New study finds predators can be tricked into ignoring native bird scents

Wednesday, 10 March 2021

Dr Grant Norbury sets up camera traps to catch predators in Tekapo.

A new research project has successfully taught roving cats that the scent of a tasty banded dotterel might just be a red herring.

The Manaaki Whenua – Landcare Research and University of Sydney study, published in Science on Wednesday, saw researchers set “fake clues” for mammalian predators along braided rivers in Canterbury’s Mackenzie Basin.

The lead researcher, Landcare Research’s Grant Norbury, said introduced mammals like cats, ferrets, and hedgehogs use smell as their main cue when hunting.

Over two breeding seasons, scientists created an “odorous paste” from bird carcasses and feathers, and spread it at more than 300 camera-monitored nesting sites before the birds arrived to lay their eggs.

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A hedgehog falls victim to the fake bird scent.

“Our target species were banded dotterels, which are on the decline, as well as wrybills, and South Island pied oystercatchers, which are all incredibly vulnerable because they nest on the ground.”

Norbury said they monitored predators’ behaviour at sites with the paste versus sites without it, and found all three types of predator were attracted by the paste odours, but ferrets and cats in particular quickly lost interest when there was no prey associated with the scent cues.

“When the birds arrived to nest, the predators had already altered their behaviour by ignoring bird odour, including that of the real birds.”

He said the effects on nest survival were striking.

Compared to untreated sites, nests where predators had been desensitised to bird scents had a 1.7-fold increase in the number of chicks produced.

Researchers estimate for banded dotterel, if this type of intervention was used every year it could see the population size more than double over the next 25 years.

“It’s a non-lethal method,” Norbury said, “so it has advantages in places where lethal methods can’t be used.”

Examples include urban areas where the predators might be people’s pet cats, or overseas where the problem predators are also native species.

“We don’t have to actually remove any predators. All you’re doing is messing with their minds.

“It obviously doesn't solve the problem entirely, but it’s another tool in the tool box.”

The banded dotterel – or pohowera – is considered nationally vulnerable, although its threat status is due to be reviewed by the Department of Conservation this year.

The number of birds was estimated to be around 40,000 nationwide at the time of the last review in 2016, but researchers now believe that number has dropped to as little as 16,000.