Cormorants are sleek, efficient predators which catch their prey after an underwater pursuit, whereby the fully webbed feet propel and steer the streamlined body forwards (2) (3). These birds have an unusually high volume of blood in their bodies, and the large amount of stored oxygen enables them to remain underwater for up to four minutes at a time (3). Owing to this unique adaptation, the imperial shag can dive as deep as 50 metres to catch its fish or crustacean prey under rocks or in kelp beds (4) (5). The inner feathers are waterproofed and insulate against the cold waters; however, the outer feathers become sodden, limiting hunting forays to only two bouts of 30 minutes before the bird must return to land to allow the waterlogged plumage to dry (3). Upon returning to land, the imperial shag assumes a characteristic posture and stands upright with the wings extended outwards, exposing itself to the sun to dry (3) (4).
At sea, the imperial shag may forage individually or in large flocks of thousands of birds, but when breeding, this bird always forms dense colonies, occasionally numbering as many as several hundred thousand birds (2) (4). Breeding pairs regularly change nesting sites between seasons, but competition for the best location is always fierce and breeding birds will engage in aggressive territorial behaviour. Typically this rarely goes beyond threatening postures, but on occasions when it does, fighting may ensue, with bill-grappling or birds seizing the opponent by the neck and wings (3) (4). The male bird gathers vegetation, mud and guano to build a simple cup-shaped nest in which a clutch of normally three eggs is laid (2) (4). Both the male and female take turns in incubating the eggs for around 28 days (3) (4). The chicks hatch naked and helpless, but grow quickly on an energy-rich fish diet and will fledge after around 75 to 80 days (4). After leaving the nest, the young birds may already be capable of flying, but if not, they gather together at sea in small crèches until they are strong enough to become fully independent (3).