Monday, October 10, 2005

Tower + Birds = Dead Birds?

You may have seen one of these headlines recently:

TOWER COLLISIONS CITED IN DEATHS OF BIRDS IN [insert city]
Hundreds of migrating songbirds were killed over one week apart after allegedly colliding with wires supporting an 1,100-foot television tower in _________, prompting wildlife experts to call for a probe of the phenomenon. Those investigating the incident wonder if illumination could prevent collisions.

MASS AVIAN DEATH TOLL AT [insert city]
As many as 400 songbirds were killed in one night after they flew into wires holding up a television tower. The deaths may spur the creation of a group to study the dangers communication towers pose to migrating birds, said specialists with the Department of Natural Resources. ______ want to form a task force of bird experts and communications industry representatives to study the issue. Possible solutions include using lights to illuminate wires and changing the blinking frequency of red warning lights,

There are two different mechanisms for bird mortality at towers.
1. Birds flying in poor visibility do not see the structure in time to avoid it. Some bird species are are not as likely to succumb to blind collision. This mechanism can occur during the day when the tower is obscured by fog, or at night, theoretically more often with unlighted towers
2. Birds use lights to navigate while migrating are actually drawn to the tower lights. They easily evade the tower itself but instead hit a guy wire. The majority of mortality from communications towers is thought to result from this problem.

blurb here too: http://web.syr.edu/~bpburtt/Birds/Aug08-04.htm
2nd here; http://www.newhousenews.com/archive/story1a051800.html

Ultimately the argument is brought up that turning off the lights would help.
But that would not help the AIRPLANES that are trying to avoid the towers as well.