United Airlines is defending the poisoning of birds at Houston's biggest airport, saying it was for health and safety reasons.

But the airline said Wednesday that it didn't tell its contractor how to control the bird population, and will ask that other methods be considered next time.

The contractor laid out corn kernels laced with a bird-killing nerve agent at Bush Intercontinental Airport. People who work around the airport reported seeing grackles and pigeons fall to the ground. Bait manufacturer Avitrol Corp. says a lethal dosage usually causes death within an hour.

Airports commonly take steps to shoo away birds, which can be sucked into jet engines. In 2009, a US Airways pilot leaving New York's LaGuardia Airport safely ditched his plane into the Hudson River after hitting a flock.