The Australasian bittern usually hunts at dawn and dusk (2), or sometimes at night, and predates fish, frogs, crayfish and aquatic insects (7). It has also been recorded feeding on lizards, birds, rats, mice, leaves and fruit (2) (3) (5). When hunting, the Australasian bittern may keep still for minutes at a time before lunging at its prey, or it may keep its head and neck parallel to the water’s surface and sway its head from side to side. The Australasian bittern may eat its prey whole or shake or beat it to subdue it. This species has also been observed using grass to bait fish (2) (3) (5).
The Australasian bittern is a solitary bird that is often heard but not seen due to its effective camouflage. When disturbed, the Australasian bittern stays completely still and will blend into the vegetation by compressing its plumage and pointing its bill upwards. Alternatively, it may lower itself down gently into the reeds and rushes (2).
The mating call of the Australasian bittern can be heard in spring and early summer (8). Males will emit very deep 'booms' in a series which can last about 10 to 15 seconds, and these calls can be heard up to a kilometre away (2).
The Australasian bittern breeds in single pairs, from October to February in Australia and from September to November in New Zealand (2). This bittern nests in vegetation stands in swamps, and usually builds its nest about 30 centimetres above the water level, with the nest itself consisting of a platform of reeds, rushes and grass. Generally four or five eggs are laid per clutch. The female Australasian bittern incubates the eggs for about 25 days and, once the eggs have hatched, the female alone feeds the juveniles until they are about 7 weeks old, when they fledge (2) (3).