The History of Rodents in Aotearoa: How Rats and Mice Became a Conservation Crisis

You’re walking through native bush. The canopy shimmers with birdsong, and the undergrowth rustles softly. But beneath the ferns and fallen logs, a quiet threat lurks-one that arrived by boat, stayed by accident, and changed Aotearoa forever.

Rodents-rats and mice-aren’t native to New Zealand. In fact, they are some of the most destructive stowaways in our ecological history. Understanding how they arrived, spread, and wreaked havoc on our landscapes is vital to reversing the damage they’ve caused. Here’s how it all began.

First Wave: Kiore - The Polynesian Rat

The story begins with the arrival of the first humans. Around the 13th century, Polynesian voyagers landed in Aotearoa, bringing with them a suite of plants and animals-including the kiore, or Pacific rat (Rattus exulans).

While not introduced intentionally, kiore quickly became part of both the ecosystem and Māori life. Archaeological and DNA evidence suggests they spread rapidly across the mainland and offshore islands. Culturally, kiore held significance for some iwi, who valued them as a food source and part of traditional knowledge systems.

Ecologically, however, kiore had a more sinister impact. They feasted on the eggs and chicks of seabirds, munched on native insects, and disrupted plant seed dispersal. While small, their presence marked the beginning of New Zealand’s rodent problem.

Second Wave: Norway and Ship Rats

Fast forward to the 1700s, and a second, more aggressive rodent invasion began. European explorers and traders unwittingly introduced Norway rats (Rattus norvegicus)-larger, more robust rodents that took hold in coastal areas and wetlands.

But it was the ship rat (Rattus rattus), arriving in the 1800s, that would prove the most damaging. Agile and tree-loving, these rats rapidly outcompeted both kiore and Norway rats. Thanks to the expansion of railways, they spread inland and upward-reaching into forests, climbing trees, and devastating bird nests.

Unlike kiore, ship rats could reach native birds where they were once safest-high in the canopy. Species like the kākā, mōhua, and kererū fell victim to these stealthy climbers. Entire ecosystems began to unravel.

Third Wave: House Mice Slip Through the Cracks

Smaller in size but no less problematic, house mice (Mus musculus) hitched rides with early settlers and became widespread across the country. Mice target invertebrates, native seeds, fungi, and small reptiles. On their own, they’re damaging-but when rats are removed or suppressed, mice populations often explode in what’s known as a "mesopredator release."

This makes pest control a delicate balancing act: one rodent down, another may rise.

How Do We Know All This?

Thanks to modern science, we now have an incredibly detailed picture of how rodents colonised Aotearoa. Ancient DNA analysis, radiocarbon dating, and archaeological studies have traced the movement of each species through time and geography.

• Landcare Research and Te Papa’s genetic studies confirmed kiore spread soon after human arrival-possibly within decades.
  
  

• Mitochondrial DNA from rat bones helped date the arrival of Norway and ship rats with remarkable accuracy.
  
  

• Findings from the Journal of Biogeography and New Zealand Journal of Ecology revealed surprising patterns-like how ship rats leapfrogged regions to settle in forest-rich areas quickly.
  
  

This science helps conservationists understand not just when rodents arrived-but how they continue to thrive, and what strategies might work best to manage them.

From Traplines to Modern Solutions

Rodent control in New Zealand isn’t new. Early settlers used rudimentary traps to protect food stores and livestock. But today, our goals are more ambitious: Predator Free 2050 aims to eliminate rats, stoats, and possums from the entire country.

At Connovation, we’re proud to support this vision with tools designed for precision, effectiveness, and environmental care:

• D-Block: A targeted, tasty bait designed specifically for rats.
  
  

• D Rat Trap Range: Engineered to last and handle extreme outdoor New Zealand environments, D-Rat traps work just as well around the house or in the shed. They’re suitable for all users - urban, rural, and professional trappers.
  
  

• Smooth Aniseed Lure: An aniseed scented and flavoured attractant proven to boost trap success, even in challenging environments.
  
  

By using science-backed products that work with New Zealand’s environment (not against it), we're helping frontline conservationists, community groups, and landowners take action that truly matters.

What You Can Do

The history of rodents in Aotearoa might be one of devastation-but the future can be different. Here's how you can help:

• Join or support a local trapping network.
  
  

• Use certified pest control products in your backyard.
  
  

• Educate others about the long-term effects of introduced predators.
  
  

• Stay informed: the more we know, the more effective we become.
  
  

Final Thought

"Every footprint tells a story - but some are better erased. Together, we can rewrite the next chapter for Aotearoa’s wildlife."