Four types of wallaby – the dama or tammar, Parma, swamp and brush-tailed rock wallaby – are established on Kawau and today survive in large numbers throughout the island.
Located in the inner Hauraki Gulf, east of Warkworth, Kawau is a low lying island of about 2,000 hectares.
How they arrived in New Zealand
In about 1870, Sir George Grey, then Governor of New Zealand, liberated a variety of exotic birds and animals on the island, including wallabies. The wallabies thrived and became pests. Many other introduced species failed to survive, mainly due to a lack of vegetation caused by the wallabies.
Threat to Kawau Island's ecosystem
The effects of the wallabies' browsing can be seen everywhere and threaten Kawau’s significant ecological values.
There is little understorey in Kawau’s kanuka forests and few remaining patches of broadleaved forest. Heavy browsing stops anything from growing apart from tree ferns and introduced species like Arum lilies. In hard times wallabies even eat leaf litter so bare ground is common. Kawau’s native forest will not regenerate unless wallabies are either controlled to low densities or eradicated.
Wallabies could also be affecting Kawau’s North Island weka and kiwi populations. By removing seedlings and leaf litter, wallabies reduce food sources such as worms and insects for these birds. Kawau supports two thirds of the total population of North Island weka and is the last stronghold of this species.
The lack of forest understorey has also led to rapid storm-water runoff, erosion and loss of skeletal soils into the sea.
Wallaby control operations have been carried out on Kawau since 1923 with little success in curbing wallaby numbers or benefit to the island’s forest. Some landowners have managed to fence the animals out of their properties and seen big improvements in forest health in those areas.
Successful eradication programmes on nearby Rangitoto and Motutapu Islands, where there has been a marked forest re-growth, show it is possible to get rid of isolated groups of wallabies like those on Kawau.
Potential for ecological restoration
Once wallabies are gone, the potential for ecological restoration on Kawau would be huge. The forest under-storey would regenerate with richer soil and leaf layers. There would be more insect life and more food for kiwi and weka. Forest growth would also lead to more New Zealand wood pigeons, tui and kaka.
Possums could be removed once the wallabies are gone. This would benefit threatened species such as long-tailed bats and brown teal. It could also provide the opportunity to re-introduce native species lost from Kawau such as kokako, saddleback, robins and seabirds.
You can help
The Pohutukawa Trust New Zealand was established by private landowners in 1992 amid mounting public concern at the effects of wallabies and possums on the island's ecology.
The Trust's key objective is to rehabilitate the native flora and fauna of Kawau Island. To help achieve this, the trust aims to eradicate wallabies.
The Auckland Regional Council defines wallabies as animal pests in its Animal Pest Management Strategy and together with DOC are supporting the trust in this endeavour.