Natural History Wanderings

The journal PLOS One published a study An Estimate of Avian Mortality at Communication Towers in the United States and Canada that reported on the large number of bird deaths associated with Communication Towers.  They estimated that 6.8 million birds are killed each year from collisions with the towers. To give perspective on the enormity of this problem the 1989 Exxon Valdez oil spill killed 250,000 birds. Ninety-five per cent of the birds that died are neo-tropical migrants such as thrushes and warblers.  The greatest number of deaths were associated with the tallest towers, steady burning red lights and guy wires.  It is unclear what causes birds to have difficulty dealing with the lighted towers.  Possibilities are:

• birds need a certain wavelength of light to sense the earth’s magnetic field
• bad weather and clouds black stars navigation resulting in birds seeing artifical light sources
• birds are drawn to the stimulus of bright light sources

It was estimated that the tallest two percent of the communication towers were responsible for 71 percent of the bird deaths.

Suggested actions that could reduce the number of bird deaths include:

• remove steady-burning red lights from tower leaving only flashing red, red strobe and white strobe lights
• avoid floodlights and other light sources at the bases of the towers
• avoid guy wires where practical
• limit the number of new towers by encouraging shared use of existing towers
• limit height of new towers

It was estimated that the tallest two percent of the communication towers were responsible for 71 percent of the bird deaths.  They recommend giving top priority to removing steady burning lights at towers over 150 meters tall.

To learn more go to sources for this positing PLOS One An Estimate of Avian Mortality at Communication Towers in the United States and Canada
and New York Times: Green blog A Lethal Beacon for Migrating Birds