Well. Not the kind of birds with two flipping wings. In fact it has a set of propellors, weight almost 5 tons, and made loud "woo woo woo" sound when they fly passed our office building at around 2:30pm in the afternoon.
They were in fact UH-60 Black Hawk helicopters, and I was fortunately enough to have a camera with me to take these footages:
Looks like the Australian Defense Force is doing training here to respond to security-related incidents. Cool.