Rat Chat by Jude Gilbert
Environmental News Issue 25 Autumn 2011

With this wetter warm autumn on Barrier there has been huge food abundance in our bush which is good news for birds, lizards, and insects, but its also great for rats. The well documented bulge of autumn rats which has usually started to trail off by now remains high.

In the Windy Hill Rosalie Bay Catchment Trust sanctuary, however, we have had our lowest ever autumn results since we began using tracking tunnels to monitor for the presence of rats in 2004. This has been achieved with a single perimeter track using Pest-Off (Brodifacoum) and traps at 12.5 metre spacing, with our interior tracks using Rat-Abate in stations set 25m apart.

A key to the success of this mixed programme has been the input of our keen volunteers Brandan Kerr and Dave Harland. Brandon has checked bait and trap stations on the perimeter tracks weekly – which takes fourteen hours – and this has assisted to keep the rate of rat re-invasion into the sanctuary area down. Dave manages part of the Benthorn Farm project area and is also able to check traps on a weekly basis ensuring that they are continuing to catch well.

It seems that a mix of management tools with a high level of station checks has done the trick this autumn.

The current goal of the Trust is to find the most effective, cost-effective, and socially acceptable way of keeping pests at very low densities. It takes time to find this out as each method needs at least two years of operation before the efficacy can be assessed and seasonal variations and climatic events allowed for.

So far at Windy Hill we have trialled 6 years of trapping, 4 years of traps with short pulses of rat bait (Feracol-cholecalciferol), 18 months of Pest-Off (brodifacoum) bait, and a year of the less potent Rat-Abate (diphacenone) which is put out and replaced three times a year.

Trapping only has proven to be the least effective with a minimum of 30% and a maximum of 73% tracking tunnel percentages recorded. This has proven that toxins are required as part of any on-going pest management if we are to keep the rat and mice numbers low enough for the biodiversity to be sustained or improved. The Trust is working towards finding the least amount of toxin that can be used that combined with other methods still achieves a good result. We are close to finding that out – the Sanctuary rat tracking tunnel average for 2010 was 9% and the Control, or unmanaged area, stood at 76%. That represents a lot of rats that are not eating our precious native species in the Sanctuary.