Continental Airlines (CAL) banned shipments of adult poultry after a U.S. animal welfare organization raised concerns that the birds were used in the blood sport of cockfighting.

The Humane Society of the United States targeted the carrier after getting a tip that the airline was shipping roosters to Guam, where cockfighting is a popular and legal sport, a spokeswoman for the nonprofit group, said Tuesday.

"There's really no other purpose for roosters in Guam other than cockfighting," Ann Chynoweth, director of the Humane Society's animal fighting and cruelty campaign, said. "They have no agricultural purpose" on the U.S. territory.

In the centuries old sport where two or more specially bred birds fight as spectators watch or place bets, the roosters' legs are often fitted with sharp steel blades. The fights can result in one or both of the birds being injured or killed.

Julie King, a spokeswoman for Continental, said a complete embargo on shipments of adult poultry was the best solution because the airline found it unacceptable that birds were being used for illegal fighting.

Continental shipped about 6,000 adult birds from mainland U.S. breeders to Guam between 2001 and 2005, the Humane Society said.

King said the ban, which went into effect in October, has had a minimal impact on Continental's business.