of our power supply, true, but the comparison is still useful. House cats are not inherently evil (though I know people who will argue that point), nor are office windows. House cats safely indoors are lovely pets to have. House cats hunting outside are a menace. Office windows are nice to gaze out of. Office windows illuminated at night when throngs of nocturnally migrating songbirds are passing through that exact geographic corridor are a killing field. Yet we see scant efforts at legislation to block new construction of office buildings, or even legislation to make windows in new construction less hazardous to birds. I don’t see legislation aimed at keeping house cats indoors either, and it’s not as if having a cat outside does us some essential service, as if it were a public utility. The fact is that knee jerk opposition to wind power on the basis that some birds will be killed by wind farms is not credible scientifically. Birds die by our actions in droves. We are always making the cost-benefit analysis of using cars, living in buildings, having cell phones and many other things that kill a lot of birds. We have the science on how to intelligently site these projects. We can put them where they will do the least harm to birds, knowing that the shift from fossil fuels to wind is, in itself, a benefit to birds. Not to an individual bird killed by a turbine, I’ll grant you that. But we are in the business of the population level threats. And those don’t get any bigger than our continued reluctance to shift to renewable energy.