Robins are among our most charming forest birds, known for fearlessly approaching trampers and even hopping onto shoes, backpacks, and hats. But research suggests introduced predators may be turning them into more cautious, fearful birds.
Kakaruwai (South Island robin), the rotund grey birds with legs the size of toothpicks, are a delight to encounter in the forests of Aotearoa. They make you feel special when they follow you along the track in the pursuit of insects, some even hopping onto your shoes, bag, or hat. But their friendly personality is under threat.
Research in the New Zealand Journal of Zoology suggests introduced predators aren’t just reducing kakaruwai numbers: they may be changing their personalities, too.
The boldness test
The researchers looked at two kakaruwai populations to test their theory.
One population live on predator free Motuara Island in the Marlborough Sounds; the other survives in bush full of introduced mammal predators on mainland New Zealand, near Kaikōura.
Researchers investigated the differences between shyness and boldness, defined as an individual’s reaction to a risky but not novel situation.
To test their avian audacity, the researchers timed an individual bird’s willingness to approach to collect a mealworm larvae snack. On predator free Motuara Island, the robins strutted right up to the treat. The Kaikōura birds were noticeably more hesitant.
The survival advantage
The constant exposure to an environment full of predators is seemingly prompting friendly robins to dial back their boldness in favour of caution. This is good for their survival, the researchers say.
“Shyer responses may be more advantageous as they may make them better at avoiding mortality through predation from a wide range of introduced mammalian predators that are present.”
Meanwhile, the continued bold behaviour is also advantageous on Motuara Island, as robin densities are around ten times greater and bolder responses allow individuals to be more successful competitors in gaining territories, mates and food.
Are we witnessing the evolution of a more cautious generation of mainland robins? The study doesn’t definitively say whether these differing robin personalities are coded in their genes or influenced by learning.
“However, if environmental conditions show directional change, selection can favour one personality tendency, causing it to become more prevalent over time,” the study states.
The implications of these behavioural differences could play an important role in programmes for translocating and managing bird populations. Birds from island populations are sometimes used to reintroduce or supplement populations on the mainland.
If too many bold individuals are moved to create a new population, they may not thrive due to a lack of caution around predators.
Controlling predators and achieving the Predator Free 2050 goal would help bring nature back into balance so robins can live their best, bold lives again on mainland Aotearoa New Zealand.
You can access the full study online, written by Robyn White, Laureline Rossingnaud and James Briskie and published in the New Zealand Journal of Zoology.
