FCC on Tower Kills

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FCC on Tower Kills

Postby jon » Fri Nov 16, 2007 9:37 pm

The FCC deadline for comments was last April, but I only read about this recently.

The death of migrating birds is a real issue, but the only well documented evidence is for office buildings. As I recall, certain reflective coatings on office windows cause birds to see open sky ahead, when it is really a mirror image of what is behind them. The University of Alberta is currently doing a study using some of its buildings by simply placing black flying bird-shaped stickers on their windows.

I've also seen songbirds that are migrating through this area, dead below the windows of downtown office buildings early in the morning.

But this is about radio, television and other communications towers, and their guy wires. I cannot see how birds could hit them.

http://www.towerkill.com/indexb.html - has the info below and huge amounts of additional info.

Towerkill Mechanisms

Two independent mechanisms of bird mortality occur at communications towers. The first is when birds flying in poor visibility do not see the structure in time to avoid it (i.e., blind collision). This is more of a threat for faster flying birds such as waterfowl or shorebirds; variables in bird vision and flight agility are factors - slower, more agile flying birds, such as songbirds, 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.

Communications towers that are lighted at night for aviation safety may help reduce bird collisions caused by poor visibility, but they bring about a second mechanism for mortality. When there is a low cloud ceiling or foggy conditions, lights on a tower refract off water particles in the air creating an illuminated area around the tower. Migrating birds have lost their stellar cues for nocturnal migration in these weather conditions. In addition, because they are flying beneath a relatively low cloud ceiling, they have lost any broad orienting perspective they might have had on the landscape. When passing the lighted area, it may be that the increased visibility around the tower becomes the strongest cue the birds have for navigation, and thus they tend to remain in the lighted space by the tower. Mortality occurs when they run into the structure and its guy wires, or even other migrating birds as more and more passing birds cram into the relatively small, lighted space. It is important to clarify that the lights apparently do not attract birds from afar, but rather tend to hold birds that pass within a certain illuminated vicinity.

In the 25-year study of bird mortality at the 1010-foot tower at Tall Timbers Research Station near Tallahassee, Florida, kills occurred nearly every night from mid-August through mid-November. Moderate numbers of migrants were killed under perfectly clear skies, but the toll increased markedly with overcast conditions. Theoretically the small kills on clear nights were not from birds drawn to the tower lights but from birds that happened to be flying near the tower and didn't see a guy wire - blind collision. The bulk of the kills on overcast nights likely involved the phototactic mechanism. The majority of mortality from communications towers is thought to result from this mechanism, and thus a number of studies have been conducted to further understand it.
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