Controlling pests in New Zealand sanctuaries : varying the spatial distribution of the standard grid system in a mainland conservation project : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Science, Conservation Biology, Massey University, Auckland, New Zealand
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Date
2011
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Massey University
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Abstract
A toxin reduction study was carried out in the Waitakere Ranges, west of Auckland City,
New Zealand. The Auckland Council (previously called the Auckland Regional Council)
manage more than 20, 000 hectares (ha) of native ecosystems within the Waitakere ranges
using varying pest control methods and regimes. The ‘Ark in the Park’ (AiP) is part of this
20,000 ha protected habitat and it is intensely managed as a conservation reserve. AiP
employs volunteers, Auckland Council staff, researchers, contractors and a full time
project manager to monitor both pest and native species densities, deploy baits and traps,
and inform the public of the importance of active pest management. The use of toxins to
control pests can be controversial and decreasing poison usage and thereby reducing
potential by catch of non-target species is an important and under studied aspect of
conservation biology. In this study I tested the ability of pest control to meet targeted
rodent densities when the density of bait stations was significantly reduced.
The study area was a 333 ha block of native forest adjoining the existing AiP conservation
reserve, which at the time of the study represented 1200 ha of the Waitakere Ranges under
pest control. The aim of the study was to replicate the standard AiP pest control
methodology but reduce the density of poison bait stations. I then compared the density of
rodents achieved within this reduced toxin study area with two control sites, one without
rodent control and one with the standard rodent control methods used within AiP.
The existing AiP rat control methodology employs a 100 X 50 metre (m) grid of
bait stations, baited with pre-bagged Brodifacoum bait. In conjunction with
this, mustelid (Mustela spp) and feral cat (Felis catus) control is carried out utilising
existing track networks managed by the Auckland Council. In the current study this pest
control programme was altered by increasing the distance between stations from 50m to
100m giving a control grid of 100 X 100m. Along the perimeter of this research grid, a
150m wide buffer was installed where bait stations are placed in a 100 X 50m pattern to
reduce reinvasion of rats from non-pest controlled areas adjacent.
This study showed that at 100 X 100 m spacing overall rat density could be, as measured
by baited tracking cards, controlled to 3%, with 10% density at the perimeter and 0% in
the core of the area. As a direct result of this project additional areas under pest control
have now been added to AiP with a current total pest controlled area of 2500 ha. In
conclusion, this study has resulted in an additional 1200 ha of successfully pest controlled
area in the Waitakere Ranges using significantly less toxin for the initial knockdown,
lower costs, and less equipment and effort. It is recommended that future investigations
examine whether the required rodent control is able to be sustained over much longer
periods of time using the study technique trialled here.
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Keywords
Pest control baits, Pest control, Waitakere Ranges, Ark in the Park, Toxin reduction