Hundreds of birds were recently poisoned and killed at George Bush Intercontinental Airport as part of a "bird abatement project" — one which animal rights groups are calling cruel and inhumane.

On Saturday and Sunday morning, KHOU's I-Team captured video of birds mysteriously dropping from the sky. Pigeons and grackles were seen exhibiting seizure-like behavior, apparently only the beginning of the birds' slow deaths. Shara Kelly, a parking lot worker at the airport, shot video of a dying bird with her cell phone.

"It was right there for a long time just flipping and flipping and flipping," Kelly told KHOU. "And I was like, why are these birds dying like that, I don't know if it's something that somebody fed them."

In fact, the birds were fed something, a toxicant called Avitrol which is sold in the form of corn kernels. According to a statement from the Houston Airport System, the use of Avitrol is part of a cooperative effort with United Airlines to mitigate "uncontrolled wildlife" which "can have serious and even disastrous implications for virtually any type of aircraft flying in the skies today."

In spite of United's insistence that they have "complied with all necessary regulations," some are unhappy with the handling of the situation.

"These deaths look anything but humane," Dr. John Hadidian, a senior scientist for the Humane Society of the United States, told the station. "The birds that are dying after ingesting this compound are suffering and in great distress."

Dr. Hadidian and the Humane Society acknowledge the threat of bird engine strikes, harking back to the successful landing of a U.S. Airways plane on the Hudson River following a double-engine bird strike. However, the animal rights groups are seeking non-lethal abatement methods, which can range from noisemaking devices to planting pigeon birth-control pellets, to manage overpopulation.

“This program primarily includes the utilization of loud noises, in an effort to displace the animals, and the installation of traps, but can also employ the use of mitigation chemicals that have been approved for use by the Federal Aviation Administration, the United States Department of Agriculture and the U.S. Fish and Wildlife Service,” said Houston Airport System spokesperson David Hebert in a written statement.

Hebert added that the U.S. Fish and Wildlife Service reviewed last weekend's abatement project and "determined that all measures in question fall within the accepted regulatory guidelines."

Although Avitrol is a federally approved chemical and the product's website states that affected birds "are not in pain," the toxic agent remains quite controversial.

Dr. Hadidian said that several local and state governments, including San Francisco, Boulder and the State of New York, have banned the use of Avitrol entirely. "I trust my eyes and I look and say that is a horrible way for an animal to die," he said.

While the U.S. Fish and Wildlife Service said that no violations occurred over the weekend, it did assert that the Houston Airport System may not have reported all bird deaths as required last year. A spokesperson for the agency said it plans to send a letter to Houston airport officials requesting further information.

See the KHOU report here: