In a world where many predators hunt with their noses, odor trickery can be a key to survival. Puff adders in Africa seem able to avoid detection by sharp-nosed meerkats and dogs. Shorebirds change the composition of their body oils while nesting in ways that make them hard to sniff out. Fish that dine on coral might match the smell of the surrounding reef, camouflaging them from hungry cod.
Now, ecologists in New Zealand and Australia think wildlife managers should consider a similar tactic to help protect endangered species. And they have evidence suggesting that, at least in one setting, it works.
“We are starting to tease apart the ecological basis of olfaction and to understand how animals use smell and why they behave the way they do – and how we can use that knowledge to save species and protect ecosystems,” said University of Sydney ecologist Catherine Price.
Price lives in a part of the world where invasive mammals including rats, stoats and cats are running amok, devastating native wildlife that evolved before such predators arrived with European colonizers. New Zealand and Australian wildlife managers have struggled to fend off the assaults, resorting to widespread use of poisons, traps, hunting and fences, with mixed results.
But such tactics – which are used around the world – can come with downsides. Animals that aren’t targeted might fall victim to such measures. The bloodshed can prompt objections. And sometimes these approaches aren’t sufficient.
So how about messing with the sense of smell used by animals ranging from sharp-toothed predators to herbivores?
Odors can give animals a leg up in their hunt for food, helping them detect it before it can be seen and enabling them to zero in on its location. Price and company suggest a variety of ways this might be foiled in the name of conservation. Wildlife managers could spread smells throughout an area that imitate the scent of an organism they want to protect, forcing predators to chase decoys and having less chance of finding the real thing. New smells could camouflage the presence of certain organisms – like an air freshener that covers up those stinky socks. Predators could also be trained to think a particular smell isn’t really connected to food, the scientists write in a new paper in Frontiers in Ecology and the Environment.
“We’re just hiding things in plain sight,” said Price. “Foragers are using smell to find things, and when they can’t find it in all the background smells, they’ll start looking for something else.”
The concept isn’t entirely new. Gardeners, for example, plant marigolds near their crops to ward off pests. Scientists have documented the effectiveness and traced it to odors emitted by the flowers.
But it is currently not a widespread tool in conservation circles. Price and colleagues point to an experiment they conducted to illustrate how it might work.
On New Zealand’s South Island, the scientists set out to see how well odors might protect native ground-nesting birds – double-banded plovers, wrybills and South Island pied oystercatchers – from marauding ferrets, cats and European hedgehogs.
As the birds arrived for nesting seasons in 2016 and 2017, the researchers smeared a brew of Vaseline and fat from quail, chickens and kelp gulls on rocks in habitat totaling around 20 square kilometers.
Then they set up cameras to track the behavior of predators near places marked with the odors. They also monitored the birds to see how well they fared in areas marked with scents, compared to comparable spots with no extra bird smells.
The cameras showed that while the predators at first spent a lot of time sniffing around the scented rocks, they quickly learned these odors didn’t correspond to a meal and spent far less time there.
While the trick-smells were from different species, this loss of interest appeared to carry over to the real nests. Eggs hatched and survived as chicks nearly twice as often in places treated with the paste. That could translate into a 127% increase in bird numbers over 25 years, the scientists reported last year in Science Advances.
That doesn’t mean such approaches are a silver bullet. Wildlife managers would need to figure out which smells to imitate or mask, and how to do that, the researchers noted. It could require studying the chemical signature of odors to find ones that work in a particular situation. People would also need to figure out which strategy is likely to work, how big an area they need to cover, and how long they would need to do it, among other things.
“There is still a lot to understand,” said Price. “But this is a new, powerful tool to add to the kit of wildlife managers.”
Price et. al. “Olfactory misinformation: creating ‘fake news’ to reduce problem foraging by wildlife.” Frontiers in Ecology and the Environment. June 21, 2022.