Powerful Owls are Australia’s largest nocturnal bird of prey and also our largest hollow-nesting bird. They are a formidable predator, regularly taking prey up to their own body weight. Ringtail possums are a favourite but, depending on habitat, they also predate small and large glider species, brush tailed possums, sub-adult koalas, fruit bats, and a range of birds. Generally, these owls take arboreal prey but there are records of them occasionally taking small ground-dwelling mammals such as rabbits or small marsupials. Sadly, Powerful Owls are killed by secondary poisoning resulting from so-called “second generation” rodenticides, please don’t use these.
Many people camping in and around Halls Gap may have unknowingly heard a Powerful Owl calling, a deep “classic” hoot. But far fewer will ever have seen one. Listening at dusk for 10 minutes or so, the period when kookaburras are calling to just after they stop, is a good time to hear them. There are numerous recordings online that you can acquaint yourself with but please DO NOT play recordings to try and attract an owl. On at least one occasion this triggered a territorial response from a male owl resulting in the death of his female partner. It may actually be illegal to do so in Victoria.
Halls Gap is lucky enough to have a pair of Powerful Owls that regularly produce young, and are surprisingly easy to view if you know where to look. We are similarly fortunate to have a pair that have taken to regularly visiting, and roosting on, our property outside the breeding season. Lucky because (1) they are such an impressive, actually slightly intimidating, bird, (2) they are uncommon and listed as threatened in Victoria, and (3) it means the quality of habitat and diversity of prey is good enough to support them. A pair of Powerful Owls need to hunt over a large. The actual area depends on abundance of prey and ranges from as little as 300ha to in excess of 2,000ha. A pair typically requires upwards of 250 possum-sized prey animals per year.
We first found the owls on our property when I walked under a huge radiata pine en-route to checking a fox bait. An unfamiliar peevish sound came from high up and, on looking, I could make out a couple of dark shapes. Returning with binoculars I was blown away to see a pair of Powerful Owls. After that I’d check on them regularly. They would either be in the Pine or an equally large adjacent Monterey Cypress, never in any of the numerous Redgums. They roost in these exotics because the dense canopies prevent them being mobbed by other birds during the day. The Owls at Halls Gap tend to roost in large Black woods for the same reason. So, on our property the exotic pine and cypress are important owl habitat.
A good way to spot if an owl has been roosting is to search the ground underneath the tree looking for tell-tale pellets, which are grey, fur covered clumps containing the regurgitated bones of their prey. The above photo shows the collection of bones we found in the owl pellets on our property once soaked and dried out. Diet seems to vary depending on what is available but, I suspect it, also varies with individuals and, perhaps, experience. Analysis of their regurgitated pellets shows that “our” owls regularly take birds (Magpies, Currawongs, Choughs, and Cockatoos) and Kreft’s Gliders. We have never found any evidence that they take Brush-tailed Possums, despite these being abundant on our property and taken by owls in other localities, especially around Melbourne. They don’t have the opportunity to take Ring tail possums as we have none/few present. In contrast, we regularly see the Halls Gap owls with Ring tail possums, presumably as these are locally abundant. Powerful Owls can often be seen holding onto a dead prey item when roosting, presumably as an early evening snack prior to commencing the night’s hunt.
These are BIG birds with truly formidable talons and a rather daunting stare. However, they are surprisingly difficult to see. In fact, the easiest way to locate them is to look down, for white wash and regurgitated pellets. We’ve noticed that adults quite quickly get used to us going to look at them. Initially they were suspicious and watched us closely but, after a while, hardly even bothered to open their eyes when we went to check on them. The chicks, in contrast, are super inquisitive, and CUTE, moving their heads from side to side to get a good view. This head moving is so the owls can visually triangulate to assess distance and depth. Unlike us, who can move our eyes to do this, owl eyes are fixed so they must move their head. Something we’ve noticed is that quite a high proportion of individuals have damaged eyes, this may be a result of prey encounters or possibly from twigs/branches when taking arboreal prey. One of “ours” has an asymmetric pupil, handy for identification. In fact, at one stage we wondered if “our” owls and the pair in Hall Gap were one and the same. Comparison of eye-close ups (2000mm zoom !!!) showed they are different birds.
Apart from an abundant food supply, Powerful Owls need large nest hollows in big live trees, preferably with an understory of smaller trees like blackwood. The understory is an important crash pad for newly fledged owlets and provides cover for the roosting male, who will otherwise be mobbed all day by small birds, Currawongs and Magpies. When you overlay nest requirements with food sources it is not surprising that Powerful Owls are threatened in Victoria. It is great that we still have them in and around the Grampians, but we need to ensure we do, or don’t do, things to keep it that way.
Do
- Plant understory trees beneath large gums
- Revegetate, especially along creek lines, which owls like to frequent.
- Check large trees as possible roost/nest sites before using heavy/noisy machinery.
- Report roost/nest sites on public land to council, who have a legal obligation to protect them.
Don’t
- Clear large trees, live or dead
- Clear understory from beneath large gums
- Use second-generation rat/mouse poison
Nest boxes? The jury was out on these. Until recently there is only one known instance of Powerful Owls using a nest box, and this wasn’t wholly successful as one chick died. It may be that extant nest box designs/materials aren’t suitable. However, a nest box made from a natural hollow log (hoisted up a large gum) has now been used successfully for several years. So, we are considering something similar on our property with the help of skilled local arborist Nils from Calypso Hollows.
Photos and article from Clive Carlyle