On the rugged east coast of Great Barrier Island one family's predator control project demonstrates how trapping can reduce and suppress rodents so their recovering native forest can support more wildlife.
Each morning the eastern coastline of Aotea Great Barrier Island faces the rising sun of a new day and the vast empty expanses of the South Pacific Ocean. If you were to travel due east your next landfall would be near the city of Concepcion in Chile more than 9,200 km away. Aotea Great Barrier is an island literally standing at the edge of the eastern hemisphere.
This beautiful coastline is a mix of sweeping crescents of white sand, some like Kaitoke that are measured in kilometers and some like Awana that are tucked into smaller bays. Between these beaches with rolling surf and crystal clear water are rocky headlands with a smattering of small islets and offshore rock stacks.
It is also a coastline of two halves with the broad pastoral basin and estuarine harbour of Whangapoua to the north and the more populated locales of Claris, with its airfield, and Medlands, with its holiday homes, to the south. The rugged Okiwi Hill separates these two halves where the high centre of the island’s volcanic core reaches to the coast before plunging to the sea down steep ridges and spurs dissected by incised valleys carrying tumbling streams.
Once cleared for farmland, these steep exposed coastal slopes are now clothed in new native forest with remnants of the original bush remaining deep in the valleys. Forest regeneration is progressing at pace with the last of the grass being consumed by the forest despite the easterly gales that can lash the vegetation.
At the summit of Okiwi Hill, where the name Windy Canyon is a clue to the weather, a very ambitious predator control programme has been established on a property called Hiwitahi. Here the Walker family have dedicated themselves to threading tracks through the rugged terrain and developing an expansive network of traps to knockdown and suppress the rats and mice that ravage this landscape.
Looking east from Hiwitahi over Rakitu / Arid Island to the Pacific Ocean horizon.
Photo courtesy of Nik Walker
Their choice to focus their predator control on a trap network means the use of toxin with its risk of secondary poisoning of wildlife is negligible, a principled decision when the extensive use of poison would be so much easier in this topography. Since opening their private battle against predators in 2014 they have trapped over 2,300 rodents, they have more than doubled the area they are actively trapping and they have increased trap numbers to almost 200 trap stations.
They regularly catch around 400 rats per year. However when measured as catches per trap box their catch rate has declined from a summer peak of 1.75 rats per trap box per month in April 2014 to only twice exceeding 0.5 rats per trap box per month in April 2017 and March 2019. Their initial rodent population knockdown was dramatic through the 2014/15 summer and their persistent population suppression since then will be delivering sustained ecological benefits to their recovering forest.
Not only will native wildlife be facing significantly lower predation pressure during their annual breeding season they will also be benefiting from significantly lower food competition from rodents that would otherwise deplete the forest’s resources. This will mean that wildlife will likely be in better condition when they do breed and will have more food for young and juveniles that will further increase their chances of survival. In turn, wildlife moving into and around the property will increase seed dispersal meaning the diversity of the forest and the resources it can produce will also increase.
Ecology is a web of interconnected relationships between animals, plants and the landscape. Predation tears holes in this web but projects like Hiwitahi show how simple sustained predator trapping combined with determination as rugged as the terrain at the summit of the Okiwi Hill can repair the ecological fabric of recovering ecosystems so they can look forward to a future as bright as the morning sun rising over the vast empty expanses of the South Pacific Ocean on the beautiful east coast of Aotea Great Barrier Island.
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