Monday, November 26, 2012


Help for Chicago’s high fliers

A Northern Flicker, dead as a result of running into the window of a Chicago skyscraper. [Image credit: Annette Prince, Director of Chicago Collision Monitors]

A Generalist Investigation


Lots of birds die every year – most from natural causes. Lots of birds are killed by hunters, large numbers by cats. But I was unaware that, after habitat destruction, the biggest number of bird deaths are caused by plate glass and reflective windows – the full story of which follows.

As well as Window Kills, I have investigated bird deaths involved with power lines and the even more controversial subject of bird deaths caused by wind farms in subsequent posts.

Birds collide with lots of different kinds of man-made objects and below you will see some comparative figures from the US which gives annual death rates from these various causes and others. The figures differ in each case.

  The American Bird Conservancy published the chart below comparing US bird collision deaths from a number of causes. Data date with low and high estimates:

Wind turbines: 100,000 (2010) - 440,000 (2009)

Communication Towers: 2008                               4,000,000-50,000,000

Power lines: 2001  10,000,000-154,000,000

Roads/vehicles: 2005  10,700,000-380,000,000

Urban light: 2009  31,158,000

Glass: 2006 100,000,000 - 1,000,000,000

According to the Migratory Bird Mortality Fact Sheet produced by the US Fish & Wildlife Service.

‘Building window strikes may account for 96 to 976 million bird deaths each year.

Communication towers conservatively kill 4 to 5 million birds annually (probably closer to 40 to 50 million; a nationwide cumulative impacts study should help resolve this question).

Strikes at high tension transmission and distribution power lines very conservatively kill tens of thousands of birds annually. Taking into account the millions of miles of bulk transmission and distribution line in the US, and extrapolating from European studies, actual mortality could be as high as 174 million deaths annually. Electrocutions probably kill tens of thousands of birds but the problem is barely monitored.

Cars may kill 60 million birds or more each year, private and commercial aircraft far fewer

Wind turbines kill an estimated 33,000 birds annually.’

SEE ALSO: ‘Avian mortality from wind power, fossil fuel and nuclear electricity’ by Benjamin K. Sovacool (2009)

This contains the following chart, reproduced in the Wikipedia entry on the Environmental Impact of Wind Power which includes a broader range of causes of avian mortality.

Causes of avian mortality in the United States. Estimated mortality (in thousands)

Wind turbines 440

Aircraft 80

Nuclear power plants 330

Large Communications Towers (over 180', North America) 6,800

Communication towers (cellular, radio, microwave) 4,000 – 50,000

Fossil fuel power plants 14,000

Cars & trucks 50,000 – 100,000

Agriculture 67,000

Pesticide use 72,000

Building windows 97,000 – 976,000

Domestic cats 100,000

Hunting 100,000

Feral cats 110,000

Transmission Lines (conventional power plants) 175,000


Hawk eye

Hawkeye by Steve Jurvetson

Its worth asking why do birds collide with things. This is the subject of a fascinating paper which you can read here: ‘Scientists find bird-centric solutions to avian collisions’

'From a human perspective it appears very odd that birds so often collide with large objects as if they don't see them,' commented Professor Graham Martin from Birmingham University in the UK. He said that it is widely held that flight in birds is controlled primarily by vision, an idea captured by the phrase 'a bird is a wing guided by an eye,' but he pointed out that 'birds live in a different visual world to humans'.

       See also: ‘Why Birds Crash’ on The Naked Scientist

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