|Australasian Bittern. Images courtesy of Richard Hall photography|
|Australasian Bittern |
The Australasian Bittern Botaurus poiciloptilus, sometimes referred to as the Brown Bittern is a seldom observed, well camouflaged and elusive species that inhabits well vegetated wetlands from southern Queensland, through New South Wales, Victoria, to south-eastern South Australia along with more isolated populations in Tasmania and south-west Western Australia. Populations also exist in New Zealand and New Caledonia.
The Australasian Bittern is one of three similar species that inhabit wetlands in south-western Victoria, the other two being the Nankeen Night Heron Nycticorax caledonicus and the Little Bittern Ixobrychus minutus, (particularly the juvenile plumage of these birds) but both being noticeably smaller than the Australasian Bittern.
The Australasian Bittern stands nearly a metre tall with a head and body length of up to about 75 cm. It is a thick set bird, mostly mottled brown, darker above with a creamy buff and brown streaked underside with a white throat and dark brown streaks along the side of the neck. In flight it has a general brown appearance with a large wingspan just over a metre.
|All records of the Australasian Bittern Source: Victorian Biodiversity Atlas, DEPI, March 2014|
Habitat and ecology
The Australasian Bittern has been recorded from both inland and coastal freshwater wetlands but many of these records are old and more information is required to ascertain the present day occurrence of this species.
The Australasian Bittern is considered to be partly nocturnal as it actively forages pre dawn and dusk. It can also be observed during daylight hours, particularly during the breeding season October to February (BirdLife International 2008) where it usually forages in shallow water up to 30 cm deep with dense wetland vegetation containing sedges, rushes, cumbungi or the common reed Phragmites.
Under suitable conditions when wetlands are more prolific populations can increase dramatically with the bitterns taking advantage of short-lived wetlands (Garnett and Crowley 2000). The population inturn shows declines after years with less desirable rainfall (BirdLife International 2008). Although generally sedentary the bittern will migrate in response to flooding or drought (Garnett & Crowley (2000).
There appears to be a lack of information on breeding and nesting ecology regarding the Australasian Bittern but it is generally accepted that a usual clutch size is 3-6. Nests are constructed in shallow water by trampling reed vegetation into a platform containing the nest.
Decline and Threats
A nomination for listing the Australasian Bittern as Endangered under the Environment Protection Biodiversity Act 1999 has been prepared. This document estimates there has been a decline in area of occupancy over 70% in last 30 years and that the total population in Australia might not be more than 1000 birds (EPBC Act nomination 2009). Also the IUCN Red List indicates that the Australasian Bittern population is in a declining trend (BirdLife International 2008).
In Victoria, the Victorian Flora and Flora Guarantee Act Scientific Advisory Committee submitted a final recommendation for listing of the Australasian Bittern in 1997. The committee considered that information on the Australasian Bittern is insufficient and the species population is in decline (SAC, 1997).
Factors which impact on the survival of the Australasian Bittern
Degradation of wetland habitat through changed water regimes
This could be due to drought, drainage of wetlands or changes within the catchment which either reduce or pollute water flow into wetlands, the net result being degraded habitat for the Australasian Bittern. A combination of drought and manipulation of natural water flows can have a dramatic impact on wetland health which in turn impacts on the viability of Australasian Bittern occupancy.
Degradation of the freshwater water table through over harvesting of water resources, poor catchment health including erosion, saline runoff and removal of native vegetation can contribute to rising salinity levels in wetlands. This can result in changes to the ecology of wetlands through reduced diversity of plants and animals, loss of freshwater wetland vegetation and a decline in the viability of wetlands for the Australasian Bittern.
Loss of wetland habitat caused by grazing
This has a direct impact on the Australasian Bittern through loss of foraging areas, loss of nesting habitat, reduced abundance of food and increased predation by foxes.
The introduced Red Fox is considered a major predator species, particularly eggs, chicks and immature birds before they can fly.
|Foxes and cats can prey on the Australasian Bittern Image: Richard Hall photography|
Suggested Management Actions
Management and restoration of wetland habitat and Australasian Bittern breeding sites in Victoria.
Restoration of wetland habitat that has been depleted due to human disturbance, by ensuring suitable water regimes are re-established and maintained.
Protection of wetlands and breeding sites on privately owned land in Victoria, through conservation covenants under the guidance of Trust for Nature or Wetland Tender and through Local Government Planning provisions.
Management of agriculture practices surrounding wetland habitat to reduce agricultural runoff and livestock grazing and trampling of vegetation.
Review of current local government policy of wetland drainage practices for urban development.
Strict planning regulations for new developments in close proximity to wetlands.
Protection against introduced predators, specifically foxes
Baiting and trapping of introduced predators in areas supporting breeding populations, on both public and privately owned land.
Further investigation of predator control methods to effectively control foxes and feral cats.
Further studies investigating the impact of foxes and other introduced predators on population fecundity and chick success.
Research, surveying and monitoring of populations in Victoria
Further research on the ecology of the Australasian Bittern.
Determine if there are any other factors that may limit or threaten survival of the Australasian Bittern.
Conduct intensive surveys on species distribution, population status and breeding data. Australasian Bittern Survey
Examine the merits of a captive breeding and release program for wetlands that have been re-instated and subject to protection.
Increase community awareness and participation in conserving wetlands and the Australasian Bittern
Inform local communities about presence and importance of threatened species such as the Australasian Bittern
Encourage community groups and organisations to become involved with the conservation of wetlands.
Encourage the public, community groups and bird associations to collect data on sightings of bitterns.
Provide assistance, management advice, information, resources and funding to private land holders who have wetland and bittern breeding sites on their land.
Promote and inform the public on placing covenants of privately owned land for conservation of wetland habitat.
DEPI (2013) Advisory List of Threatened Vertebrate Fauna in Victoria – 2013, Department of Enviornment, Land Water & Planning, East Melbourne, Victoria. DELWP Advisory Lists
EPBC Act nomination (2011) EPBC Act Listing advice to list in the Endangered Category 3 March 2011, pdf. Accessed 22 February 2017.
FFG Act (1988) Flora and Fauna Guarantee Act 1988, Victoria, Flora & Fauna Guarantee Act Listed Items 2014. Accessed 22 February 2017.
Garnett, S.T. and Crowley G.M. (2000) Action Plan for Australian Birds 2000 – Recovery Outline, Australasian Bittern] Stephen T. Garnett - Queensland Parks and Wildlife Service, and Gabriel M. Crowley - Birds Australia, Environment Australia, 2000,ISBN 0 6425 4683 5
IUCN (2009) IUCN Red List of Threatened Species. Version 3.1 – Australasian Bittern , (Accessed 22 February 2017).
NPW Act (1972) National Parks and Wildlife Act 1972—21.10.2011 South Australia, Schedule 8 Vulnerable species (accessed 10 March 2014)
SAC (1997) Final Recommendation on a nomination for listing: Australasian Bittern (Botaurus poiciloptilus) (Nomination No. 425). Scientific Advisory Committee, Flora and Fauna Guarantee. Department of Sustainability and Environment: Melbourne.
TSC Act (1995) Threatened Species Conservation Act 1995, New South Wales, Schedule 1. (Accessed 22 February 2017) Threatened Species Conservation Act 1995
TSP Act (1995) Threatened Species Protection Act 1995, Tasmania, Threatened species list
WC Act (1950) Wildlife Conservation Act 1950, Western Australia, Wildlife Conservation Act (SpeciallyProtected Fauna) Notice 2008(2). Schedule 1 — Fauna that is rare or is likely to become extinct, Government Gazette 5 August 2008.
See also other sites on this species
Birds in Backyards - Australian Museum. 2008.
Australasian Bittern Survey (survey forms, calls and information) - Birdlife Australia.
Species profile and Threats Database - Australasian Bittern - Department of Environment & Energy, Australia.
Species Profile and projects – Australian Bittern - Department of Environment and Conservation, New South Wales.
Please contribute information regarding the Australasian Bittern - observations, images or projects.