Bushwalk Australia

OK brains trust
How do pelicans and seagulls actually know that Kati Thanda is now filling up with flood waters? Do brine shrimp release pheromones into the air when the eggs hatch or something?

I don't think anyone knows for certain.
The only explanation I'm aware of is that they can hear or sense the distant thunder and vibration. Which isn't a very comprehensive answer.

I do remember sitting on the rocks atop Mt.Wills (not far from Falls Creek) early one morning during the '03 Alpine fires.
High overhead we watched a pelican heading north. Someone commented he was about 150km's from the coast and flying directly towards a very big fire.