I think it's a beat-up and all the swans and seagulls should be able to freely walk around without masks

Clearly its fabricated and no pelicans or kookaburras will die.

Joking aside, I guess this is just one of these things where some birds will survive it and get immunity and many won't. I guess the concern is it spreading to chickens and the like.
I find it interesting that a bird can fly so far from another place with it and still make it to Aus. This suggests that the virus is not as vigorous as it might have otherwise been, which is often a pathway a virus takes.