Sulphur-crested cockatoos (Cacatua galerita) sharpening their beaks and/or geophagy (consuming sandstone to detoxify food). Even though these birds are very common in the city, this was the first time I observed their behavior in a natural setting. Around 33 seconds into the video you can hear their call. It is very noisy up close, and the sound is penetrating even from a great distance with strong winds.
Photographed and filmed in situ [1]