Brown Skua
Catharacta lonnbergi

The Brown Skua (also known as the Southern Great or Antarctic Skua) is a large bird (120-160 cm wingspan) that can aggresively attack other birds to make them disgorge their own food, but is also quite a fearsome hunter, mainly eating ther birds. They occur around Antarctica and sub-antarctic islands in the summer and disperse north in the winter.
 

1: Tasman Sea, off Wollongong, NSW, 26/06/2011.
2: Tasman Sea, off Wollongong, NSW, 23/06/2012. 3-4: Tasman Sea, off Sydney, NSW, 14/08/2010.