The Living Murray-Intervention Monitoring: Australasian Bittern and Australian Little Bittern presence and breeding surveys, 2021-22: Intervention monitoring in Barmah-Millewa Forest 2021

The Living Murray Program is jointly funded by state and federal governments coordinated by the Murray-Darling Basin Authority. Environmental watering is delivered to six ‘icon’ wetlands along the Murray-Darling Basin. The Living Murray Program delivers ecological monitoring programs at each icon site to understand the wetland health outcomes of the watering. One of the six icon sites chosen for its environmental, cultural and international significance is the Barmah-Millewa Forest. Based on previous annual monitoring results, Barmah-Millewa Forest is known to support approximately 30% of the known Australasian Bittern population. This report summarises the outcomes of the 2021/2022 monitoring of this endangered species in this context.
In November and December 2021, two triangulation surveys were conducted to estimate the number of calling males. A La Niña weather cycle resulted in extensive rain and flooding, providing vegetation density and structure, and high-water levels optimal for bittern breeding. Although not all the regular survey sites were accessible, our results indicate an abundance exceeding previous years surveys with 78 male Australasian Bitterns and 41 Australian Little Bittern detected.
Consistent future environmental water flows are critical to the protection of the Australasian and Australian Little Bittern populations in the Barmah-Millewa Forest; this site being the most important in Australia for the species. Invasive species management and exclusion is recommended to prevent further damage to wetland substrate from pugging, protect reed bed densities, minimise predation by foxes and feral cats, and prevent further weed infestations.
This marks the seventh year of The Living Murray program’s Australasian and Australian Little Bittern presence and breeding surveys in the Barmah-Millewa Forest. The acoustic triangulation survey has been applied each year. Although providing a repeatable methodology, our findings suggest that it is an unreliable metric to sufficiently describe the status of Australasian and Australian Little Bittern at the Barmah-Millewa Forest. The variability in Australasian Bittern call frequency suggests that the results from the triangulation method significantly under-estimate the abundance. We recommend incorporating an acoustic monitoring protocol into future surveys.