A long-term project by Deakin University researchers has provided the most intimate picture yet of the daily habits of Melbourne's beloved Powerful Owls.
Using GPS tracking devices, researchers have been able to map the home ranges of these elusive and cryptic birds and the times of night they are most likely hunting or heading home to bed.
Nick Bradsworth, a PhD candidate in Deakin University's School of Life and Environmental Sciences, said the research team had tracked the movements of 23 owls in the Greater Melbourne area over the past four years and found that the amount of space suburban owls use is much smaller than those living in Victoria's forested areas.
"The home range for Powerful Owls in Melbourne is between 300ha and 500ha whereas owls living in rural and forested areas can have territories of up to 2000ha," Mr Bradsworth said.
During the study, Mr Bradsworth and the research team caught each owl and attached a lightweight GPS tracker to their tail feathers for 40 nights. The tracker was able to deliver data about the owl's movements from dusk until dawn which can't be gathered by other means.
"The GPS trackers allow us to see that the owls are busy at dusk, jumping short distances from tree to tree, telling us that this is their feeding time. As night progresses, their trips extend further as they guard their territory and at dawn they fly in long, single sweeps, as they head home to roost for the day.
"The long distance movements are often over parts of the landscape that owls would not routinely use, such as the impervious surfaces of roads and buildings. We believe this is why the owls travel over these areas quickly without stopping for rest.
"We've also found over the years that these owls are spending a lot of time in the evenings on private property. So it is important to protect not only parks, reserves and river systems, but also the bushland and canopy trees on private property," Mr Bradsworth said.
Powerful Owls are Australia's largest owls and have wingspans of up to 135cm. They will potentially mate for life and can produce up to two chicks a year during the winter breeding season. As apex predators, they eat large mammalian tree-dwelling prey, mainly common ringtail and common brushtail possums. They need dense vegetation to roost for the day, and large hollow-bearing trees to nest so are found mainly in Melbourne's leafy eastern suburbs along the creek systems, especially the Yarra River and Dandenong Creek.
But while food is plentiful, a lack of suitable nesting sites is impacting on their ability to breed. Powerful Owls breed in the hollows of large eucalypts and the trees need to be at least 150 years old to have a large enough hollow or cavity to accommodate an owl family.
Associate Professor Raylene Cooke from Deakin's School of Life and Environmental Science and the project's lead researcher has investigated Melbourne's Powerful Owls for over 23 years.
"If they don't have a suitable hollow, the owls can't breed," Associate Professor Cooke said. "Our research has shown how this loss of large, old eucalypts in suburban areas has prevented them from breeding altogether in some urban parklands."
Mr Bradsworth said his research will continue to investigate how Powerful Owl movements are impacted by expanding urbanisation and whether genetic testing may shed light on where each new generation of Powerful Owls go when it is time to leave the natal territory and start raising their own families.
"Everyone can play a part in helping the Powerful Owl by retaining large old eucalypt trees in their backyards, or by planting indigenous native trees today," Mr Bradsworth said.
Powerful Owls are found residing in urban Melbourne, Sydney and Brisbane and sightings of this threatened species can be reported to BirdLife Australia: http://www.birdlife.org.au/projects/powerful-owl-project/melbourne-powerful-owl-project?projects/powerful-owl-project/melbourne-powerful-owl-project-pow
