I'm eastern Melb,foothills of the Dandenongs so as you can see my block is basically vertical.
I've also seen wattlebirds attack birds twice their size. I suspect they keep out some non natives as well as unfortunately some actual natives.
I saw one last year try to hassle the local kookaburra couple, who usually they seem to ignore, the wattlebird had snapped at the tail feathers of the kookaburra and was hanging on for probably full minute, the kookaburra looked like they'd barely noticed.
We don't get deer to our place (yet) but they're probably only a km or two away in the forest, plenty of foxes and rabbits though.