National Wetlands Update February 2013
Issue No. 22, February 2013
The Australasian bittern and its water requirements
Robyn Pickering, BirdLife Australia
Australasian bittern flying above a different type of foraging habitat in Kulinilup Nature Reserve, October 2008.
New knowledge about the water and plant life requirements of the Australasian bittern will help guide management of their wetland habitats.
The Australasian bittern (Botaurus poiciloptilus) is a large (66-67 centimetre), stocky, thick-necked heron with mottled buff and brown plumage. It generally occurs singly or in pairs, usually in beds or reeds, rushes or sedges in freshwater wetlands. In south-east Australia it also occurs in irrigated areas and rice fields. It is found in south-west and south-east Australia and New Zealand.
The Australasian bittern is dependent on vegetated freshwater wetlands and the decline of such wetlands throughout Australia over the last century has resulted in a significant decline in the species. The vegetated wetlands it inhabits are usually shallow wetlands which are more likely to be significantly degraded by changes or developments than deeper wetlands.
There has been a variety of reasons that wetlands suitable for Australasian bittern have declined. These include:
- wetland salinisation
- wetland acidification
- reduced inflow due to changes in drainage and climate, drought, diversion for irrigation or water extraction, and
- wetland infill for urban or industrial development.
Typical bittern habitat at Kulinilup Nature Reserve, March 2012.
In recognition of these declines, and the estimated current population in Australia of only 250 to 800 adult bittern, the species was listed by the Australian Government as endangered in March 2011. It is also listed as endangered internationally in the IUCN Red List.
Since 2007 BirdLife Australia (formally Birds Australia and Bird Observation and Conservation Australia) and other organisations have been working hard to learn more about the Australasian bittern in order to improve its conservation status through the Bittern Project .
Data collected to date and scientific literature indicate that bitterns need shallow water less than 30 centimetres deep with medium to low density reeds, grasses or shrubs for foraging. However, the bittern needs deeper water with medium to high density reeds, rushes or sedges for nesting. These quite different water and habitat requirements further limit the availability of suitable wetlands for this endangered species. Wetlands providing habitat for Australasian bittern need to be given a high level of protection and provided with best practice management in order to conserve the species and other wetland fauna.