Councils reduce pest monitoring costs with chewcards
A chewcard mounted on a tree with the bait placement illustrated. - Peter Sweetapple
Chewcards are 18 cm × 9 cm pieces of plastic coreboard with palatable bait, such as peanut butter, pressed into the channels in the boards (see photos), which are used for monitoring the distribution and abundance of a range of pests, most commonly possums. They were developed in 2005 by Peter Sweetapple and Graham Nugent at Landcare Research as a simple and cheap alternative to existing tools (traps and tracking tunnels) for monitoring a range of pest species, and can show what species of small mammal pests are present by the tooth impressions made by pests that chew the cards.
For possum monitoring a major advantage of chewcards over traditional monitoring using leg-hold traps is their lightness (about 20 g each when baited, compared to about 400 g for a trap), so field workers are not limited by the number of chewcards they can carry. A second major advantage is that, unlike leg-hold traps, chewcards do not need to be checked every day, so they can be set for a week (or more) and only require two site visits (to set out and recover them) instead of the usual four visits for traps.
The Hawke’s Bay Regional Council was an early adopter of chewcards for possum monitoring. It has about 650 000 ha, mainly farmland, under possum control, with possum abundance assessed across about 10% of this area each year. Council staff asked Peter in 2010 how they could use chewcards to reduce their monitoring costs. As a result, chewcards have replaced trapping for about 80% of this council’s possum monitoring and have enabled a significantly expanded monitoring programme while reducing costs to ratepayers by about 50%.
To gauge the extent of chewcard use in other regions, Peter recently sent a short questionnaire to 12 councils and received eight replies. Four indicated that they used chewcards to some extent to complement other monitoring methods, with one other council having trialled them once. The main reasons cited by these four councils for using chewcards were low cost (four responses) and ease of use (three responses). Other reasons included the high acceptance of chewcards by possums, their acceptance by multiple pest species and, for one council, the availability of good interpretation resources.
Only Hawke’s Bay Regional Council used chewcards solely for monitoring possums, while all other councils were interested in monitoring multiple pest species. Interestingly, it was this ability to monitor multiple species that prompted some councils not to use chewcards, because they perceived that high rodent detection rates were likely to have a negative effect on either possum detection or ease of interpretation of results. Two councils supplied chewcards to the public for citizen science or community group initiatives.
As a result of the increasing use of chewcards, the National Pest Control Agencies (NPCA) have recently developed a standard protocol for how to use chewcards for possum monitoring and have included this in their publication A1 Possum Population Monitoring (2015). This official recognition of the chewcard method and the commercial production of chewcards (by Connovation and Pest Control Research) will probably lead to greater uptake by territorial authorities in the future.*
This work was funded by TBfree New Zealand, the Ministry of Business, Innovation and Employment (through its Envirolink scheme) and Landcare Research.
Peter Sweetapple, Graham Nugent
* Note: This document is no longer available from the NPCA website, but will shortly be loaded onto the Bionet (http://bionet.nz/) site.
