How do our possum assassins use urban landscapes?

the eyes of a possum assassin

An urban living possum assassin (AKA powerful owl).

We are incredibly lucky to have a native apex predator haunting our urban landscapes.  The powerful owl (Ninox strenua) is known to live in restricted areas of Melbourne, Sydney and Brisbane. They silently travel around dropping in on unsuspecting possums and gliders, and feasting on them.  It is not uncommon to encounter an owl with the decapitated corpse of a possum in its talons.

Enough with the gore! What do we know about these amazing predators in our urban environments?  We know they are not very common in urban environments, and large areas of our cities are completely unsuitable for them due to loss of vegetation associated with urbanisation (Click here to check out some models of habitat for powerful owls in Melbourne).  We also know there is plenty of food for them in our cities, but their capacity to breed is probably limited by a lack of large tree hollows (Another paper that may interest you on urban ecological traps for powerful owls).

Ok, so what don’t we know?  Well we really don’t know too much about how powerful owls use the urban landscape. How far do they travel? Do they go deep into the suburbs or do they stay in the more wooded parks? How much space does an owl actually need to survive in a city? How can we better manage our urban landscapes to facilitate the expansion of powerful owl populations? Hence our new research project to track urban powerful owls in Melbourne.  This research is part of our Deakin honours student’s (Nick’s) project. A parallel project will be aiming to do the same thing in Sydney, so we can compare and contrast two different cities.

So last night was our first night of trying to catch a powerful owl to put on a GPS logging device and attached radio transmitter. I will say it is not easy to catch owls, and we have done it a fair bit so have a few little tricks we have learned along the way.  As luck would happen we caught one! First attempt! There is no way we will be maintaining that average!

A happy honours student

Deakin honours student Nick with the first powerful owl of his research project. I think he looks kind of happy.


Imagine sitting in the dark, nets up in the canopy, knowing there is an owl close by. It is exciting, and scary at the same time.  The owl never called, it just quietly cruised around where we were. So last night the owl came into the net.  We were lucky, and this launched us into a flurry of activity and fitting of trackers etc.

How do you attach a tracking device to an owl? We used a tail mounting approach, where the device is fixed to the two central tail feathers. It is a useful approach as the tail feathers will eventually naturally moult and the device will fall off the animal.  Also, the device sits very nicely to not impede its flight. Finally, the feathers of the back and wings cover the device up so you cant see it.

Tail mounted transmitter

The GPS/radio tracking device fitted to the tail feathers of our powerful owl.  Note: all the other tail and back feathers are being held out of the way to show it to you.

So after fitting our tracker to the owl, we gave it a final check to make sure both the owl and the device were fine.  Nick held the owl up in the air, and whoosh, it was gone.  It flew really well up to a nearby tree. I might of imagined it, but I am sure it gave us a dirty look before heading off through the trees.

Nick releasing powerful owl

And Whoosh off it goes! Nick releasing the first powerful owl carrying a GPS tracker.

Powerful owl after release

The owl just after release perching briefly on a branch.  Note you can just see the tip of the aerial at the end of the tail, and the tracker is held nicely under the feathers.

We checked the owl a couple of times last night and again this morning.  It is doing really well.  This morning it was roosting with another adult powerful owl some 500 metres away from where we caught it.  The GPS recording where it goes when we are not watching it.  Technology has come a long way, and with every technological advance comes opportunities for us to understand our wildlife better. This owl may be able to help us design urban landscapes better to suit the needs of our wildlife.

Me with a powerful owl

Me with the owl. It really doesn’t look all that big, but this owl was just over 1.5 kg!

It’s time for an urban revolution! It’s time to take back our streetscapes.

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A tawny frogmouth pair sitting in an urban streetscape tree in Melbourne.

Other than houses and roads, one of the things that are most visible to people in our urban environments are the streetscapes. The foot print of streetscapes throughout our urban areas is enormous yet their potential for great biodiversity outcomes largely goes unrealized. In fact we generally manage them in a fashion that creates an ecological desert (maybe a little poetic license) with extremely limited value for biodiversity.

Many years ago we investigated the role of different streetscape vegetation and the response of birds to it (You can read more here). Surprise, surprise, native bird diversity was highest in streetscapes dominated by native trees. Probably more concerning was the fact that 75% of the bird abundance in streetscapes dominated by exotic trees was made up by a few species introduced to Australia! Upshot, streetscapes dominated by lawns and exotic trees are not good for birds, and presumably native biodiversity as well.

Interestingly, in Australia, we refer to streetscapes as nature strips. Whilst this may make us feel better about our impact on the environment, it is a grossly incorrect term. In reality, as far as nature is concerned, streetscapes sit on a continuum from ecological desert to nature strip. So just calling it a nature strip does not make it a nature strip.

So here comes the revolution bit. What can we do about it? This is actually a tough one. I used to give lots of talks to local government about turning streetscapes into nature strips. Obviously step one is pushing for native tree species to be used throughout our urban areas rather than the exotic European species favoured by many urban designers. I was often surprised to find a backlash to this on various different levels e.g. “Native trees do not have the great form that exotic trees have”, “Native trees drop limbs and leak sap”, through to “This will impact upon the value of the houses”. This last point a reference to houses in areas with established exotic trees having higher value. Probably correlative rather than causative.

I usually took my recommendations a step further and encouraged councils to consider ripping up the lawns and replacing them with native vegetation. Ultimately, suggesting the idea of introducing structural diversity to the planting. This usually got many and various different responses, it must be noted not always negative. The main negative, other than the negative aesthetic influence, was the issue of public safety. In essence with structure on the streetscapes the public have no line of sight and as such perception of risk and safety is influenced. I actually think this is a valid point that we need to think about.

Personally, I think we need to take control of our streetscapes, and I think we need to have a revolution that forces local governments to act in favour of nature rather than against it. We need to fight for a diversity of native canopy trees to be the dominant vegetation on all of our streets. Following this, we need to rip up the lawns. Replacing the mown and managed grass with diverse low growing (less than a metre) native vegetation will have enormous benefits for native biodiversity. If everyone in a street did this, would councils force them to change it back? Who knows, but it would make for an interesting situation.

moth 3

A native heliotrope moth. Elevated richness of native invertebrates will result from turning streetscapes into nature strips.

Finally, coming back to the point about structural plantings and safety. I do agree with the issue around perception of safety, so how do we deal with it. Actually this is somewhat more straight forward than one would think. We can get structure into our urban environments by thinking of our streetscapes and our front gardens as part of the same system. Spatially they are only a few metres from each other. So use the streetscape to enhance the canopy and low growing vegetation, and utilise your front garden to add a bit of mid-storey structure to the system.

Imagine your own street. Imagine being immersed in an urban woodland. Imagine walking through it to the sound of native Australian birds, and watching the bees and butterfly’s etc. Would that elevate your perception of wellbeing? Research suggests it would. Would it feel cooler in the summer? Again, research suggests it would. Ultimately, imagine your entire city dominated by streets like this. What are you waiting for? It is time for an urban revolution.