The ship rat, which is more common, has a tail larger than its body and ears that cover the eyes when pressed forward. Also known as the black rat, this rat is the deadliest predator of New Zealand’s native birds. An expert tree climber, it was first seen in New Zealand in 1862 and the disappearance of large populations of saddleback, stitchbird and bellbird immediately followed. Both of the European species are associated with human activity and are found in houses, tips, waterways and cropland.
For larger birds, such as the kiwi, rats are not a predator but a competitor because the invertebrate diet of rats and kiwi is almost identical; both forage for surface invertebrates. In autumn and winter ship rats spend more time on the ground and the intake of invertebrates is high and plant material low. In summer ground is harder to probe and more insects are taken from the surface. Young kiwi have short bills and depend on surface insects. Competition from rats slows the growth rate of kiwi chicks therefore they take longer to reach the weight of one kilogram when they are safe from stoat predation.
Did you know? In a kiwi territory there may be over 100 rats.