## Is a windmill a mean bird killing machine?

How many birds are killed by windmills?

A windmill rotates at about ten revolutions per minute. This seems slow, but if you calculate the speed of the tip of the rotor, that's really fast. A quick calculation for the windturbine “Enercon E-126” (i.e. the windturbines at the windfarm of Estinnes-au-Mont, Belgium) gives us a speed of:

v= 2π*r / T = (2π* 63.5 m) / (60 s / 10) = 66,5 m/s = 239 km/h

with

v = the speed of the tip of the rotor
r = the radius of the rotor
T = the period of one rotation
π = tau / 2

If the tip of the rotor hits a bird, it doesn't stand a chance.

I estimate [1] that each year about 1 750 000 birds are killed by wind turbines in the United States. This number seems like a lot (that's because it is a lot), but it is much less than other causes of bird mortality (see below). Cats kill a whopping 276 000 000 birds a year in the US [4]. Of course, this does not mean that it's a good idea to install a wind farm next to a bird sanctuary.

The following representation shows the yearly death toll of birds in the U.S.

windmills:

1 750 000

traffic:
† † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † †
57 000 000

collisions with windows (birds are not always smart)
† † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † †
97 500 000

cats:
† † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † † †
276 000 000

Footnotes:

[1] Lomborg estimates that 70 000 birds are killed each year in the United States [2], based on data of the year 1998. In 2012, the installed wind power capacity in the United States increased by a factor of 28 [3]. This does not mean that there are 28 times more wind turbines installed; the height and power of each wind turbine has risen sharply compared to 1998. Let us do a pessimitic estimate and assume that about 25 times more fatalities occured compared to 1998, i.e. 1 750 000 birds die each year in the United States by windmills.

[2] Lomborg, Bjørn. The Skeptical Environmentalist: measuring the real state of the world. Cambridge Univ. Press, Cambridge (2001). ISBN 0-521-80447-7. Page 135.

[3] BP Statistical Review of World Energy, June 2013, London, UK.

[4] Lomborg estimates [2] that 9 million cats in the UK kill each year about 55 million birds (give or take a few), i.e. 0.9 birds per Brit. Since I find no reason why Americans would own more or less cats than British people, and since I see no reason why British cats would be more bloodthirsty than American cats, I pose that each year 276 million birds are slain by cats in the U.S.