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"Rat sausages" prove tempting to stoats

Mon, 27 Sep 2004

"Rat sausages" prove tempting to stoats

Researchers have cooked up some winning recipes with aromas to entice a ferocious predator * the stoat. The smelly substances include unique PVC "rat sausages", and show promise as long-life lures to attract stoats. Stoats were brought to New Zealand in the 1880s to control rabbits, but have wreaked havoc on many native bird species.

Cost-effective ongoing control of stoats is crucial for maintaining viable populations of native birds including kiwi. However, stoats are elusive and therefore difficult to poison or trap. Improving the attractiveness and longevity of lures for traps and bait stations is one key to boosting the success of stoat control. In a project commissioned by the Department of Conservation, Landcare Research staff set out to devise new, long-lasting and attractive lures for stoats.

Hen's eggs are currently the main lure used, and last for several weeks. However, preliminary research by Landcare Research showed that stoats are more attracted by the smell of dead prey such as birds and rats.

The obvious problem with this is that dead prey decay rapidly. Researchers therefore aimed to encapsulate the smell of rats within a stable substance * and to keep the smell "smelly" long-term. Landcare Research ecologist Dr Andrea Byrom says four substances were trialled for use in new baits: cereal, gel, casein, and PVC. "We incorporated ground up, freeze-dried rats into the substances, and placed them in trap-like tunnels in the open air. We checked them for intactness and odour weekly for 20 weeks.

"The PVC lures remained fully intact, while the others broke down. The PVC lures were formed in test tubes and looked like meat sausages * albeit with rat hair in them!" Researchers then tried the PVC "sausages" with a new flavour: "chemical rat". "We identified key components in the odour of live ship rats, and mimicked them with similar-smelling synthetic chemicals.

We then incorporated these chemicals into PVC lures," Dr Byrom says. "We set up a new trial comparing the attractiveness of the lures to stoats. We placed tunnels in the pens of 18 captive stoats, and monitored the stoats' interest in tunnels containing either the freeze-dried rat PVC lure, the 'chemical rat' PVC lure, fresh dead rat, and no lure at all. "The results of this trial were also encouraging. We found that more stoats entered tunnels containing the freeze-dried rat lure than tunnels with no lure. Also, the first tunnel that stoats entered was equally likely to have the freeze-dried rat lure, the chemical rat lure, or fresh dead rat. In other words, the chemical rat lure was at least as attractive as fresh dead rat.

"These results show that the freeze-dried rat lure and chemical rat lure both have potential for attracting wild stoats to traps and bait stations in the field. "However, further work is required to get exactly the right combination of attractiveness and longevity in the baits." Dr Byrom says the attractiveness of these lures now needs to be tested in field trials in wild stoat habitat.

"We would also like to investigate the potential of incorporating other prey odours such as rabbit into PVC lures to attract other predators such as ferrets, weasels and cats. "Our PVC lures were made purely for smell. However, research shows that lures that look or move like prey may also be very attractive. We may investigate this in future." Department of Conservation Stoat Control Research programme manager Dr Elaine Murphy is pleased with the promising developments.

"Having a new tool for the toolbox would be great, and the new lures would be a lot less trouble to carry around in the bush than hen eggs," Dr Murphy says.


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