Friday, May 9, 2014

Bird Deaths at Wind Farms (Part 1)

Growth of Farms Puts More Birds At Risk


A 2008 Department of Energy report calls for the U.S. to generate 20% of its electricity from wind by 2030. By then, experts expect wind turbines to kill at least one million birds each year, and probably significantly more, depending on how many turbines developers build over that time. Wind farms are also expected to impact almost 20,000 square miles of terrestrial habitat, and over 4,000 square miles of marine habitat by 2030, some critical to threatened species.

Deaths will come to birds who hold our identity and imagination, like Bald Eagles and other raptors. Turbines also kill birds listed as threatened or endangered unless developers carefully plan and implement wind farms. Onshore, these species include Golden Eagles, Whooping Cranes, sage-grouse, prairie-chickens, and many migratory songbirds. Offshore, species at risk include Brown Pelicans, Northern Gannets, sea ducks, loons, and terns, among other birds.

Scientists poorly understand the relationship of current fatalities to the demographics of bird and bat populations, but some experts do not see a problematic link between current wind farm fatalities and declines in bird populations (NAS 2007). My earlier post shows that other man-made structures cause far more bird deaths.  Domestic and feral cats pose the greatest risk to bird populations.

However, as wind energy facilities increase in number, fatalities and thus the potential for biologically-significant impacts to local populations increases (NAS 2007; Erickson et al. 2002; Manville 2009).

Mechanics of Wind Turbines

Early turbines were mounted on towers 60–80 feet in height with rotors extending 50–60 feet in diameter. The blades turned 60–80 revolutions per minute (rpm).
Today's land-based wind turbines are mounted on towers 200–260 feet in height with rotors 150–260 feet in diameter. The blade tips reach over 425 feet above ground level. Rotor swept areas now exceed 1 acre. Engineers expect the reach of the blade sweep to cover nearly 1.5 acres within the next several years. 

Under the current design, the speed of rotor revolution has significantly decreased to 11–28 rpm, but blade tip speeds have remained about the same. Under normal operating conditions, blade tip speeds range from 138–182 mph. 

For some disturbing video about bird deaths at wind farms, see here (Altamont Pass) and here (bird strike).

Wider and longer blades produce greater vortices and turbulence in their wake as they rotate, posing a potential problem for bats and small songbirds.

Engineers have reduced the number of turbines needed to produce a megawatt of electrical power by increasing the efficiency of each turbine. Accordingly, developers can generate power equivalent to older farms using fewer turbines that are more widely spaced. 

Still, Manufacturers are developing larger turbines.The one pictured here seems to be large enough for a helicopter landing pad and is destined for offshore use. 

The Research

In future posts, I'll discuss the current research on bird deaths at wind farms. Scientists/industry have conducted five major studies to date:
  • 2013 Smallwood Study: 573,000 bird deaths per year.
  • 2013 Canadian Bird Mortality Study: 233,000 bird deaths per year, and habitat displacement of 57,000 breeding pairs.
  • 2009 U.S. Fish & Wildlife Service Study: 440,000 per year.
  • 2013 Smithsonian-Sponsored Study: 140,000 to 328,000 per year (limited to monopole turbines).
  • Wind Industry Estimate: 58,000 per year.

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