Chew cards underline rat problem

July 2025

I have just run the second chew card exercise in line with the Pest Free Kaipātiki's 2025 chew card campaign. With the reduction in natural food in winter, predator species are more likely to interact with the baited chew cards and they are put out in reserves across the area to see how ongoing predator control has affected numbers. I wrote about the first chew card results at the new house in this linked blog post.

The chew card in the top bush

The idea is to put the cards out for three clear nights within a targeted fortnight and identify what had a chew on them from the teeth marks. My garden is long enough for 5 cards to be put out about 20 metres apart. When I put the cards out on Monday, it was the only forecasted dry spell in the fortnight. Naturally it rained every night at least for a time.

Since I started trapping at this new property, I have caught 11 rats in the northerly trap, mostly ship rats which are the agile climbers. It was no surprise that the chew card I fixed by the trap had been chewed. It was also not surprising that the card by the compost heap had also been chewed. I found a neat tunnel entrance in the grass clippings when I put the cards out, so someone has made themselves at home. The cards put out last year at those two points also got chewed. More surprisingly, the card mounted at the edge of the walkway by the main bush area had been eaten. Last October that card hadn't been touched. The two cards either side of the house were unmarked. Last year the first one had mouse teeth marks, but nothing this year.

There was no sign of crushing, which would indicate possums, and there was also no delicate removal of one side of the plastic to get to the bait, which is a sign of mice or invertebrates. It was basically rat decimation, especially on the most northerly card by the current trap, which had all the bait eaten out of it. Plastic littered the ground at all three of the chewed card sites, which cannot be good for the environment. I'll try and clear up as much as I can.

The chew card by the compost heap towards the top of the garden

Given I haven't caught anything in the southerly tunnel trap by the house, I think I need to move it, or another trap, up to target the bush area more effectively. That is not to say there aren't rats by the house. Something was loudly scurrying around above my son's room a few weeks ago and we put a lot of traps - mouse and rat - in the roof to try and catch it. Traps were triggered, but nothing got caught. However, the little clacking of claws overhead stopped, so I'll take that as a win.

Because it has been done at a different time of year, it's hard to say that the rat situation has got worse from the last chew card monitoring to this one. However, it underlines that I need to continue to trap if I want lizards and birds to be able to raise young safely in this garden. We've had tui and blackbirds successfully fledge offspring, but, given the number of birds visiting the garden and the habitat, I would expect there to be a wider range of nests. Rat numbers need to be under 5% for the birds to be able to thrive (that would mean none of the chew cards eaten). There's still a lot of work to do.