It would involve feeding them a mixture of green beans and human birth-control medication, but more study was needed to determine the method's safety and effectiveness, said Sitthisat Jiemwongphat, director of the Bangkok Metropolitan Administration (BMA)'s health department.

The BMA was concerned about the number of pigeons in the city, especially in Sanam Luang, Wat Suthat Thepwararam, Wat Mahathat, and the Sao Ching Cha (Giant Swing) and Silom areas.

Laboratory tests by the Livestock Development Department show the bird-flu virus has spread to migratory birds such as sparrows, pigeons and mynas.

"Firstly, the BMA will launch a campaign simply asking the public not to feed birds and asking vendors not to sell bird feed," Sitthisat said.

He said the BMA was working on ways to limit the pigeon population and would consult with Kasetsart University to conduct research on birth-control methods, and other ways to contain bird numbers - without killing them, he said.