By Nic Rawlence 16/12/2021

The hunter stalks its prey through the forest, following the wafting invisible trail of musky odor straight to the kiwi burrow. Within a few months, the dog has killed over 20 kiwi.

You would think this event occurred recently, given the frequent headlines of dogs killing or attacking our unique wildlife, or the feral dog populations causing trouble in northern Aotearoa New Zealand. Rightly these headlines produce collective anger from kiwis (the people, not the bird, though I imagine the birds would no doubt be pretty pissed off at the current situation).

But travel back in time to when humans arrived in New Zealand over 700 years ago in the late 13th Century and there is a distinct blind spot when it comes to human’s best friend back then, the kurī (Polynesian dog). The prevailing view is that kurī had minimal ecological impact, despite scientists accepting the myriad of other impacts Polynesian, and later European, colonization had on New Zealand from extinctions to the widespread burning of forests, and the introduction of mammalian predators.

Cultural taonga: As well as human’s best friend, kurī were an important cultural resource for Māori.

The difficulty of assessing the impact of kurī has meant they are frequently disregarded in the annals of the ecological consequences of human arrival. Some scientists have even boldly gone where no one has gone before in stating “the Polynesian dog can be exonerated: it was kept so close to camps that it is not a factor”, so much so that this has become established scientific dogma (sorry) for the past 20 years despite no evidence to support this. I’m reminded of something I learned in my undergraduate days; that the absence of evidence is not evidence of absence. Why wouldn’t kurī have had a significant impact on New Zealand’s biodiversity, including contributing to the suite of extinctions that occurred shortly after human arrival? Personally, it’s a no-brainer. With this in mind, Karen Greig and I combined our archaeological and palaeoecological expertise in our newly published paper to find out the potential impacts of kurī on New Zealand’s pre-European ecosystem.

When Polynesians arrived in New Zealand, they brought with them two culturally important commensal animals, who just happened to be furry predators, sharp in tooth and claw: the kiore (Pacific rat), and kurī. Kiore rapidly spread throughout the country and had a big impact along the way. Their arrival can be seen in the natural fossil record from the sudden appearance of rat-gnawed seeds in sediment cores to the extinct laughing owl hunting kiore as an evening meal. There were doubtless numerous extinctions of small animals and invertebrates caused by these novel predators that we are yet to discover.

Kurī were kept as companions, watch dogs, and hunting dogs. They were also an important cultural resource for meat, kahu kurī (dog skin cloaks), and bones for tools and ornaments. So far, kurī bones and coprolites (desiccated dog poo) have only been found in archaeological sites (though we’ll get to the question of feral kurī soon) but that doesn’t mean their impact would have been any less significant. Substantial numbers of dog bones have been found in pre-European archaeological sites suggesting sizable kurī populations.

New Zealand was rapidly colonized by humans, to the point that in the archaeological record, they appeared everywhere at once. And where ever humans were, their best friend was as well. Look at the distribution of pre-European archaeological sites in New Zealand, and the impact of kurī becomes clear.

Using what we know of the impact of dogs in New Zealand and overseas, we can hypothesise what sorts of impacts kurī had on New Zealand’s naïve ecosystem. It’s highly likely kurī filled a predatory role in the new post-human ecosystem by targeting medium-sized prey. Birds were the obvious targets including waterfowl (goose, ducks, mergansers, poūwa swan), small moa, adzebill, takahē/moho, other rails, kākāpō, kiwi, and ground-nesting seabirds including penguins, shags, and burrowing seabirds. But also seals and rāpoka sea lions (especially pups), and reptiles such as tuatara, skinks, and geckos.

The dog is in the henhouse: Many of Aotearoa’s animals had no defense against furry predators and potentially fell prey to kurī. Figure from Greig and Rawlence (2021).

New Zealand’s fauna evolved for millions of years in the absence of mammalian predators. Rather the top predators in the pre-human ecosystem were birds like the mighty Haast’s eagle and Eyles’ harrier, which hunt by sight, all the better to see you with. There’s a reason why many of our birds are drab, camouflaged, and freeze when predators are around. Sadly, it doesn’t work when our birds stink to high heaven (sorry, kākāpō) and can be smelled from a mile off by introduced mammalian predators. Granny, what a big nose you have! All the better to smell you with. Add to that, many of our unique animals are terrestrial, flight reduced or flightless, ground-nesting, prone to disturbance, and slow at breeding. All fine in an ecosystem that’s in balance but not when a new predator arrives in town.

Keeper of secrets? Kurī bones may hold the key to how big the impact of dogs was in pre-European Aotearoa. Photo by Guy Frederick.

To limit the impact of kurī to direct hunting (whether for their own needs or going on a moa hunt…) is too simplistic. The reality is much more nuanced and no doubt also included direct competition for prey or carrion, disturbance to animals (including chasing, colony disturbance, and abandonment), changes in prey behaviour that could lead to decreased reproductive success, and the transmission of diseases. These novel microscopic threats could potentially decimate populations of naïve animals – much like how diseases introduced by Europeans decimated indigenous populations around the world. Dog parasites, which can also be spread by rats, have been found in kurī coprolites. It’s likely that the myriad of impacts of kurī evolved over time as both they, and their human counterparts, adapted to a temperate (and rapidly changing) post-human New Zealand compared to their tropical homeland.

Historical records indicate that by the early stages of European colonization in the 19th Century, feral dog populations were a big problem, especially for sheep farmers. It is not known whether kurī were part of these feral packs or if they were already extinct due to interbreeding with European dogs and genetic swamping. Yet there is every chance kurī formed feral populations before European arrival, just as there are feral dog populations in northern New Zealand today. While the jury is still out on this, we need to scientifically entertain this possibility. Feral populations likely had a proportionally greater impact in areas where human population density was low. There are numerous dog bones from pre-European sites with no strong archaeological context that could potentially represent feral kurī. Equally, apex predators could be at such low population densities that they are effectively invisible in the fossil record.

Overlooked no longer, far from being exonerated, kurī should be included in models of human impact, whether they were independent of humans or not. Kurī mirrored and amplified the already significant impact of Polynesian colonists and their Māori descendants before the arrival of Europeans, and their own horde of furry beasties. Many questions remain unanswered and only further research will tell just how big the impact of kurī really was.

An extinction vortex: Kurī should now be included as having contributed to the ecological consequences of human arrival. Figure from Greig and Rawlence (2021).