Look up! A powerful owl could be sleeping in your backyard after a night surveying kilometres of territory

Nick Bradsworth, Deakin University; John White, Deakin University, and Raylene Cooke, Deakin University

Picture this: you’re in your backyard gardening when you get that strange, ominous feeling of being watched. You find a grey oval-shaped ball about the size of a thumb, filled with bones and fur — a pellet, or “owl vomit”.

You look up and see the bright “surprised” eyes of a powerful owl staring back at you, with half a possum in its talons.

This may be becoming a familiar story for many Australians. We strapped tracking devices to 20 powerful owls in Melbourne for our new research, and learned these apex predators are increasingly choosing to sleep in urban areas, from backyard trees to city parks.

These respite areas are critical for species to survive in challenging urban environments because, just like for humans, rest is an essential behaviour to conserve energy for the day (or night) ahead.

Our research highlights the importance of trees on both public and private land for wild animals. Without an understanding of where urban wildlife rests, we risk damaging these urban habitats with encroaching development.

One owl, one year, 300 possums

Powerful owls are Australia’s largest, measuring 65 centimetres from head to tail and weighing a hefty 1.6 kilograms. They’re found in Australia’s eastern states, except for Tasmania.

Powerful owl with half a common ringtail possum — Powerful owl at roost with half a common ringtail possum (probably saving it for later).
Nick Bradsworth

These owls have traditionally been thought to live only in large old-growth forested areas. However, Victoria has lost over 65% of forest cover since European settlement, and because of this habitat loss, the owls are listed as threatened in Victoria.

Their remaining habitat is extremely fragmented. This means we’re finding owls in interesting places — from dry, open woodland to our major east coast cities. This is likely due to the high numbers of prey, such as possums, that thrive alongside exotic garden trees and house roofs.

Powerful owls usually eat one possum per night, or 250-300 possums per year — mostly common ringtail and brushtail possums in Melbourne. They’re often seen holding prey at their roosting spots, where they’ll finish eating in the evening for breakfast.

This has ecosystem-wide benefits, as powerful owls can help keep overabundant possums in check. Too many possums can strip away vegetation, causing it to die back, which stops other wildlife from nesting or finding shelter.

Tracking their nocturnal haunts

But powerful owls are extremely elusive. With low populations, locating owls and researching their requirements is very difficult.

So, to help narrow down the general areas where powerful owls live in Melbourne, we used species distribution models and sought help from land management agencies and citizen scientists.

Over five years, we deployed GPS devices on 20 Melburnian owls to find how they use urban environments. These devices automatically record where the owls move at night and rest during the day.

We learned they fly, on average, 4.4 kilometers per night through golf courses, farms, reserves and backyards looking for dinner and defending their territory. One owl along the Mornington Peninsula travelled 47 km over two nights (possibly in search of a mate). Another urban owl called several golf courses in the Melbourne suburb of Alphington home.

Choosing where to sleep

After their nightly adventures, the owls usually return to a number of regular roosting (resting) spots, sometimes on the exact same branch. The powerful owl chooses roosts that protect them against being mobbed by aggressive daytime birds, such as the noisy miner and pied currawong.

A powerful owl showing defensive behaviour towards nearby pied currawongs trying to mob it.

We found the owls used 32 different tree species to roost in: 23 were native, and nine were exotic, including pine and willow trees. This shows powerful owls can adapt to use a range of species to fit their roosting requirements, such as thick foliage to hide in during the day.

Owls will generally roost in damp, dark areas during summer, and in open roosts in full or dappled sunlight during winter to help regulate their body temperature.

Our research also shows rivers in urban environments are just as important as trees for roosting habitat.

Rivers are naturally home to a diverse range of wildlife. Using trees near rivers to rest in may be a strategic decision to reduce time and energy when travelling at night to find other resources, such as prey, mates and nests.

Rivers that constantly flow, such as the Yarra River, are a particular favourite for the owls.

A powerful owl surrounded by leaves — Powerful owl at roost among dense *Kunzea* vegetation.
Nick Bradsworth

The urban roost risk

These resting habitats, however, are under constant pressure by urban expansion and agriculture. Suitable roosting habitat is either removed, or degraded in quality and converted to housing, roads, grass cover or bare soil.

We found potentially suitable roosting habitat in Melbourne is extremely fragmented, covering just 10% of the landscape because owls are very selective about where they sleep.

Although there might be the odd suitable patch (or tree) to roost in urban environments, what’s often lacking is natural connectivity between patches. While owls are nocturnal, they still need places to rest in the night before they settle down in another spot to sleep for the day.

A pair of powerful owls with beady eyes sitting at their roost — The classic ‘surprised’ powerful owl expression at a roost.
Nick Bradsworth

Supplementing habitat with more trees on private property and enhancing the quality of habitat along river systems may encourage owls to roost in other areas of Melbourne.

Powerful owls don’t discriminate between private land and reserves for roosting. So conserving and enhancing resting habitats on public and private land will enable urban wildlife to persist alongside expanding and intensifying urbanisation.

So what can you do to help?

If you want powerful owls to roost in your backyard, visit your local indigenous nursery and ask about trees local to your area.

Several favourite roost trees in Melbourne include many Eucalyptus species and wattles. If you don’t have the space for a large tree, they will also roost in the shorter, dense Kunzea and swamp paperbark (Melaleuca ericifolia).

Planting them will provide additional habitat and, if you are lucky, your neighbourhood owls may even decide to settle in for the day and have a snooze.

Nick Bradsworth, PhD Candidate, Deakin University; John White, Associate Professor in Wildlife and Conservation Biology, Deakin University, and Raylene Cooke, Associate Professor, Deakin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Urban owls are losing their homes. So we’re 3D printing them new ones

Dan Parker, University of Melbourne; Bronwyn Isaac, Monash University; Kylie Soanes, University of Melbourne; Nick Bradsworth, Deakin University; Stanislav Roudavski, University of Melbourne, and Therésa Jones, University of Melbourne

Native to southeastern Australia, the powerful owl (Ninox strenua) is threatened and facing the prospect of homelessness.

These birds don’t make nests – they use large hollows in old, tall trees. But humans have been removing such trees in the bush and in cities, despite their ecological value.

Owls are lured into cities by abundant prey, with each bird capturing hundreds of possums per year. But with nowhere to nest, they struggle to breed and their population is at risk of declining even further.

Existing artificial nest designs include nesting boxes and carved logs.
Author provided

Conservationists tried to solve this problem by installing nesting boxes, but to no avail. A 2011 study in Victoria showed a pair of owls once used such a box, but only one of their two chicks survived. This is the only recorded instance of powerful-owl breeding in an artificial structure.

So as a team of designers and ecologists we’re finding a way to make artificial nests in urban areas more appealing to powerful owls. Surprisingly, the answer lies in termite mounds, augmented reality and 3D printing.

Bring in the designers

Nesting boxes aren’t very successful for many species. For example, many boxes installed along expanded highways fail to attract animals such as the squirrel glider, the superb parrot and the brown treecreeper. They also tend to disintegrate and become unusable after only a few years.

What’s more, flaws in their design can lead to overheating, death from toxic fumes such as marine-plywood vapours, or babies unable to grow.

Designers and architects often use computer modelling to mimic nature in building designs, such as Beijing’s bird’s nest stadium.

But to use these skills to help wildlife, we need to understand what they want in a home. And for powerful owls, this means thinking outside the box.

What powerful owls need

At a minimum, owl nests must provide enough space to support a mother and two chicks, shelter the inhabitants from rain and heat, and have rough internal surfaces for scratching and climbing.

Traditionally, owls would find all such comforts in large, old, hollow-bearing trees, such as swamp or manna gums at least 150 years old. But a picture from Sydney photographer Ofer Levy, which showed an owl nesting in a tree-bound termite mound, made us realise there was another way.

Owls have been observed using termite mounds in trees for nesting.
Blantyre, Author provided

Termite mounds in trees are oddly shaped, but they meet all necessary characteristics for successful breeding. This precedent suggests younger, healthier and more common trees can become potential nesting sites.

A high-tech home

To design and create each termite-inspired nest, we first use lasers to model the shape of the target tree. A computer algorithm generates the structure fitting the owls’ requirements. Then, we divide the structure into interlocking blocks that can be conveniently manufactured.

Trees and their surroundings can be scanned by lasers for precise fitting.
Author provided

To assemble the nests, we use augmented-reality headsets, overlaying images of digital models onto physical objects. It sounds like science-fiction, but holographic construction with augmented reality has become an efficient way to create new structures.

So far, we’ve used 3D-printed wood to build one nest at the University of Melbourne’s System Garden. Two more nests made from hemp concrete are on the trees in the city of Knox, near the Dandenong Ranges. And we’re exploring other materials such as earth or fungus.

These materials can be moulded to a unique fit, and as they’re lightweight, we can easily fix them onto trees.

With augmented reality, it is easy to know where to place each block. Right: Views from the augmented reality headset.
Author provided

So is it working?

We are still collecting and analysing the data, but early results are promising. Our nests have important advantages over both traditional nesting boxes and carved logs.

This is, in part, because our artificial nests maintain more stable internal temperatures than nesting boxes and are considerably easier to make and install than carved logs. In other words, our designs already look like a good alternative.

And while it’s too early to say if they’ll attract owls, our nests have already been visited or occupied by other animals, such as rainbow lorikeets.

Future homes for animal clients

Imagine an ecologist, a park manager or even a local resident who wants to boost local biodiversity. In the not-too-distant future, they might select a target species and a suitable tree from an online database. An algorithm could customise their choice of an artificial-nest design to fit the target tree. Remote machines would manufacture the parts and the end user would put the structure together.

Nests from 3D printed wood are easy to install.
Author provided

Such workflows are already being used in a variety of fields, such as the custom jewellery production and the preparation of dental crowns. It allows informed and automated reuse of scientific and technical knowledge, making advanced designs significantly more accessible.

Our techniques could be used to ease the housing crisis for a wide range of other sites and species, from fire-affected animals to critically endangered wildlife such as the swift parrot or Leadbeater’s possum.

Dan Parker, PhD Candidate, University of Melbourne; Bronwyn Isaac, Lecturer, Monash University; Kylie Soanes, Postdoctoral Fellow, School of Ecosystem and Forest Sciences, University of Melbourne; Nick Bradsworth, PhD Candidate, Deakin University; Stanislav Roudavski, Senior Lecturer in Digital Architectural Design, University of Melbourne, and Therésa Jones, Associate Professor in Evolution and Behaviour, University of Melbourne