The Australasian bittern (Botaurus poiciloptilus) is an iconic waterbird colloquially known as the Bunyip bird, due to its deep booming, nocturnal call. Sadly, the Australasian bittern is endangered, and it is estimated that only 1,300 individuals remain. Loss of wetland habitat and changing water regimes are key threats to this species.

Australasian bitterns favour large wetlands that provide sufficient coverage, such as reed beds, rushes, and sedges, and prefer to breed in dense stands of emergent wetland vegetation. Hence, the wetlands of the Lower Murrumbidgee Floodplain make ideal habitat for these birds. In southern NSW, bitterns have also been observed using rice crops within irrigation areas (see Matt Herring’s ‘Bittern in Rice Project’). The Commonwealth Environmental Water Holder (CEWH) and their partners deliver water to support bittern breeding.

An elusive and well-camouflaged bird, the Australasian bittern is often difficult to detect amongst its preferred vegetation of reeds, rushes, and rice. Fortunately, when males are in search of a mate, they have a distinctive “booming” call which can resonate for more than a kilometre across a quiet wetland. Consequently, they are more often heard than seen. This provides an opportunity for researchers to gain insight into population and breeding activity, as well as an understanding of the watering needs of this species.

The endangered Australasian bittern. Source Bittern in Rice Project; Matt Herring.

Research funded by the CEWH is investigating the relationship between the timing and duration of water for the environment deliveries and bittern calling activity. This information will assist in evaluating their response to environmental watering actions.

Charles Sturt University researcher, Dr Elizabeth Znidersic, is leading the project in collaboration with Dr Helen Waudby (NSW Save our Species program). This project is utilising previously deployed automated call recorders and depth loggers from key Lower Murrumbidgee Monitoring, Evaluation and Research (MER) wetland sites.

Call recorder units and loggers have been collecting audio and wetland hydrological data since 2016 from these wetlands, where Australasian bitterns are known or expected to reside. This means that calling activity in response to water depth and temperature, can be evaluated for the last seven years.

Dr Znidersic has developed a call recognition model which identifies Australasian bittern calls. This supports efficient analysis and interpretation of the large audio datasets produced.

“The challenge of detecting Australasian Bitterns is a result of their irregular calling pattern and that they call mostly in the hours of darkness. This means we need to record continuous audio data to increase the detection probability which can amount to years of listening! Therefore, we use an automated computer analysis technique to detect the Australasian bittern calls”, said Dr Znidersic.

The outcomes of this research are imperative for developing recommendations for delivery of water for the environment to support bittern breeding in the Murrumbidgee. It will also contribute to the development of guidelines for water managers, specifying the ideal environmental watering regimes (timing, duration, depth, and volume) necessary to stimulate successful breeding and survival of Australasian bitterns.