the roof rat still raiding NZ's native bird colonies

Size
Length: 15–22 cm, Weight: 120–200 g
Lifespan
1–2 years
Diet
An opportunistic omnivore; they are the primary predators of forest birds, consuming eggs, chicks, fruit, and large quantities of native invertebrates.
Habitat
Arboreal and versatile; they are skilled climbers that spend much of their time in the forest canopy, nesting in tree holes, epiphytes, and ceilings.
Range
Ubiquitous throughout mainland New Zealand and many islands; they are the most common rat found in native forests and bush-clad residential areas.
Endemism
Invasive
Main Threats
The focus of massive, landscape-scale predator control programmes using traps and toxins to prevent the collapse of native bird populations.
Population
Ship rats are the dominant rodent in the New Zealand bush, and their numbers can skyrocket during "mast" years when forest trees produce an abundance of seed.
Conservation Status
Introduced
High in the canopy of a New Zealand beech forest, a silent and agile shadow moves with a grace that belies its destructive nature. The ship rat is the "aerial assassin" of the native bush, a creature that has traded the burrowing life of its ancestors for a life of three-dimensional dominance. With a tail that acts as a sophisticated balancing pole and large, translucent ears that catch the faintest rustle of a nesting bird, they are perfectly adapted for life in the treetops. Unlike the ground-dwelling Norway rat, the ship rat views the forest canopy as its personal pantry, making it the most significant driver of decline for many of our iconic forest-dwelling species. The impact of their presence is a quiet tragedy that plays out every night across the country. They are "sampling" predators, moving through the branches and investigating every cavity and fork for the protein-rich prize of a bellbird egg or a sleeping wētā. Their ability to climb almost vertical surfaces means that no nest is truly safe, regardless of how high it is positioned. This relentless pressure has forced a fundamental shift in the behaviour of many native animals, yet for many, the ship rat remains an insurmountable threat. They are the primary reason why many of our birds can now only be found on predator-free offshore islands. Beyond their appetite for meat, they are major consumers of forest seeds and fruit, effectively competing with the kererū and other native birds for the resources needed to survive the winter. By eating the seeds before they can germinate, they are also altering the future composition of the forest itself, ensuring that the next generation of trees is dictated by rodent preference rather than natural succession. They are a biological "bottleneck," squeezing the life out of the ecosystem from multiple directions simultaneously. Their rapid breeding cycle ensures that even after a successful control operation, their numbers can rebound with terrifying speed. To see a ship rat in the light is to witness a creature of intense, nervous energy. They are perpetually in motion, their dark, bulging eyes searching for the next opportunity or the next threat. They represent the ultimate challenge for the "Predator Free 2050" goal—a widespread, intelligent, and highly mobile enemy that has integrated itself into every level of the New Zealand environment. They are the "black ghosts" of the ngahere, a reminder that the beauty of our forests is currently under a state of constant, nocturnal siege.