Black rat or roof rat (Rattus Rattus) in New Zealand

The black rat is also called the roof rat, ship rat, house rat

The roof rat is an introduce / invasive in New Zealand.

Found worldwide, adapts well to most climatic conditions. In New Zealand, it is the most commonly encountered rat species.

The roof rat is a natural climber, so will commonly be found nesting in an elevated position. Roof spaces and tree tops are common nesting sites. However it is also comfortable nesting on the ground and roof rat burrows are very common, often located under slab edges and flooring.

The roof rat is a prolific breeder and a female can have 5-10 young in a litter and up to 6 litters per year. They are happy to inter-breed within families. Social groups are often formed of multiple males and multiple females. One male tends to be dominant. Two to three females are often dominant to all other group members except the dominant male.  Lifespan in the wild is 12 to 18 months.

Colour: Variable – Black to light grey-brown with a lighter underside

Size range (adult):  Body 15-20 cm, Tail 18-25 cm, Weight: up to 350 g

The major distinguishing feature of the roof rat is the length of its tail – which is longer than the body. It has large ears and large feet. Both the tail and the feet help with climbing.

Roof rats are omnivorous and will eat a wide range of foods, including seeds, fruit, stems, leaves, fungi, and a variety of invertebrates and vertebrates. An adult will eat 15-30 g of food in a day.

• Roof rats produce 20-50 droppings per day, these are generally relatively narrow cylinders with pointed ends. Colour varies depending on diet.
• Because they consume and contaminate the food source during feeding, they can cause devastating damage to farms and livestock.
• They will always look for a ready food and water source along with warmth and shelter.
• If these are readily available, then the rat will not travel any great distance, however roof rats have been known to range up to 100 m or more from their harbourage if necessary.
• They will commonly use the same pathways from harbourage to food and water sources, leaving rub marks, urine trails and droppings to indicate these pathways.
• Roof Rats will be more active at night, when they feel more protected from predators. If seen during daylight, it tends to suggest a large population.

Roof rats will spread disease in various ways. Their urine and faeces will transport infections and their fur is recognised as being a carrier of several bacteria. Diseases of note include Leptospirosis, Salmonella, Hantavirus and others.

• Keep the property clean and tidy, limiting protected runways and potential harbourages. Keep vegetation trimmed and away from the building. Cut back overhanging tree branches.
• Close up potential entry points into a building.
• Eliminate or reduce accessible food and water. ie keep bins closed, do not leave pet foods out overnight and repair dripping taps or air conditioning.