A pied-piper for possums?

“Hello? Anyone there?”

One of the issues with running a blog, such as EcoLincNZ, is in attracting an audience. It’s a big online world out there with plenty to read. Finding and attracting readers is a major headache. We use several strategies. There is a link from our departmental site, a link on the Lincoln University outreach site, the address is in the signatures on our emails, we announce new articles on our Department of Ecology facebook page and with LU tweets to alumni. We have made the recent content of the site a round of questions in our annual Year 12 Big Biology Quiz for Canterbury school students. We advertised at the New Zealand Ecological Society conference held at Lincoln last year. Often people find us through Google searches and the like. Last year we had a blog on ‘Bigfoot in NZ’ which was about carbon footprints and presumably disappointed the 1500 Americans that looked at the article over the first couple of days. Last week we had a surge in hits on our article ‘Watch me Wallabies Feed, Mate’ when Rolf Harris was in the news. Of course, we really want people finding the site to interact with it; read the whole article, maybe leave a comment, click around and read some more articles. Finding ways of getting our targets (that would be you dear reader) to find and interact with the blog articles takes up a bit of our time. Interestingly, a very similar issue exists in wildlife management where getting a pest, say a possum or a rat, to find and interact with our devices, such as a camera-trap, bait station or tracking tunnel, also takes up a lot of our time.

If you have a large population of pests, say possums, and you place a device in the field, chances are that some individual possums will bump into the device simply because there are so many possums about. After a control operation when the possum population has been reduced dramatically, there is much less chance of the remaining individuals finding your device. There are several tricks by which you can increase the chances of an encounter. There could be a colour or a scent added, for example. One of the difficulties with these methods, especially in forest, is that these lures only work over short distances. One potential method to provide a larger zone from which to draw a possum to your device is to use sound.

Matt Kavermann has just completed a PhD where he looked at the potential of sound to act as a lure to stimulate possums to come to a site and to interact with a device, like a bait station or waxtag. Possums are curious animals and when they find something unusual in their territories they will generally investigate it (which usually means biting it thoroughly). Matt, with his supervisors James Ross and Adrian Paterson, developed several generations of devices that produced audio lures (usually a high-pitched beep). The idea was that a possum would hear the noise from a distance and be guided to the waxtag or chewcard which they would bite and leave evidence of their presence. To test this idea, Matt set up an experiment in beech forest at Mount Misery at the south-eastern end of Lake Rotoiti in the Nelson Lakes National Park. Matt had 48 monitoring sites located in a 150m x 150m grid. Half of the sites had the audio lure (a beep every 15 minutes)and half were silent. At each site Matt had a waxtag or a chewcard to record possum presence. Matt checked these sites daily for 10 days. Given the terrain, it’s not called Mt Misery for no reason, this was a huge effort.

Matt’s results have just been published in New Zealand Natural Sciences. Matt found that the audio lure increased possum detection at chewcards by 30% and at waxtags (which are not as sensitive) by a whopping 900%! There was evidence that the audio lure was dragging in possums from over 300m away to the detection site. It appears that possums do hear the lure and are curious about what is causing it. They move to the source of the sound and are more likely to interact with the device placed there. This is excellent news for possum control. Audio lures may be a great way of counting how many possums survive an intense control operation. Better yet, audio lures may provide a way to target these remaining individuals to reduce pest populations to zero by encouraging them to move to a site with toxic bait. The pied piper was able to remove all of the rats from Hamlein by playing his music. Maybe he was onto something!

“I’m sure that sound came from over here”

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