The Australia Brushtail Possum

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Introduction: The Australia Brushtail Possum (Trichosurus vulpecula Kerr) is an introduced pest to New Zealand. Devices are set up to detect the presence of possums in certain areas. This information is used to determine where possum control is necessary and how effective it has been. Other than trapping, the most common detection devices are wax tags, and chew-track cards. The latter of the two being a rectangular piece of core flute/corrugated plastic, into which a bait (usually peanut butter) is forced down the flutes and then nailed onto a tree. The purpose of this is to attract possums with the white coloured plastic, and the smell of the bait encourages them to chew on the card. They then leave their tooth indentations on the chew card. The only problem is that it attracts more than just possums. Chew cards can be chewed on by hedgehogs, feral cats, stoats, ferrets, mice and especially rats. The Problem: Rodents are a nuisance when it comes to detecting possums because they can completely gnaw through the plastic of the chew cards and obscure any sign of possums. Possums bite on the chew card and try to pull the bait out, but don’t usually chew right through the plastic - they tend to crush it. My project explored different methods to exclude rodents; physical deterrents and odour/flavour deterrents. In some areas where there is a large abundance of rodents, even if a rat bites the chew card once and then decides it doesn’t like the flavour, there may still be enough rats in the area for many of them to do the same thing and obscure detection of the target species. For this reason, I decided to test whether the odour of the bait could repel rats and discourage them from biting the device. I also tested possible devices which would physically exclude rodents. The Devices Chew cards, as described above, were used as a way of presenting my smelly baits to wildlife. Spoked chew cards are chew cards with a bicycle spoke through the middle flute and one end is bent to prevent the chew card from being pulled off (see model). The chew card is free spinning and a blob of hot glue was used to stop it from sliding too far up the spoke. Because the card can spin the rat cannot balance on it, and falls off. The concept of the spoked chew card was not my own idea, it was originally developed by Landcare Research*.
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