The crystal-clear images of digital TV may come with a hidden cost, scientists say: the lives of thousands of migratory birds that could slam into new communications megatowers constructed to transmit these TV signals.
To comply with federal regulations that require digital TV broadcasts nationwide by 2003, television stations across the country will be building an estimated 1000 giant communications towers. Ornithologists warn that the megatowers, which can be up to 400 meters high, will add to the already alarming tolls on bird populations. The annual casualty rate for birds smacking into towers in the United States is between 4 million and 40 million, according to Fish and Wildlife Service (FWS) biologist Al Manville. The number of towers over 60 meters--now about 45,000--is expected to double within a decade. Most of the carnage occurs during spring and fall migrations, especially at night under foggy or cloudy conditions, when birds head for the brightest object they can see.
Last fall, the FWS issued voluntary guidelines for the construction of bird-friendly towers, including height limits, lack of supporting guy wires, and white, infrequently flashing lights that are least attractive to birds. The agency also says it will invoke the full force of the 1918 Migratory Bird Treaty Act, which prohibits tampering with migratory birds. (In a 1999 case under the Act, a Utah electrical company was fined $100,000 and placed on probation for operating power lines that killed eagles and hawks.)
Experts stress that understanding of the lighting conditions that attract birds is key to reducing mortalities. Bill Evans, an ornithological activist in Ithaca, New York, says, "If we could find a safer flash rate to put on these towers, we could save 3 million to 4 million birds a year."