As a marine bird, the diet of the Stewart Island shag consists primarily of fish but also marine invertebrates, sometimes even octopus, taken from water less than 30 m deep (2) (5). Pursuit-diving is the most common feeding method of the shag, whereby the bird dives from the surface and propels itself underwater using its powerful webbed feet (2). Shags, like penguins, are impressively agile at sea, but appear awkward on land. The behaviour of shags has given rise to many Māori sayings; someone obviously poised to leave is compared to a shag ready for flight, and the dejected air of a sitting shag gave rise to the phrase ‘as miserable as a shag on a rock’ (5).
The Stewart Island shag breeds all year round, and nests on exposed sloping rock in colonies of 10 to 500 nests. The nests are constructed from grass, twigs, peat and seaweed, cemented together with excreta and then lined with grass (2) (3). These can be massive nests, sometimes over one meter deep, into which two or three pale blue eggs are laid (2) (5).