Australasian bittern (Botaurus poiciloptilus)

The Australasian bittern (Botaurus poiciloptilus) is a large and stocky waterbird with a thick neck and camouflaged plumage ⁽²⁾. The upperparts of the Australasian bittern are dark brown to black, with mottled buff patterns to aid in camouflage. Its underside is pale yellow to buff with streaks of brown, while its chin and throat are pale ^{(2) (3) (4)}. This species has a thick, black stripe on the side of the neck and a pale stripe above the eye ^{(2) (3)}.

The Australasian bittern has a buff-coloured bill which is straight and pointed. Its legs and feet are pale green to olive, and its eyes are orange-brown to yellow ^{(2) (3) (5)}.All bitterns have long legs and toes which are useful for wading in swamps and wetlands ⁽⁶⁾.

Variation in the colouration of the Australasian bittern has been observed, with individuals showing darker or paler plumage, but this is not well understood ⁽²⁾. The male and female Australasian bittern are similar in appearance, but the female is smaller than the male ^{(2) (5)}. Juveniles are similar in appearance to the adult, but are paler and have a rufous-streaked underside and heavy buff flecking on the back ^{(3) (5)}.

The Australasian bittern has a characteristic booming call which can be heard during the mating season ^{(3) (4) (5) (7)}. A short, harsh ‘craak’ is given in alarm ⁽³⁾.

Also known as

Australian bittern, black-backed bittern, boomer, brown bittern, bull-bird, bullhead, bunyip bird.

Synonyms

Ardea poiciloptila.

Size

Length: 66 - 76 cm ^{(2) (3)}

Wingspan: 105 - 118 cm ⁽²⁾

Male weight: 875 - 2,085 g ⁽³⁾

Female weight: 571 - 1,135 g ⁽³⁾

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)}.

The Australasian bittern can be found in southern Australia, Tasmania, New Zealand and New Caledonia ^{(2) (3) (5) (7)}.

The Australasian bittern has specific habitat preferences, preferring shallow, freshwater wetlands with lots of tall reeds, rushes and other dense vegetation ^{(2) (7)}.

The Australasian bittern is classified as Endangered (EN) on the IUCN Red List ⁽¹⁾.

The Australasian bittern has a small and rapidly declining population, mainly due to the loss and destruction of its natural habitat ⁽⁷⁾. Its very specific habitat requirements means the Australasian bittern is very sensitive to loss of wetlands as areas have been drained for irrigation or to convert land to agriculture ^{(2) (7)}.

The salinisation (increasing saltiness) of its habitat is also a threat to the Australasian bittern, and high levels of grazing together with altered fire regimes are also further degrading the wetlands it relies on. In addition, the eggs of the Australasian bittern may be predated by introduced species such as foxes and cats, and the adult birds have been known to desert their nest if disturbed by humans ^{(2) (4) (7)}.

In Australia, there are already several sites dedicated to the management of the Australasian bittern population, such as Bool Lagoon and Lake Muir ⁽⁷⁾. In 2007, a Bittern Project was set up which aims to study the Australasian bittern and its habitats, raise awareness, and educate the local community in an attempt to limit habitat destruction ^{(7) (8)}. In Australia, the Australasian bittern is protected under the Environment Protection and Biodiversity Conservation Act ⁽²⁾.

Future conservation actions proposed for the Australasian bittern include surveys to determine accurate population estimates, as well as identifying and protecting this species’ habitats ^{(2) (7)}. It will also be important to rehabilitate former breeding habitat and involve community groups to help collect information and conserve this waterbird ^{(2) (4)}.

View information on this species at the UNEP World Conservation Monitoring Centre.

Find out more about the Australasian bittern and its conservation:

• Birdlife International - Australasian bittern:
  http://www.birdlife.org/datazone/speciesfactsheet.php?id=3767
• BirdLife Australia - Bittern project:
  http://www.birdlife.org.au/projects/bittern-project
• IUCN SSC Heron Specialist Group - Australasian bittern:
  http://www.heronconservation.org/styled-5/styled-7/

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

This species information was authored as part of the ARKive and Universities Scheme.

Incubate

To keep eggs warm so that development is possible.

1. IUCN Red List (November, 2012)
   http://www.iucnredlist.org/
2. Department of Sustainability, Environment, Water, Population and Communities (2012) Botaurus poiciloptilus. In: Species Profile and Threats Database. Department of Sustainability, Environment, Water, Population and Communities, Canberra. Available at:
   http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=1001
3. IUCN SSC Heron Specialist Group - Australasian bittern (November, 2012)
   http://www.heronconservation.org/styled-5/styled-7/
4. NSW National Parks and Wildlife Service (1999) Threatened Species Information: Australasian Bittern. NSW National Parks and Wildlife Service, Hurstville, New South Wales. Available at:
   http://www.environment.nsw.gov.au/resources/nature/tsprofileAustralasianBittern.pdf
5. McKilligan, N. (2005) Herons, Egrets and Bitterns: Their Biology and Conservation in Australia. CSIRO Publishing, Collingwood, Australia.
6. RSPB - Bitterns and herons (November, 2012)
   http://www.rspb.org.uk/wildlife/birdguide/families/bitterns.aspx
7. Birdlife International - Australasian bittern (November, 2012)
   http://www.birdlife.org/datazone/speciesfactsheet.php?id=3767
8. BirdLife Australia - Bittern project (November, 2012)
   http://www.birdlife.org.au/projects/bittern-project