As renewable energy technologies expand worldwide, conservationists are concerned about the potential negative impacts of these technologies on animals, especially birds. U.S. News and World Report examined the issue in an August 22 article, and found that among the five most common energy sources, solar caused the least amount of bird deaths per year, while coal caused the largest amount. Though the article emphasizes that bird fatalities from renewable energy are less than bird fatalities from other forms of energy, it also shows that the data available on the matter is really not that good.

Reporter Alan Neuhauser gathered data about bird deaths where it was available, from government agencies, academic institutions, nonprofit organizations, and governmental laboratories, including the Bureau of Land Management, solar company BrightSource, and the journal Biological Conservation. According to the data, while solar is estimated to cause 1,000 to 28,000 bird deaths annually, and wind 140,000 to 328,000, coal kills far more – about 7.9 million birds a year!

However, some of the numbers were from outdated studies, some were very loose estimates, and the studies used very different methodologies, making comparisons difficult. The numbers for bird deaths from solar power generation appear to be based on one solar farm, Ivanpah in California. A sample size of one is not good practice for industry estimates. The data included for wind energy was from 2009, when wind capacity was at 35,000 megawatts (MW). Wind capacity has almost doubled since then, to 61,000 MW this year, according to the American Wind Energy Association (AWEA). The 5-year-old data no longer accurately reflects total bird deaths from wind energy generation.

Most importantly, the different reports referenced by the article used different methodologies to estimate bird deaths, which means the data are not one-to-one comparable. For instance, the data on bird deaths caused by coal, which came from a peer-reviewed report published in 2013 by the journal Renewable Energy, counted the effect of coal on birds throughout its use cycle, from extraction to power generation to climate change impacts. While not expressly stated, it is likely the bird death statistics for the other power sources were confined to deaths during power generation alone, not counting climate change and supply chain impacts.

The data are not comparable within a specific energy sector either. The two estimates provided by U.S. News and World Report for bird deaths resulting from solar power generation vary significantly, by a factor of 28. The KCET public television network reported that the estimate of 28,000 bird fatalities from solar power, the upper limit of the range provided by U.S. News and World Report, is from Shawn Smallwood, of the Center for Biological Diversity. He called his figure the result of “back-of-the-napkin-level” calculations and said it was based upon assumptions he could not “verify as correct.” BrightSource, which provided the lower, 1,000- death estimate, operates Ivanpah, a solar thermal power plant in California. Its estimate is based on the number of bird carcasses recovered from the plant’s heliostats, but does not take into account carcasses that are scavenged by predators.

In addition, both estimates seem to confine themselves to concentrated solar power (CSP), a thermal form of energy which – as its name suggests – concentrates sunlight in intense beams of heat called “solar flux.” These beams of heat, which are known to sear bird feathers, are quite a different threat to birds than photovoltaic (PV) solar panels, which are cool and create no in-air obstacles to bird flight. The threat to birds from PV solar panels comes from their resemblance to water, which can lead birds to dive into them, a phenomenon called the “lake effect.”

Clearly, the threat to birds and other wildlife from renewable energies should be measured in a thoughtful, comprehensive way by peer-reviewed researchers. However, it is important to keep things in context. When the detrimental effects of fossil fuels are fully taken into account, particularly their emissions of carbon and harmful pollutants, they have a substantial negative impact on wildlife. And, when it comes to birds at least, buildings and cats are the main cause for concern: cats kill 1.4 to 3.7 billion birds annually, and buildings kill another 980 million.


Authors: Yi Xu and Laura Small