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Powerful owls

In April, forests along Australia's south-east are full of the love hungry hoots of our largest owl - the powerful owl. These champion hunters are now getting ready to settle down and make babies.

The Powerful Owl, Ninox strenua, is Australia's largest and most powerful owl. It's also the only owl in Australia that hoots like the owls in children's books - "whoo hoo" - rather than screeching like a barn owl.

From March to April, Powerful Owls start hooting more frequently. The male is the one making most of the ruckus, calling to tell other owl pairs that this is his territory.

"They are basically saying this is our patch, buzz off," said Dr Rod Kavanagh, principal research scientist, NSW Department of Primary Industries.

By May, the owls quieten down as the time to nest approaches. Throughout June and July they still call softly to each other as the female starts to roost in the nest.

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I love woo

Powerful Owl pairs occupy large areas. When they start to court in March the owls move closer together, roosting on the same tree and then the same branch.

They make their nests in trees with a large hollow, preferably a eucalypt over 200 years old. Like all of the Ninox family, Powerful Owls are winter breeders, nesting in late May to early June. Almost like clockwork, the female enters her nest hollow at the same time each year.

The female Powerful Owl lays an almost spherical, dull white egg around four to five centimetres in diameter, usually laying another after a gap of a few days. She incubates the eggs for 35 to 38 days, and will spend another 30 days with the chicks before she's free to leave the nest and hunt for herself.

During this time the male roosts nearby, keeping an eye on his family as the female incubates the eggs and the chicks grow and mature. Throughout this period he is solely responsible for the family's food.

"The males do the lion's share of the work for three months," said Kavanagh.

The chicks begin to fledge in September. The older chick (from the first laid egg) will leave the nest first. From September until December it's a great time to look for Powerful Owls, as the whole family can be seen roosting close together. The fledglings (juveniles) are strikingly different from the adults, with soft white plumage with dark streaks and eye patches like a mask. They lose this plumage at about four to five months.

Unlike the adults hoot, juveniles make a loud trilling noise when begging for food.

Fact file: When: Now is the time to listen for these remarkable birds as they begin their fairytale romance. Where: The Powerful Owl is found north as far as Rockhampton and Mackay and south and west as far as the Victoria/South Australia border. Other info: Listen for a series of hoots sounding like: 'Whoo! Hooo' [Listen to the male and female calls above] There are nine different owls in Australia of two distinct types. The Ninox, including the Powerful Owl, are hawk owls, the Titos are the masked owls. Also called the Eagle Owl, Powerful Owls are the largest of all Australian owls. Males grow to 65 centimetres in height and weigh up to 1.7 kilograms. The female at 54 centimetres and 1.6 kilograms is slightly smaller, and has a slightly softer, higher call than the male. Unusually for birds of prey the males are bigger than the females with a broader head and chest. Their wingspan can be an astounding 135 centimetres - not quite as wide as an average human is tall. Both males and females are dark brownish grey with well bright yellow eyes.

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I love woo not?

Like many other birds, Powerful Owls are reputed to mate for life.

To test if this is really true, Fiona Hogan PhD student at Deakin University in Melbourne has been collecting feathers from Powerful Owls over the last three years.

Hogan is sampling DNA from the shed feathers from roost trees. She has also collected blood feathers from chicks in order to do paternity tests. Her results will shed light on the monogamy of owls, as well as detect any genetic diversity between owls in Queensland versus owls in Victoria. So far, they're suggesting that Powerful Owls may not be as monogamous as we'd thought.

"I don't know if it is as straightforward as people think, as we have found that adults who lose a mate have replaced this mate by the following breeding season," said Hogan.

People have also reported females booting another female out of the nesting area, she said.

"It's hard to say 'yes' it's definitely the same male and female breeding each year" said Hogan.

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Fierce hunters

Powerful Owls are capable hunters and include sugar gliders, greater gliders, ringtail possums and brushtail possums in their diet. According to Dr Raylene Cooke from Deakin University, Powerful Owls eat an astounding 250 to 350 possums a year. Dr Cooke analysed 2500 owl pellets to determine this fact.

Unseen and unheard, the winged hunter swoops onto an unwary possum, grasping it with its claws and breaking its neck. In one great bite the Powerful Owl can eat a possum's head. The male will then take the headless possum back to the roost and eat some more, as well as provide meat for the female and two chicks.

Powerful Owls will also eat mice, insects and a range of other birds, including quite large prey such as white cockatoos, magpies, and even ravens.

They specialise in their diet, but eat a broad range of animals over their habitat area. Coastal Powerful Owls will favour Ringtail Possums, while in the high country they prefer Greater Gliders.

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A threatened lifestyle?

Like all hunters, Powerful Owls require large areas to hunt. In Victoria 65% of their habitat has been cleared and the remaining habitat is fragmented. They need a large hollow to breed in because of their large size - a fully grown female as well as two large chicks need to fit into the family home.

Despite this and although they are listed as vulnerable, Kavanagh said there may be more owls than previously thought, with records of thousands of owls spotted in New South Wales. Kavanagh and others think this may mean that the owls are more adaptable to different environments that previously thought, with owls even roosting in plantation pine forests.

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Other hawk owls

Further north, Rufous Owls Ninox rufa, take over from the Powerful Owl as the winged night hunter. Slightly smaller and lighter in colour, this rainforest bird takes large prey, like the Powerful Owl, with the dinner menu including gliders and flying foxes, brush turkeys, kookaburras and cockatoos.

Their call is similar to the Powerful Owl but softer and more nasal. They also call far less frequently, and are elusive though frequently aggressive to humans if their nesting area is disturbed.

As their name suggests, Barking Owls, Ninox connivens, have a call like a barking dog with two short barks preceded by a soft groaning sound. Smaller again than the Rufous Owl, they grow to only 35 to 40 cm in height, with a wingspan of about one metre. They are however aggressive hunters and will take a range of bird prey, including ducks, but will eat almost anything, and frequently in southern Australia make themselves popular by dining on rabbit.

They are found all around Australia apart from in the central west and south. Barking Owls call all year round.

One of the most common and familiar owls is the boobook, Ninox boobook. Found all over the continent, the little owl grows to a maximum of 36 centimetres in height. It has a soft hoot with the second note pitched lower than the first.

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Masked owls

Masked owls in Australia include Barn Owls, Masked Owls, Grass Owls and Sooty Owls. Listen out for screeches, whistles and screams from these owls. Barn Owls in particular can be found almost all over the world, and breed at any time of year.

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Further info and credits

The Owl Pages

The Southern boobook owl

Lamington National Park

Thanks to Rod Kavanagh for the owl calls, Fiona Hogan for the video and Phil Hansbro and Raylene Cooke.

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