Project maps and graphs

Maps used by volunteers, and graphs showing the results of predator control.Click on any of the images to view the page. Once expanded you can navigate via the arrows and index icon that will appear above the image.

Predator control

This shows the grid of bait lines, running in straight lines 100m apart. Bait stations are placed every 50m in most areas, but a 100m spacing is being trialled in some newer blocks. Cordons of stoat traps, all of which are kill-traps, also run through the area, and are being re-baited two-weekly all year (and sometimes once a week, at the time of peak stoat activity November to March).

(Click on image to see an enlarged view)

Rodent monitoring lines

Rodent monitoring lines

The effectiveness of rodent control is measured at intervals of around two months, from soon after baiting starts through to late summer. Tunnels with a peanut butter bait in the centre are placed in the localities shown above. Ink is applied to pads next to the bait, and as the rodent exits its footprints are picked up on blotting paper pieces that it has to cross.

A total of 190 tunnels are in place, in random positions, so that a variety of habitats are sampled. These are compared with 30 tunnels at three locations outside the Ark.

The protocol is to set the baits and papers on a day when there is little rain, and the papers are collected next day. Typically the incidence of rat footprints is around 2-5% in the Ark, and 70%+ outside.

(Click on image to see an enlarged view)

Monitoring results within the Ark: Before baiting and after

Predator control started early in 2003. The reduction in rat numbers has been spectacular - since 2007 the usual result of monitoring immediately after the Spring baiting is such that we would expect to find only one or two visited tunnels out of the 150 placed throughout the Ark. In March, around six months after the last baiting, and at the time of the natural peak for rat populations, the numbers are about 3 times higher, but still generally only 5 -8%.

The initial increase in mouse numbers was attributed to them flourishing in the absence of rats, but since 2006 their numbers have also dropped sharply - this was unexpected, but has been sustained and it now seems clear that the combination of broudifacoum and a 100m by 50m grid of bait stations is sufficient to significantly reduce mouse numbers. Click the forward arrow above to see the results for after baiting, only, which allows a more sensitive vertical axis.

(Click on image to see an enlarged view)

Monitoring results in Ark: after baiting started

monitor internal

This graph shows the same results as the previous page, but with the pre-baiting results excluded. The smaller vertical axis is now able to show variations more sensitively. Note the huge surge in numbers during 2014. By April and July 2015 this had been brought under control in the majority of the Ark, with the persisting positive tunnels largely from one area in the south. Furtherimprovement has followed with conversion of all 100m spacing areas in the south Ark to 50m spacing.

(Click on image to see an enlarged view)

Monitoring results outside the Ark

monitoring graph uncontrolled

The comparison between this and the results from within the Ark is striking confirmation of the effectiveness of the rodent control. Some of the variability shown above does not have an obvious explanation, but some can be explained in terms of the normal cycle of rat populations, where there is a large decrease in numbers during the winter, and a steady build up during the summer to a peak in late summer and autumn.

(Click on image to see an enlarged view)

Mustelid trap catch 12 months to July 2017

Ark catch map 2017

Every year, early Summer sees an explosion in the number of invading mustelids, as the females leave their nest and take their litter with them. Regularly there is a concentration of catches on the periphery, but this year there has been a higher presence in the internal areas. The reason for this is not apparent, as there is not a similar pattern in rat presence.

Stoat catch by month 2004-2008

Stoat catch by month 2004-2008

The parameter shown is catch per trap - the number of traps has risen steadily throughout the period, so catch per trap corrects for the effect of this increase on actual numbers caught.

There is a consistent increase in numbers in mid-summer, when the female stoats come off their nests with their brood of around eight offspring. In two years (04-05 and 06-07) this produced a very large peak in December/January, but in the other two years there was a much less marked increase, spread evenly from December to February. It is not clear why there was this change in pattern - in 05-06 there was a bigger catch in the preceding Autumn, which could explain lower breeding in Spring, however 04-05 and 06-07 had similar patterns for most of the year but very different results in December/January.

Traps are checked and re-baited less often in winter and more often in summer - for most of them the frequency is two-weekly and weekly, respectively. The bait used for most is rabbit meat, with a cracked egg as well (especially important in summer, when meat rapidly deteriorates), but for some a rabbit paste is used.

All traps used are kill-traps (DOC 200, or GoodNature)

Whitehead Survey 2012

Whitehead survey 2012.jpeg

Here are the results of the 2012 survey. Map produced, using Quantum GIS software, by Laurence Bechet, with assistance from Cameron Wilson.

Whitehead Survey 2013


Whitehead observations 2013


Rat catch early 2013

rat catch early 2013

There is evidence of post-baiting population in two sections of the internal part of the Ark, one in the north and one in the south. These are indicated by red markers ie persistence is interpreted as March catch, or monitoring tunnel prints - a catch in February which did not repeat in March can be regarded as showing response to baiting. Comparing this with the previous map, the northern area is new, but the southern one is possibly a continuation from mid-2012.

Rat presence early 2014

Rat presence 0214

Monitoring tunnels were checked in February, and the position of tunnels with footprints is shown, along with the rat catch in mustelid traps for the few weeks before.

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