Powerful owls have settled down in Melbourne’s suburbs, but it might not be for long

In the bushy suburb of Warrandyte on the outskirts of Melbourne, a small group of scientists are scouring a pine forest for evidence of Australia’s biggest owl — the powerful owl.

One scientist has his eyes locked on the highest branches, trying to spot an owl among the pine cones.

Others look for tell-tale splashes of white owl poo around the tree trunks, brown chevron-patterned feathers, and the grey lumps of fluff and bones that are their regurgitated pellets.

Powerful owls can be spotted throughout south-eastern Australia’s forests and woodlands, but some of them have made a home in suburbia.

Although they don’t spot any owls in the canopy, ecologist John White and PhD student Nick Bradsworth from Deakin University are convinced by the ground-level evidence that the birds are around here somewhere.

“We better get the net set up,” Mr Bradsworth says.

The plan is to catch an owl and attach a tracking device to it. This will help the scientists understand how these magnificent birds survive in a landscape fragmented by houses, roads and noisy humans.

Catching a predator
With its bone-crushing talons and huge yellow eyes, the powerful owl is a formidable predator.

And weighing in at around 1.5 kilograms, catching one isn’t easy.

Standing in a dried out drainage channel at the base of the pine forest, Dr White aims a bow and arrow at the highest branches of a nearby eucalypt.

“We do get some pretty weird looks when we walk into urban reserves with all this gear,” Mr Bradsworth says, “but John is actually firing fishing line into the canopy, which we will use to position the net.”

Once the net is in place between two trees it’s about 12 metres across and 8 metres high. A light breeze causes the middle to bulge out like a ship’s sail.

“We try to cover off the canopy as best as we can, because the owls move through the canopy to hunt for prey. So if we can get the net to that height they are unlikely to go over the top,” Mr Bradsworth says.

“The owls love to perch on some of these dead branches, so we will try to encourage them into the trees next to us first.”

The owls start to move from their roost around dusk, so the scientists have to attract their attention before they fly off to hunt for the night.

Powerful owls are very territorial. As soon as they’re kicked out of their parents’ territory as juveniles, they’re off to find a patch of their own — or pair up with an owl that’s already established a territory.

One way to encourage the owls toward the net is to make them think they have an intruder, which they will then come and investigate.

“We’ll play a sequence of owl calls for a while, alert them to our presence and then hopefully their first flight of the night is in our direction,” Dr White says.

They also play chick calls into the bush.

These owls mate for life, raising two chicks every year.

The last thing a pair of adults want is their one-year-old chicks from last year’s breeding season pestering them.

“The chicks are pretty demanding, flying around squealing at their parents trying to get some possum off them,” he said.

“They will actively chase their chicks away before they’ve turned one.”

As the ‘hoots’ and chick ‘trills’ travel up into the pine forest, the scientists can only watch and wait.

The chick call is suddenly echoed back to us. These chicks haven’t been kicked out by their parents just yet.

Then there is a distant, low hoot.

“Yep, it’s definitely an adult,” Mr Bradsworth says. Another soft hoot filters through the trees, and Dr White hears it too.

“It’s a male,” he says.

In a matter of minutes two looming shadows appear in trees on either side of the net — the resident adult pair are here.

“We’re playing the calls nice and quiet now because the owls are so close,” says Mr Bradsworth.

Finally, the female owl flies into the net. Mr Bradsworth runs forward to catch her before she hits the ground as the net is lowered.

The first job is to get a beanie over the owl’s head to calm her down and cover her enormous beak.

A small amount of whispered swearing follows as they try to untangle her huge talons from the net.

Once the owl is free of the net, Dr White positions himself in a camping chair and holds the owl out so Mr Bradsworth can attach the GPS tracker.

“No matter how many times you do this, it is intimidating holding one of these things,” says Dr White.

“They’re a huge bird.”

Mr Bradsworth finds her two longest central tail feathers, and glues the small tracking unit to the top of them.

An ecological trap
Powerful owls need three things to live in an area: a tree to roost in, a tree to nest in, and enough food to eat, according to wildlife ecologist Raylene Cooke from Deakin University, who leads the powerful owl research team.

Roost trees and food — mostly possums — are not a problem in Melbourne, but they require a nesting tree with a hollow that is at least one metre in depth to fit mum and two chicks, and that’s harder to come by.

“The only ones remaining are along our waterways and river banks.

“They are an essential element for powerful owls’ survival, so it’s really important we can maintain those trees as best as we can.”

And this is where the urban powerful owls can get into trouble — there just aren’t enough of those nesting trees.

“They pair up with a mate for life, so once they are holding down a territory it’s unlikely they will up and move to somewhere else just because there isn’t a suitable nesting tree,” Dr Cooke says.

“They’ve gone in thinking that they’ve got food and habitat, but then they can’t breed. It’s an ecological trap.”

The closest known breeding to Melbourne city is around 20 kilometres out, so while there are some birds roosting in some inner city parks they probably aren’t breeding.

Even when owls are breeding, the way they use the landscape means it might become harder for them to live an urban lifestyle, says Dr White.

“When we look at the tracks they make through the landscape, we know they use a few different patches of forest that are seemingly disconnected except for a thin strip of trees along river systems,” he says.

“And then they use those strips to join the dots between patches.”

If the green corridors contract more to make way for development, the owls may no longer be able to link the fragments of good habitat that remain.

“I suspect what will happen is the amount of habitat will start to dwindle to a point where they can’t connect up the bits, or it will drop below a threshold and they may well just naturally die out of those areas,” Dr White says.

“The minute the housing density gets too high, and the tree density drops away, the owls go.

Powerful wingbeats
Once they’ve heard the reassuring ‘beep beep’ of the radio transmitter component of the tracker, it’s time to release the owl.

The beanie is very slowly removed from her head — and she launches out of Mr Bradsworth’s hands.

For a moment the only sound is the air being thumped by her huge wings as flies to a nearby perch, and then Dr White chuckles, indicating he’s captured the perfect action shot of the release.

She stays in the tree for a while, picking at her feathers to realign them over the tracker.

“She’ll go off and forage for the rest of the night, and maybe meet up with the male again,” Mr Bradsworth says.

Source: https://www.abc.net.au/news/science/2019-05-11/powerful-owls-settle-in-melbourne-suburbs-but-maybe-not-for-long/11083064