The Hirakimata Project

The Hirakimata Project

Hirakimata / Mount Hobson is of immense importance as a biodiversity hotspot and home to the main world colony of black petrels.

In 2016 Gt Barrier Environmental Trust led by John Ogden set up a comparative study to estimate rat abundance in two locations at the start of the Windy Canyon track and the summit of Hirakimata. Twenty Good Nature A24 multi-kill traps were fitted at each location during two seven week periods – December 2016 – February 2017 and March –April 2017. The traps are designed to instantaneously kill rats reaching up for the bait that allows the trap to reset itself automatically.

Rats were abundant in the first phase but were much reduced, especially on the summit, in the second phase. This ran counter to expected seasonal rat abundance trends. It was decided that the traps be left in place and the study repeated the following summer.

In the second year rat numbers were similar to those killed in year 1. Night photography was used to monitor rat behaviour around the A24 traps and often showed a reluctance to enter the baited area. Windy Hill Sanctuary used A24 traps for 2 1⁄2 years with disappointing results, leaving up to 30% of the rat population trap shy. They were deemed ineffective in lowering rat densities, performing worse than the classic snap traps. They have since been removed from Windy Hill and will be installed at Hirakimata between 2019 and 2020. Hirakimata with its montane podacarp forest is very different from Windy Hill's coastal broadleaf forest. Also, because of the reduced labour cost the effect on suppressing rodent numbers is valuable.

Auckland Council own the traps while the Department of Conservation will supply lures, gas canisters and staff time. In the meantime, a cat trapping program will continue in this area to protect taiko. 

Alison Walker