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What's Happening up at Windy Hill? by Jude Gilbert


Can you imagine the size of a pile of 27,000 dead rats? Or 300 dead feral cats? That’s how many pests have been taken out of our ‘sanctuary’ area over the last seven years in the Windy Hill Rosalie Bay Catchment area. Imagine how many seeds, weta, lizards, paua slugs, birds eggs, and chicks those rats and cats would have eaten over that time.

The improvement in the biodiversity at Windy Hill and Benthorn Farm since integrated pest management began in 1999 is now really starting to show. To get to grips with what sort of difference our 3000 rats traps and 80 cats traps spread over 450 hectares was making, last year we set up a monitoring programme on land in the same area but not managed for pests as a comparison. In other words, a Control project. Over the year we monitored birds, rats, lizards, weta, and seedlings in the managed and unmanaged control area at the same time and in the same way.

Rat presence is measured using rat tracking tunnels—overnight pre-inked cards are placed inside 150 plastic tunnels set out at 50 metre spacings. A percentage is then calculated from the number of tunnels with rat prints versus the number without. In the managed area at Windy Hill the annual average indication of rat presence was 15% whilst the un-managed area recorded an average of 86%, topping at 100% in June. A huge difference.


Seedlings were counted and measured in eight one metre square plots—four in the managed and four in the un-managed area. In November 06 a total of 49 seedlings were recorded in the plots in the Control site and 87 in the plots at Windy Hill. Following a very dry summer when the count was undertaken again in April 07 both the control and the sites at Windy Hill had much reduced seedling totals —18 in the Control site and 47 at Windy Hill. Still a much higher number recorded in the managed site. Rats are quite selective with the seeds they enjoy so over a long period of time their consumption can really change the composition of a forest.

The difference with wetas and lizards was also marked between the managed and control site. Only 1 weta occupied one ‘motel’ for a single observation in the control area over the year with six weta motels occupied regularly in the managed area, with a total count of 40 weta. There were 17 ornate skink recorded in the lizard ‘motels’ in the managed area over the year and not one in the control site.

Bird densities need longer to assess for differences to emerge, however the second of the bird monitoring showed slightly higher densities in the managed area. The Control project is to be carried over for another year to further gauge the differences. What the control has shown to date, however, is that lower densities of rats improve the abundance of seedlings, weta, and lizards.

The size of the area we manage intensively for pests has continued to grow. What began as a twenty hectare site on one landholding in 1999 now involves twelve landowners working cooperatively with our Trust to manage 450 hectares. There are three project areas (as seen in the map below) which have over 60 kilometres of tracks with a rat trap every 12 or 25 metres—it takes three full time field workers, a volunteer, and a part time worker to manage the traps, maintain them and the tracks, monitor species, and protect the North Island robins which were re-introduced in 2004. The goal is to manage an area of 1000 hectares and in the long term, of course, to rid the Barrier of rats and feral cats..

As our expertise grows we are asked to trial equipment for manufacturers, to have Masters students (three to date) carry out their research here, and for organisations to set up species research within the project area Currently Landcare Research has over 200 rubber covers stapled to a wide range of trees to monitor for aboreal (tree dwelling) lizards. Little is known about lizards preferred habitat and this research hopes to see if an artificial ‘home’ might be preferred by lizards so they can be more easily studied.

To ensure we are achieving our goal of sustaining and enhancing biodiversity we constantly monitor. Last year we added monitoring for freshwater species to our programme. In our streams we find koura (freshwater crayfish), kokopu (native trout), shrimps, eels, and red finned bullies. Our results are sent off to NIWA who keep records of stream monitoring from all over NZ— the presence of native species indicates how healthy streams are and what species are surviving.
In 2005, following a review of the effectiveness of our trapping-only based programme we introduced a twice yearly pulse (a short hit) of toxins. With trapping alone it was not possible to get the rat tracking tunnel percentages below 30%; with toxin pulses the percentages have been as low as 1%. Rat numbers still rise and fall seasonally but since 2005 these averages have dropped considerably.

The pest projects managed by the Trust have provided a working model of conservation on private land and the conservation gains made through reducing rat and feral cat densities. Socially and economically the gain is the community’s—sustained full time employment and nearly $90k per year coming in wages. It is this same triple benefit—environmental, social, and economic —that the Great Barrier Island Charitable Trust sees as the result of achieving their vision of a rat and feral cat-free Great Barrier.