Images courtesy of WWF Australia.
Endemic to the forests of south-eastern Australia and found from mid-Queensland to Adelaide in South Australia, the native Grey-headed Flying-fox (GHFF) is beneficial to the environment and listed as vulnerable.
Grey-headed Flying-foxes roost communally during the day in groups that can number in the tens of thousands. Historically, the only known permanent roost in Victoria was in far East Gippsland. In the mid 1980’s a new camp formed in the Royal Botanic Gardens Melbourne, and this was relocated to Yarra Bend in 2003. Since then, more than 20 permanent and seasonal camps have formed across Victoria, including Geelong, and throughout Gippsland, central and western Victoria. In 2010a colony became established in Rosalind Park, and this Bendigo-based permanent colony is nationally significant for its size and as a maternity camp for breeding and birth of young.
Located in the centre of Bendigo, Rosalind Park is a significant site for its historic trees, buildings, structures and landscape reflective of Bendigo’s character and horticultural history. Many trees date back to the 1800s and new ones are planted each year including elms, oaks, Queensland kauri and Australian teak.
The number of GHFF in Rosalind Park varies seasonally each year with between 2000 and 30,000 calling Bendigo home. The flying-foxes affect the tree branches they are roosting on through damage from their claws and breakage due to their combined weight. A proportion of trees in the park are impacted by GHFF and showing varying levels of damage, with the most affected in the park’s historic fernery area.
GHFF are susceptible and undergo heat stress when temperatures exceed 40 degrees C, with high rates of mortality experienced on extremely hot days. The current response on such days is direct intervention by the Victorian Department of Land, Water Environment, and Planning with assistance from the City of Greater Bendigo and wildlife carers to spray bats with water from hand-held sprayers to cool and hydrate them as well as to take dehydrated bats into care for rehabilitation.
Acknowledging the level of damage was reducing the useful life expectancy and survival rate of the trees, the City instigated a trial of artificial roosting structures within the fernery of Rosalind Park to relieve pressure on the trees and improve tree health. The City are also investigating and testing a trial atmospheric cooling system consisting of sprinklers within the tree canopy to cool the bats and restore humidity in the fernery and to protect the mid-storey plants. This will also reduce the need for human intervention on days of extreme heat.
To undertake the trial, the City of Greater Bendigo has asked WSP to assist in the planning, design, installation and evaluation of both an artificial roost and an atmospheric cooling system for the GHFF roosting in Rosalind Park.
Trialled for the first time in January 2021 when summer temperatures climbed as high as 41 degrees C, data logging devices show the temperature in the test zone dropped by up to two degrees. The heat stress index also dropped, and no flying-fox deaths were recorded. In the summer of 2019/2020, up to 220 flying-foxes died in Rosalind Park from heat stress.
As well as aiming to improve animal welfare outcomes, protecting and enhancing canopy cover, tree health and survival, the trial is looking at solutions to reduce the need for and extent of human intervention during extreme heat events. Post the trial, WSP will undertake a scientifically robust evaluation and report to enable evidence-based decisions by the City and other camp managers facing similar challenges across Australia.
Click here for more information on our grey-headed flying-fox project.
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