Where There's Prey
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For many years now, possums have been on the increase in Sydney suburbs but until recently, not followed by their predators.
Walk around any well-treed suburb at night and you’ll often see good numbers of both the Common Ringtail and Common Brushtail possum – even though nearby bushland populations are much sparser.
Why so many? Well, abundant food, lots of nesting sites in roofs and sheds, and a lack of predators all play a part. There’s even a suggestion that ringtail possums are spreading thanks to the network of optic-fibre cables, which has made crossing the road so much safer for these highwire acrobats.
Sure, some domestic cats will kill a ringtail, but many responsible people (commendably) are keeping their pets inside at night or using cat cages to prevent such problems.
While adult brushtail possums make formidable opponents for all but a large, fast or very brave dog, a number are still killed on the roads – though seemingly not enough to affect their urban population.
So where are the possum predators? Large pythons, goannas and even quolls are occasionally lured into bushy suburbs by this abundance of prey – only to be captured by wildlife welfare people and returned to their bushland homes. Needless to say, these species have not yet established large urban populations.
An exception is that formidable possum predator, the Powerful Owl, Ninox strenua. Once rare enough to be classed as endangered, this large owl is now almost out of the woods – literally and figuratively. Following possums into the suburbs, it is now seen so regularly it barely rates a mention.
What surprises me is the extent to which it has penetrated the city. I’ve seen a breeding pair in the Royal Botanic Gardens in Sydney, others perched next to the Pacific Highway in North Sydney and even some wise owls on campus at Sydney University.
Then there was the temporary resident of a large tree outside a Museum window a while ago. For quite a few days, we could observe this owl’s catch from the night before – mostly rats, pigeons, currawongs or flying-foxes. But one day its talons held a fully grown brushtail possum. By lunchtime there was half a possum and by the following morning, none. That’s an impressive appetite! I’m told that during the possum breeding season the Powerful Owl will simply pluck a baby brushtail from its mother’s back – presumably as a snack.
What this owl and possum trend tells us is that wherever there is an abundance of any kind of animal or plant, sooner or later something will probably show up to feed on it. So why not check out the possums in your area and look out for their predators too.
Martyn Robinson is the Museum’s resident naturalist.
First published in Explore 33(1).