In the past three years there has been a stunning and seemingly reckless increase in solar farms in California. Before 2013, solar farms covered four square miles of land. They now cover nearly 60 square miles and more are planned. (Here is a Google Maps file that shows the solar arrays in California; zoom in to see their actual footprints –or switch to satellite view.) They represent some of the largest solar arrays in the world. There are other smaller farms as well, and a few larger operations in Nevada, Arizona, and elsewhere. The majority, however, are in California.

*CSP = Concentrated Solar Power (essentially using mirrors to create a heat source)

Located mostly in the desert and Coast Ranges, they convert the sun’s rays to energy through several different processes: some use standard photovoltaic cells; others essentially boil groundwater with giant mirrors, creating steam to generate electricity. While all involve vast expanses of mirrors or solar panels, some include evaporation ponds and others have giant power towers collecting high intensity heat. Opposition has mounted regarding their massive footprint on the habitat, impacts on viewsheds, impacts to Native American artifacts and resources, impacts to the endangered desert tortoise, and, most especially, their massive impact on birds. This blog post details the last item.

The solar farms, probably each solar farm, are killing thousands of birds annually. From a distance, at the right angle, the arrays shimmer like water in the desert, attracting a variety of migrating loons, grebes, rails, pelicans, hummingbirds, swallows, thrushes, and warblers. For a list of 134 species found dead at various solar arrays, see Table B.1 of this report. The birds arriving at the solar fields crash into the mirrors, get burned alive by the reflected heat (called “solar flux”), or simply circle the arrays until they are exhausted. It is a strange thing to see, as I have, six exhausted Spotted Sandpipers crashing into a chain link fence in the desert, or to find a dead Red-breasted Merganser twenty-five miles from the nearest water.

Fortunately, there have been several comprehensive mortality studies at some of the solar arrays, with careful sub-sampling, and specific analyses of scavenging rates and search efficiency. Here is a summary of the results:

Ivanpah —a comprehensive report, HT Harvey (2015), estimated annual mortality at 2,496 to 5,705 birds , almost all songbirds. It categorized this impact as “low” because “Total detections (and fatality estimates) of any one species represent a small proportion of local, regional, or national populations.” (This is a common argument made by oil companies to dismiss the significance of oil spills.) And also because “the cause of death for 42.2% of the detections of species with 10 or more detections was unknown and thus cannot be determined with certainty to have been ‘facility-caused’.”

California Valley Solar Ranch —a comprehensive report estimated annual mortality at 4,048 birds (although this total is buried in the pages). Unlike the wide variety of species found at other sites, the majority of the birds impacted at this site are from just three species: Mourning Dove, Horned Lark, and House Finch.

—a comprehensive report estimated annual mortality at (although this total is buried in the pages). Unlike the wide variety of species found at other sites, the majority of the birds impacted at this site are from just three species: Mourning Dove, Horned Lark, and House Finch. Comprehensive studies are also underway at Topaz Solar Farm and Genesis , but they do not appear to be publicly available.

and , but they do not appear to be publicly available. A preliminary study, Kagan et al. (2014), did not systematically estimate annual mortality, but did find 141 carcasses in just three days at Ivanpah (where they observed one bird killed every two minutes at one point). They also collected 61 carcasses at Desert Sunlight and 31 at Genesis , suggesting significant impacts. These later two locations included a significant proportion of water birds, mostly grebes.

(where they observed one bird killed every two minutes at one point). They also collected 61 carcasses at and 31 at , suggesting significant impacts. These later two locations included a significant proportion of water birds, mostly grebes. California Solar One at Daggett—an early study was conducted in 1984 at this small prototype power tower (only 10 MW) and estimated mortality at only six birds/year (although apparently failing to adjust for carcass persistence). I cannot locate a copy of the study, but it is discussed in Turney and Fthenakis (2011) and Walston et al (2016).

It is understandable that Ivanpah would take such a toll. It serves a huge attractant for birds migrating across the desert and is visible from many miles away. The fact that they have even collected a dead Lapland Longspur suggests it is sucking in everything in its path and then some. What is no less disturbing is the take at California Valley Solar Ranch just north of Carrizo Plain National Monument. While probably less of a migration corridor, and using less reflective photovoltaic panels, the bird kill estimates are similar, although limited to local species. To the extent that they are simply wiping out resident birds, mortality may diminish with time simply because there aren’t any more birds left to kill. The two studies suggest bird kills between 500 and 1000 birds/square mile of solar array. If extrapolated across California’s 60 square miles of solar farms, the result is a staggering 30,000 birds per year. This is consistent with Walston et al (2016), just published in the journal Renewable Energy, who stated,

“We estimated annual USSE-related avian mortality to be between 16,200 and 59,400 birds in the southern California region, which was extrapolated to between 37,800 and 138,600 birds for all USSE [utility-scale solar energy] facilities across the United States that are either installed or under construction.”

[Walston et al. calculate bird mortality per MW of energy produced in order to compare the take at solar farms with birds killed at wind farms (which turns out to be about the same per MW) and fossil fuel use (which has a much higher mortality, although their analysis seemed crude at best). Studies at wind farms have revealed that most of the birds are killed by a minority of the wind mills (depending on blade type and location relative to ridges), suggesting there are ways to minimize mortality. Such information is not yet available for solar farms, although one small discovery at Ivanpah has been shown to help reduce bird kills in a limited context—but it is not the silver bullet that this public relations piece purports. The proper bird impact comparison for large solar arrays, however, should be to scattered rooftop solar in urban and suburban areas.]

The growth of the solar arrays (many of which are located on public lands) has been motivated by a number of policies that have both subsidized and fast-tracked their approval, and discouraged rooftop solar. California utilities are mandated to get a third of their energy from renewable sources by 2020, and rooftop solar does not count in that equation. In fact, in California there have been strong disincentives for installing more rooftop solar than you personally need, although new rules may help promote it.

Environmental Impact Statements for solar farms on large swaths of desert have been approved quickly and say little to nothing about bird kills. Some have offered “mitigation” in the form of protecting adjacent lands that are under no threat of development. The federal agency in charge of environmental review, the US Department of the Interior, is literally in bed with industry. At the same time, the investigation of bird kills is hampered at both the state and federal levels. As long as the power companies have the full blessing of Governor Jerry Brown and the California Energy Commission, other state agencies are limited in their ability to enforce environmental regulations. Federally, President Obama has lauded the Ivanpah array, while Republicans are seeking to gut the already-rarely-enforced Migratory Bird Treaty Act, the primary tool the feds have to enforce most of the bird kills (since the number of endangered species impacted is small).

Walston et al (2016) calculate that “full build-out of the nearly 48 GW of potential future USSE developments may account for as many as 480,000 bird deaths annually in the United States.” Here is what is needed:

Comprehensive mortality estimates at all sites

The comprehensive studies at a few sites, taking into account the difficulty in finding carcasses and the rapid removal of carcasses by ravens, are very welcome. They all need to be available to the public. Because impacts are likely to vary from site to site depending on the type of mirrors, panels, technology, and geographic setting, these studies should be replicated at all sites. It would be interesting to know, for example, the difference in impacts between Ivanpah (which resembles a lake in the desert) and Mount Signal (less reflective photovoltaic panels surrounded by green agricultural land and near a large lake).

Most of the reports attempt to minimize bird impacts with nonsensical statements at odds with basic biological facts. They note that an unspecified proportion of the dead birds may be naturally occurring (as if a solar array provides habitat for these species), that the majority of birds die from unknown causes (heart attacks?), and cast doubt on the “lake effect” of the reflective panels because the proportion of water birds is not always high (ignoring that swallows and migrating songbirds over the desert are attracted to water as well).

This is standard industry fare, but reports that minimize bird deaths or cast doubt on the “lake effect” are both ludicrous and not helpful. Because hazing is notoriously difficult and anything short of removing the mirrors is unlikely to stop attracting birds (one report suggested marking the mirrors to show birds it is not water—which seems highly unlikely since birds will fly into a window within twelve inches of a decal), it is likely the industry will simply continue to deny the severity of the problem. Serious solutions are needed, and this requires honest and transparent studies.

Stop building solar farms and support rooftop solar

Both the state and federal governments should stop the subsidies, loan guarantees, and public land give-aways immediately. They should give environmental enforcement back to the appropriate agencies. They should also do everything to promote rooftop solar so that it becomes integral to the grid.

Explore creative ways to minimize mortality, such as decoy habitat adjacent to solar arrays

One possible strategy to minimize mortality would be to encircle these facilities with suitable habitat that would intercept birds attracted to the panels from a great distance. For songbirds, stationing small clumps of trees (even fake trees) and water drippers, at intervals around the edges of an array, would provide cover and a stopping point for migrating birds. Ideally, they would prevent the birds from further flying around the array until they are killed. These way-stations would be small enough to not be visible until birds already attracted by the mirrors get close. Arriving songbirds would be attracted to the trees, outside of the solar arrays, much like a vagrant bird lost over the sea is attracted to the few trees at the lighthouse at Point Reyes or the two trees on Southeast Farallon Island, or a warbler over Lake Erie is attracted to Point Pelee, or other migrants over the desert are attracted to the trees at the Silver Saddle Ranch near Galileo Hill, the community of Desert Center, or the Furnace Creek Golf Course at Death Valley. They could rest, drink, recover, and move on from tree clump to tree clump until they are beyond the facility.

For water birds, a pond of real water, outside but near the array, would have to be provided as an alternative, perhaps with some cattails to signal it is real water. It would need to be long enough to allow for loons and grebes to take off and land. Such a pond was built at Searles Dry Lake near Trona. Hundreds of birds still die each year in the four-square miles of hypersaline discharge, but that mortality is reduced probably ten percent or more by a single one-acre pond that frankly could be improved; it looks very industrial.

Further evidence for the success of an alternative pond with real water comes from Solar One near Daggett in the 1980s, where an adjacent pond may have accounted for low mortality there, and at Ivanpah today. The Primm Valley Gold Course, a green oasis in the desert with several small ponds, is less than a mile from the Ivanpah array and may explain the relatively low proportion of water bird impacts there. In contrast, the total lack of alternative water around Desert Sunlight and Genesis is correlated with relatively high water bird mortality.

While this recommendation makes perfect sense to birders, it is at odds with current government thinking. Presently, the USFWS forbids any provision of water near solar arrays, not wanting to provide a water source for ravens, which prey on the desert tortoise (and extensively scavenge the dead birds). Any ponds within the array fields are netted to avoid creating more of an attractive nuisance. For songbirds, water drippers could be fenced to exclude ravens but allow smaller birds. There would be no way to exclude ravens from a pond for water birds.

I offer no guarantee these ideas would work, but they and other creative solutions should be researched immediately.

Compensate for the impacts through bird restoration projects

Obviously, large numbers of birds are being removed from their populations. These can be compensated for by restoring riparian habitat and other efforts that “create” more birds. Ivanpah has proposed donating funds to feral cat spay-and-neuter programs to help offset their bird impacts. It’s a nice gesture, but the idea: 1) is of highly questionable utility; and 2) does not really create birds.