Urban Jungle

August 10, 2010

More birds, more flights, more strikes

Aircraft collisions with birds reach a yearly peak in August

A summer's worth of breeding has swollen bird populations, with many of them gathering in flocks that increase hazards for pilots.

"There are at least twice as many birds in the population as in June," says Richard Dolbeer, a science adviser to the USDA Wildlife Services Program. "Recently fledged birds are inexperienced flyers and foragers . . . and are more likely to be struck by aircraft than the more experienced adults."

In the past 20 years, populations of large birds such as pelicans, eagles and geese have been steadily increasing, which has led to many more reported collisions with an ever-expanding fleet of airliners. Since 1990, 24 people have died in 10 such strikes in North America.

Airliners have become more vulnerable to the effects of colliding with birds. The more engines an airliner has, the less likely it is to be brought down by striking a flock. In the past two decades, two-engine aircraft have all but replaced three- and four-engine jets.

In January 2009, a US Airways flight departing New York's La Guardia Airport narrowly averted disaster when the Airbus 320's two engines failed after thrusting through a flock of Canada geese. Pilot C.B. "Sully" Sullenberger managed to land in the Hudson River; all aboard were rescued before the jet sank.

In the past 20 years, more than 1,200 Canada geese have been been hit by civil aircraft.

The abundance of nonmigratory giant Canada geese (a nine-pound jumbo subspecies) has mushroomed fourfold since 1990. Unlike their smaller migratory cousins, these geese generally stay put year-round, creating constant jeopardy for air traffic.

The USDA's Airport Wildlife Hazards Program assists with several methods for reducing goose hazards:

• Egg addling involves coating goose eggs with corn oil, which prevents respiration, halting embryo development.
• Harassment with pyrotechnic devices and other methods. The technique may drive the birds a few miles away, but they tend to return.
• Habitat alteration converts areas surrounding the airport into less- desirable goose territory. Access to water is blocked; grass that is unattractive to geese is planted and mowed to discourage both grazing and nesting.
• Depredation: Geese are shot or rounded up and gassed with carbon dioxide. If a poultry processing plant is available, the carcasses may be donated to a food bank; if not, they're either studied by scientists or buried.