> The pigeon has not yet been caught, but the Department of Agriculture, Water and the Environment says it will have to be put down because of the _danger of infection to local birds_.

The problem (in this case) isn't the bird breeding, it's infections that it might carry. I can imagine it's possible there's a tonne of diseases it might carry that could be passed to the local native & agricultural bird populations that they have no exposure to.

Australia's relative isolation means that there's many diseases that local animal populations have no immunity to.