Ability to nest in trees, attics, & high structures makes rats a persistent challenge for conservation efforts & pest management professionals.
Summary of PMANZ Article by Peter Barry
Introduction
The roof rat (Rattus rattus), also known as the black rat or ship rat, is one of New Zealand’s most widespread and destructive rodent species. Introduced via European ships in the 19th century, these agile climbers thrive in urban, rural, and forest environments, posing serious ecological, economic, and health risks. Their ability to nest in trees, attics, and high structures makes them a persistent challenge for both conservation efforts and pest management professionals.
Identification
Roof rats are sleek and slender, measuring 16-24 cm (excluding their long tails, which are longer than their bodies).
They have:
- Large ears & a pointed snout
- Smooth black to brownish-grey fur
- Excellent climbing ability, allowing them to access elevated areas such as roofs, ceilings, and dense vegetation
Habitat & Behaviour
These highly adaptable rodents nest in trees, buildings, and dense foliage and are primarily nocturnal. Their omnivorous diet includes fruits, seeds, insects, bird eggs, and small vertebrates. Social and territorial, roof rats communicate through vocalizations, scent marking, and physical interaction. Their rapid reproduction—up to five litters per year—makes controlling their populations a constant challenge.
Impact on NZ’s Ecosystem
Roof rats are one of the greatest threats to New Zealand’s native wildlife. As expert climbers, they raid nests, consuming eggs and chicks, contributing to the decline of endangered birds like the kōkako, kākā, and New Zealand robin. Their presence has led to the extinction of native species such as the bush wren and huia.
In addition to predation, they:
- Compete with native species for food and habitat
- Disrupt forest regeneration by consuming native seeds and young shoots
- Invade previously rat-free islands by swimming long distances, devastating local ecosystems
Economic & Health Risks
Beyond their environmental impact, roof rats pose serious risks to public health and infrastructure:
- Carriers of diseases such as leptospirosis, salmonellosis, and rat-bite fever
- Contaminate food supplies in homes, warehouses, and food storage facilities
- Cause costly structural damage by gnawing on electrical wiring, insulation, and wood—increasing fire risks
Control & Management Strategies
Effective pest management is critical to controlling roof rat populations. A combination of habitat modification, trapping, baiting, and community involvement can help reduce their numbers.
1. Habitat Modification
✅ Securely store food waste, pet food, and livestock feed
✅ Seal entry points in buildings (cracks, vents, gaps in roofing)
✅ Remove overgrown vegetation, woodpiles, and debris that provide shelter
2. Trapping & Baiting
✅ Snap traps & live traps are effective for monitoring and controlling small populations
✅ Rodenticides (e.g., brodifacoum, bromadiolone) should be used cautiously to prevent harm to non-target species
✅ Bait stations should be placed along rodent pathways and high-activity areas
3. Community Involvement
✅ Public awareness campaigns educate residents on prevention and control
✅ Community-led trapping programs have successfully reduced rat populations, particularly in conservation areas
4. Island Eradication Programs
New Zealand has been a global leader in island pest eradication, successfully removing roof rats from several offshore islands. These projects involve:
✅ Intensive baiting & trapping
✅ Strict biosecurity measures to prevent reinfestation
Conclusion
The roof rat remains a persistent threat to New Zealand’s environment, economy, and public health. Through integrated pest management, community participation, and ongoing vigilance, significant progress can be made in controlling their populations and protecting native ecosystems.
PMANZ 
PMANZ is an association run by pest managers for pest managers. The association was formed in 1976 to provide a unified voice when important issues arose that required our industry’s input.
The Pest Management Association of New Zealand (PMANZ) is a leading organization dedicated to promoting effective pest management practices across the country. Comprised of professional pest control companies, PMANZ strives to protect the health, environment, and economic well-being of New Zealand through the responsible management of pests. With a commitment to sustainability, PMANZ emphasizes the use of safe and environmentally friendly pest control methods. Through education, training, and advocacy, the association ensures its members are equipped with the latest knowledge and techniques to tackle pest infestations efficiently. PMANZ is a trusted resource for individuals and businesses seeking reliable pest management services in New Zealand.
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