Alpine kea (Nestor notabilis) trap tampering

New Zealand is famous for many things—its rugby team, its natural beauty, a series of epic fantasy films—but it should really be best known as a realm of birds. Alongside such species as the moa, kakapo, and kiwi, most of this island nation’s non-aquatic birds are (or were) found nowhere else in the world.

When human settlement of Aotearoa began some 700 years ago, over a third of the large land birds were flightless, and they were naive to the dangers of getting too close to people. Those classified as food or pests, or overlapping in their ecology with newly introduced mammals such as rats and livestock, quickly began dying out.

Today we’re looking at one of those unique birds, the kea. There are only a few thousand of the world’s only mountain parrot left alive today, found generally in the west and central regions of New Zealand’s Southern Alps. And despite all the risks of meddling in human affairs, it seems they just can’t help getting into trouble.

Poking around

Unlike kiwis or kakapo, kea are able to fly, with a strong curved beak and a diet of plant parts and invertebrates. They can be destructive feeders, breaking into dead wood and digging in the soil. They are also one of several birds known to use tools when held in captivity, but not in the wild. In the 2018 publication that forms the basis for this post, Matthew Goodman and his colleagues pulled together data on species that share this ‘captivity bias’. Most are members of two groups, the corvids (crows and their relatives) and the psittacines (parrots and cockatoos), despite these groups only making up around 5% of bird species. The authors suggest that the frequent use of corvids and parrots in laboratory experiments, as well as an abundance of pet parrots, may have contributed to their known technological record.

Human activity also plays its part in the first account of kea tool-use in the wild, although we need a quick detour via one of its avian cousins to reach that point. For the first half of the twentieth century, the ground-nesting takahē (Porphyrio hochstetteri) was presumed extinct on New Zealand’s South Island. This large bird stood some 50cm tall, red-billed and red-legged with blue and green feathers, and was apparently quite tasty. Here’s a takahē, with its chick:

The takahē remained a museum specimen from 1898 until 1948, when live birds were re-discovered in the Murchison Mountains near Lake Te Anau. A report from 8 January 1949 in the Otago Daily Times captures the sense of excitement and potential:

If the Lake Te Anau country could conceal for 50 years a bird as big as a takahe, enthusiasts feel that it may have moas, too, perhaps even giant moas 12 feet tall.

Unfortunately moas remain elusive around the lake, just as they are everywhere else. What did show up, though, were invasive stoats (Mustela erminea).

Stoats are wily mammalian predators, difficult to catch and kill, and flightless birds are a poor match for them. Beginning in 2002, the NZ Department of Conservation (DoC) set stoat traps in the Murchison Mountains in an attempt to drive down their numbers, and give the few hundred remaining takahē a fighting chance. The traps usually consisted of a box with spring-loaded meat or egg baits, with more than 700 of them spread across the region. And that’s where the kea re-enter our story.

From the earliest use of stoat traps, the field workers responsible for checking them found that the traps were often tipped over. They suspected that the physically exploratory kea were involved, but had no proof. As Goodman et al. describe, tying down the boxes didn’t necessarily help:

After trap-boxes were secured to the ground with steel or wooden pegs, trap-boxes were still tipped over. Kea did this by first digging around the securing pegs until they were loose enough in the ground to allow the trap-box to be tipped over. The birds also removed the lids of trap-boxes by initially removing screws securing the lids that had become loose over time… After loose screws were secured kea then excavated wood around screws to remove lids.

Not tool-use yet, but clear signs of both curiosity and a low threshold for vandalism. It wasn’t until around 2009 that the kea stepped up their arms race against the DoC. From July 2009 to June 2010 around 70% of trap boxes in some areas were sprung by inserted sticks, and kea were the prime suspect.

The earlier traps had a few wire strands across the ends, to stop larger animals (like takahē) from getting inside. But those traps didn’t stop kea from inserting sticks to set off the trap. And when finer mesh was used to prevent ready stick-tool-use, the kea removed strands of the mesh itself and used those to probe into the trap. Finally, the DoC staff resorted to a combination of steel plates at the trap ends and a side entrance to the trap—meaning that inflexible sticks couldn’t be used to reach the trap, but stoats could still get in—as well as steel brackets protecting the screws. Those armoured puzzle boxes did the trick, and the kea were thwarted.

Here’s an image from Goodman and his co-authors, showing sticks inserted into the initial trap version (A), a version with tighter mesh (B), a trap completely overloaded with inserted sticks (C), and the ‘side-entrance’ final trap version, with inserted sticks that failed to reach the trap mechanism (D):

Overall, from late 2010 to late 2014 (with some missing data), keas used 250 sticks to try to access food in 227 trap boxes. They particularly targeted egg-baits, perhaps because breaking the egg inside a trap still allowed the kea to eat the contents that ran out the ends. Collectively, this sustained disruption of the stoat trapping program is the first rigorous evidence of non-human animal tool use in New Zealand.

And in case you’re wondering if there’s video evidence of this tool-use, yes there is. Motion-activated cameras caught them in action:

Thoughtful response

Wild kea had never been seen using stick tools, which strongly indicates that this was an innovation by the Murchison Mountains birds. On one hand, the question of why the birds were trying to spring stoat traps seems obvious: they wanted the clearly-visible food. But Goodman and his team weren’t completely satisfied with that idea. For one, the traps were present for years before the first tactical twig insertion. Even though the boxes were physically manipulated during that time, it wasn’t as though kea had just been waiting for their moment to pick up sticks and get to work.

Instead of this being a case of releasing pent-up abilities, the researchers propose that the kea probing activities were bumping against an upper level for how they respond to cognitively demanding tasks. As natural extractive/destructive foragers, the idea of getting into things is a natural part of the way kea approach the world. The initial trap design allowed the birds to see the bait through the ends, and to insert a tool from that same position directly towards the food. Plus there were literally hundreds of these traps, continually baited and re-baited, giving plenty of exposure to those kea who were interested in them.

Despite all those advantages, the fact that it took years for kea to begin using probe tools on the traps suggests to the scientists that it is a difficult task. And there are other areas in the South of Aotearoa with both traps and kea where the same behaviour either didn’t occur at all, or did so at very low frequency. Because most of the tool-use wasn’t observed by humans, there is no clear data on how many individual kea were involved in this behaviour (the problem is essentially an archaeological one, where actions have to be reconstructed from scant and varying evidence after the fact). However, the research team couldn’t rule out only a small number of birds doing most of the probing: flying kea can cover tens of kilometres, or much of the area in which stick tools were found.

The authors note that there are other opportunities for tool use in the alpine environment. If the kea are able to translate what they’ve learned about tool use across to natural probing sites—in trees, for example—then that behaviour should begin showing up in surveys of kea activity. If, instead, the traps represent a particular environmental confluence of the right set-up and level of cognitive demand, then the trap modifications and armour plating may put an end this bout of wild kea tool use.

That’s not to say that future (or past) tool-use is out of the question for wild kea. They are playful animals, with the curiosity to explore unusual outcomes of that play. Goodman and his colleagues even suggest that the bait might not have been the target of kea probing in all cases:

kea might have probed into run-through trap-boxes that they probably knew were unbaited because the effect of setting off snap-traps was intrinsically rewarding.

In other words, just getting that snap may have been an interesting outcome to the birds, an effect that’s probably familiar to anyone who’s spent a few satisfied minutes popping bubble wrap.

Captive kea are getting increasing attention for their ability to reason through physical and even statistical problems in the laboratory. We will certainly be hearing more about them in the coming years. What the snap-trap tool-use tells us, at a minimum, is that the way these birds think is intrinsically linked to how they behave, and the way their actions modify their environment. To understand that process more clearly, laboratory studies aren’t going to be able to recreate the full variety of the kea’s mountain home. Sometimes the best way to understand an animal is to meet it on its home turf, and maybe keep an eye out for moas while you’re there.

Sources: Goodman, R. et al. (2018) Habitual tool use innovated by free-living New Zealand kea. Scientific Reports 8: 13935. || Bastos, A. & A. Taylor (2020) Kea show three signatures of domain-general statistical inference. Nature Communications 11: 828.

Takahē image credit: Rod Morris, New Zealand Geographic (1999) Jan-Mar issue 041 || Trap image credit: Goodman et al. (2018) || Video credit: ScienceVio, YouTube