Although misinformation is a big problem for human society and addressing it is a big challenge, the same misinformation tactics can be used to trick invasive predators into ignoring a meal
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An adult double-banded plover (Charadrius bicinctus), also known as known as the banded dotterel or … [+]
Invasive predators, particularly feral and free-roaming house cats, can be found almost everywhere that people have ever visited or now live, and they are killing one species after another, causing many to become endangered or even extinct (i.e.; see here). At the same time, the public overwhelmingly wants to protect feral and free-roaming cats from lethal remedies, even if this means that the cat population continues to grow unchecked whilst native species are pushed into extinction. What can we do to protect native wildlife from this plague of invasive predators without resorting to lethal methods — and thereby outraging the public?
Inspired by a clever pilot study by scientists at the University of Sydney, a team of scientists in New Zealand wanted to follow up by testing whether a similar experimental scenario could be adopted as a potential non-lethal method for protecting native wild birds from being killed by feral and free-roaming cats and other discarded predatory pets.
The original 2012 study showed that mammalian predators learn to ignore unhelpful ‘background noise’ scents so they can forage efficiently (ref). The authors of that study tested whether the prior presence of ‘unprofitable scent cues’ might enhance survival of birds’ eggs and chicks compared to areas where both birds and their nesting odors were introduced concurrently. In that study, researchers confronted free-roaming predators with an onslaught of ‘fake news’ bird-nesting odors that they widely distributed throughout the landscape before introducing artificial nests. That study revealed that, in areas where predators encountered fake prey odors for weeks before any birds’ eggs were available, subsequently introduced eggs had a 62% greater survival than in areas where prey and prey odors were introduced at the same time.
Camouflaged nest and eggs of a wrybill or, in Māori, ngutuparore (Anarhynchus frontalis) in the … [+]
“It was a pilot study using artificial nests,” wildlife ecologist and lead author of the new study, Grant Norbury, explained in email. Grant Norbury is a senior scientist at Manaaki Whenua, or Landcare Research (LCR), in New Zealand where he heads up the Predator Free NZ initiative and also is the chair of a community group that is re-establishing locally extinct lizards at the Mokomoko Dryland Sanctuary in central Otago.
“We wanted to test it in a real situation at a landscape scale,” Dr Norbury added in email.
An aerial view of the Rakaia River near Christchurch on New Zealand’s South Island. The Rakaia River … [+]
To test whether introduced predator species (ferrets, Mustela putorius furo, cats, Felis catus, and European hedgehogs, Erinaceus europaeus occidentalis) can be conditioned to stop associating the scents of ground nesting shorebird species with a potential meal, Dr Norbury and his collaborators extracted odors from the carcasses and feathers of three bird species (chicken, Gallus gallus domesticus; Japanese quail, Coturnix japonica; and kelp gull, Larus dominicanus). By mixing odors from three different birds, the scientists encouraged the invasive predators to generalize between the prepared odors and the odors of different species of live nesting shorebirds, rather than distinguishing between (and potentially targeting) specific species.
Extracted odor samples were added to Vaseline petroleum jelly, heated and mixed thoroughly, then transferred to plastic syringes and stored at −20°C until needed. These odors were applied to rocks and gravel in New Zealand’s natural braided river ecosystems for 5 weeks before shorebird arrival and for 8 weeks thereafter during the breeding season of native ground-nesting birds (double-banded plover, Charadrius bicinctus; wrybill, Anarhynchus frontalis; and South Island pied oystercatcher, Haematopus finschi). These extensive ‘fake news’ scent treatments were applied every three days for two breeding seasons (Figure 1).
F I G U R E 1 : The study area showing the study species (predators and native ground-nesting … [+]
As predicted, Dr Norbury and his collaborators found strong evidence for habituation to unrewarded nesting bird odors by ferrets (Figure 2A) and cats (Figure 2B) before and during shorebird nesting. This finding is expected because animals don’t want to waste their time and energy looking for something that isn’t there, so after the shorebirds did arrive and begin nesting, the pre-conditioned predators lacked the motivation to pursue them, thereby leaving their initial scent misinformation uncorrected.
As you can see in these graphs, interaction times with unrewarded nesting bird odors were initially high but declined after 12 to 18 days. By the time shorebird nesting began, predator interactions with odor were only at 5 to 9% of their initial levels.
F I G U R E 2 : Habituation of predators to unrewarded bird odor. Total interaction times (and 95% … [+]
Hedgehogs, on the other hand, showed a different pattern of interactions with unrewarded nesting bird odors. As you can see in the graph, hedgehog interactions rose steadily, peaked 18 days into the nesting season and declined thereafter (Figure 2C).
This difference stems from their different life histories: unlike cats and ferrets, hedgehogs hibernate. Camera traps helped to nail this down. They first photographed hedgehogs between 11 and 28 days after the fake odor deployment campaign began, suggesting that they were gradually emerging, quite hungry, from hibernation. Unfortunately, this phase of increased hedgehog interactions with fake scents of nesting birds coincided with the arrival of shorebirds and the onset of nesting, which slowed their habituation.
F I G U R E 3 : Hatching success (HS) of birds with and without odor treatment. Predicted HS of … [+]
Dr Norbury and his collaborators then modeled how their massive misinformation campaign of nesting bird scents might affect shorebird survival in the future. Their models predicted that odor-treated sites resulted in a 127% increase in modeled shorebird population size in 25 years (Figure 5). This predicted population increase is huge for declining bird populations.
F I G U R E 5 : Average VORTEX population projections (and 95% CIs) from a starting population of … [+]
Dr Norbury and his collaborators also mentioned that tricking cats and ferrets into ignoring ground-nesting shorebirds using treatments of unrewarded bird odors was easy and inexpensive, with costs of about NZ $33 per hectare (including odor extraction) for 30 days of treatment. The total treatment time used for this study was 66 days.
Are there limitations to this method of trickery?
“It depends on a number of things like whether the predators have access to an alternative high value food,” Dr Norbury replied in email. “If they don’t, the method is unlikely to work.”
There is much to recommend this innovative conservation method. Altering cats’ and ferrets’ perceptions of prey availability before shorebirds arrived and began nesting tricked these invasive predators into ignoring an otherwise meaningful food cue. This innovative, nonlethal and low-tech method for managing problem predators reduced shorebird nest predation and improved conservation outcomes for threatened species. Further, it shows promise for also managing individual endangered predators that have become a problem by selectively preying on other vulnerable or endangered species.
“[A]ltering predator behaviour, rather than killing them, can sometimes lead to positive conservation outcomes,” Dr Norbury agreed.
Grant L. Norbury, Catherine J. Price, M. Cecilia Latham, Samantha J. Brown, A. David M. Latham, Gretchen E. Brownstein, Hayley C. Ricardo, Nikki J. McArthur, and Peter B. Banks (2021). Misinformation tactics protect rare birds from problem predators, Science Advances 7:eabe4164 | doi:10.1126/sciadv.abe4164
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