The Powerful Owl: a stealthy top predator or a fancy umbrella for Hunter Valley forests?

This article is a special contribution from guest author Hayley Averell. If you’ve seen these birds in your back yard add your comments below because we’d love to hear about them. They are magnificent birds.

The Powerful owl. Could it be an umbrella? (Image: Greg Sharkey CC)

Australasia’s largest owl is found right on my doorstep, in the beautiful Hunter Valley and Lake Macquarie region of New South Wales. The Powerful Owl, Ninox strenua, is a stealthy top predator, and more imposing than any of the common nocturnal birds you find in backyards. Living along the east coast of Australia, the Powerful Owl is nationally listed as Least concern, meaning it is considered a secure species, but in New South Wales and Queensland is listed as Vulnerable.

Scientific knowledge about the powerful owl is young and incomplete, but growing; and the future abundance of powerful owls depends on the growth of this scientific knowledge. So what do ecologists know about the powerful owl? What actions are needed to conserve these elusive predators?

What is a Powerful Owl?

It’s Australia’s largest owl measuring up to 60cm from head to tail, and its wings can span 140cm at full stretch. Powerful owls have dazzling yellow eyes, with a dark brown/grey body colouration, and while it usually remains quiet, you may be lucky enough to hear a typical “owl-like” hoot; a bellowing “WHOO HOO”. I can only hope of spying or hearing an individual one day.

Being reclusive and nocturnal, their ecology has been a mystery until recently. From the 1990’s onwards however, lots of ecological research has been done, for example, tracking their home ranges, determining their preferred diets and identifying the major threats to the species.

The reclusive Powerful Owl may be watching you while you walk through Mount Cootha. (Image: Aviceda CC Wikipedia

Powerful owls mainly eat small arboreal (tree-living) mammals and marsupials, like the ring-tailed possum. Powerful owls hunt these animals over home ranges as large as 1,000 hectares. Dr Raylene Cooke of Deakin University discovered that powerful owls may eat anywhere from 250-350 possums every year. That’s about 5 possums a week, which is why they need such a large area of healthy productive forest!

Possums and the other arboreal prey of the powerful owl depend on productive old growth forests for food and shelter. Because the powerful owl is a top carnivore, it depends on a healthy and substantial supply of prey, which in turn, depend on a large and healthy ecosystem. The powerful owl is a classic umbrella species, meaning, to conserve it you have to conserve many other plants and animals. Both the owl and its arboreal prey depend on the health and preservation of old-growth forest ecosystems. The conservation of the powerful owl depends on the ability of forest managers to conserve everything the owl depends upon. Not only must the owl’s prey be conserved, but indirectly it depends on the conservation of its prey’s habitat and their food sources. The old-growth forest species and many species that live there fall under the powerful owl’s umbrella.

The ideal habitat for the powerful owl provides old, hollow-bearing trees in an open forest or woodland environment. Old growth forests along the east coast, for example the Watagans and Jilliby State Conservation areas, provide this habitat.

Tree hollows provide roosting habitat for the powerful owl, but also, are vital shelter for the arboreal mammals the owl hunts. Large and mature trees with suitable large hollows (greater than 50cm diameter), are the trees that are primarily logged. Clearing of old-growth therefore not only impacts on powerful owls, but also their arboreal prey; a double whammy.

As well as removing important trees logging and clearing breaks up or fragments this vital habitat. Not only does forest fragmentation decrease the available habitat for the owl’s prey, fragmentation can also alter the characteristics of the remaining habitat for these animals. Research done by Soderquist and Gibbons (2007) suggested that this fragmentation was causing the powerful owl to travel further for hunting and exert more energy in the process.

Management: to monitor and conserve.

Given the elusive nature of the powerful owl, what should be done to best protect the species? The 2006 ‘NSW Recovery Plan for the Large Forest Owls’ addresses this question (released by the NSW Department of Environment and Conservation, DECC).

The recovery plan recommends actions for monitoring the species and promoting its conservation and recovery. The plan has been implemented over a period of five years, to safeguard populations of powerful owls where they occur. One of the most important actions for the species is to conserve our precious old-growth remnant forests, for the ecological viability of powerful owls, and the multitudes of other forest-dwelling biota as well.

Scientific knowledge about the powerful owl and its ecology is young and growing. Continued monitoring of the powerful owl collects vital data for future forest management decisions, and provides important information about the numbers of breeding pairs, their nest sites and the success of breeding seasons.

Effective conservation of many top order predators requires the conservation of the ecosystem they live in. Like an umbrella covers those gathered under it, properly conserving top order predators like the powerful owl, often encompasses the conservation of whole ecosystems.

Some other interesting links

Listen to the Powerful Owl here.

And some more reading for you here.

The Birsbane City Councils Large Forest Owl Conservation Plan