- A recent study published in the New Zealand Journal of Zoology suggests that introduced invasive mammalian predators are changing the personalities of native birds.
- Researchers compared two populations of kakaruai/South Island robins in similar forest habitats, one from the predator free island of Motuara and one from the main island, where introduced predators are present.
- In the experiment, robins from the main island were more shy and less bold when they could pick up presented food items close to the researchers.
- This suggests that a selection pressure from introduced predators favours individuals that are less bold and more cautious, potentially shifting personality traits of individuals in populations under predation pressure in the long term.
New Zealand’s robins are well known for their curiosity driven behaviour, but they are at risk and the populations are declining.
The small birds only weigh 35g and can survive up to 17 years – given that they are safe from invasive predators.
While still occurring on the main islands and doing better than many other species endemic to New Zealand, that evolved in the absence of any mammalian predators, the robins struggle to survive since several predatory mammal species have been introduced to New Zealand by humans.
During their evolutionary history in New Zealand, the birds never needed to coexist with these predators and as such act in a naive way towards them, making them an easy prey for ship rats, possums, stoats, weasels and feral cats.
Introduced predators are a big problem for robins, even if populations survived until now, they are struggling where predators are present, a fate they share with almost all remaining native bird species. Predators will prey on eggs, nestlings, fledglings and adult females in the nest, leading to skewed sex ratios, where there are many more males than females in the population. The risk of nest predation is seven times higher where mammalian predators are present, and the life expectancy of adult birds is reduced by roughly 75% compared with areas free of predatory mammals.
In a recent study published in the New Zealand Journal of Zoology, researchers looked at different populations of the kakaruai/South Island robin (Petroica australis) to assess the impact of mammalian predators on their behaviour.
Individuals in two different populations, living in a similar native (kanuka Kunzea ericoides dominated) forest habitat but with a different exposure to introduced mammalian predators, were studied. One population lives on the predator free island sanctuary of Motuara and originates from a population that was never under the influence of mammalian predators, except for rats. The other population lives in two connected patches on mainland New Zealand, close to Kaikoura and is exposed to mammalian predators present at the site, including feral cats, stoats, ferrets, weasels, rats, mice and possums.
The aim was to assess the boldness of the robins or the willingness to take risks, which can vary among individuals within a species and can be influenced by environmental factors.
To assess the propensity to take risks (known as the ‘shyness-boldness’ continuum) of the birds, mealworms were presented as food items at different distances to the researchers (proximity as a risk). It was then noted how long a bird took to pick the first item up (approach time) and how long a bird took to pick up all the food items (handling time). The quicker the bird approached and the more time it spent close to humans, the bolder it was considered.
The results showed that robins not under influence of predators had a significantly bolder personality. They were much more likely to quickly come as close as 30cm to the researchers and spent more time handling the food as robins that live on the mainland, under the predation pressure of various introduced mammals.
These findings suggest an evolutionary selection pressure against bold individuals in the robin populations that are exposed to introduced predators. The predation risk has the potential to select for certain personality traits that correlate with reduced predation risk, favouring shyer birds.
The findings highlight the big impact of introduced predators, influencing the behaviour and possibly evolutionary outcomes. Individuals that are more cautious around predators are less likely to get killed and have a greater chance to have more offspring, promoting their personality traits in the next generations. These effects are likely not limited to robins, but likely also apply to other struggling native bird species that survived until now.
The researchers also point out the importance of considering behaviour in conservation actions, as shy individuals should be chosen for reintroduction or supplementation programs in areas where predators are present, to increase the chance of survival.
What you can do:
- Spread the word! Talk with other people about biodiversity issues and how to solve them.
- Value the unique native ecosystem of New Zealand and its vulnerable species.
- Promote no-go areas where birds breed and in core areas of vulnerable ecosystems.
- Lobby for better regulations and environmental standards.
- Use your vote in elections to support the effort to safe New Zealand’s unique, but highly endangered biodiversity.
- Control predators on your property. Help others controlling predators.
- Plant native plants from your region. Remove non-native plants, even if they are “pretty”.
- Participate in citizen science (e.g. iNaturalist) and help to detect various species.
- Be a responsible cat owner: cats should be microchipped, registered and unable to reproduce uncontrolled. Consider walking your cat on a leash or ensure it can’t leave your property. New Zealand’s native species are exceptionally vulnerable to predation! Feral populations are not only a huge issue for non-adapted, vulnerable species, but also an animal welfare problem for the feral cats.
- Be a responsible dog owner: dogs should be microchipped, registered and unable to reproduce uncontrolled. Walking your dog on a leash reduces the negative impact on wildlife. Dogs are among the gravest threats for adult kiwi, as they can kill a kiwi by just giving it a playful push (kiwis don’t have a sternum and are incredibly vulnerable). Ensure the dog can’t leave your presence.
This article was prepared by Master of International Nature Conservation student Maximilian Hanschmann as part of the ECOL608 Research Methods in Ecology course.
Read the full study here:
White, R., Rossignaud, L., & Briskie, J. V. (2023). The bold bird gets the worm? Behavioural differences of South Island robins (Petroica australis) in relation to differing predation risk. New Zealand Journal of Zoology, 51(2), 334–349. https://doi.org/10.1080/03014223.2023.2255165
