Hirakimata Rat Monitoring - phase 1
by John Ogden
The first phase of the Great Barrier Island Environmental Trust
pilot rat monitoring program on Hirakimata is now completed. Another
phase is currently underway, when rat numbers are expected to be higher.
Rats on Hirakimata are a serious threat to the
small populations of tomtit, robins and kakariki on the mountain, and
also to nesting Cook’s and black petrels. The results (Figure 1)
establish clearly that ship rats are just as abundant on Hirakimata
summit – in the black petrel nesting area – as they are at Windy Canyon
and elsewhere in the bush on Great Barrier Island. There is no
Figure 1: Overall results – numbers of rats killed over seven weeks
using 10 traps at each location. The columns are actual numbers and the
error bars are approximate standard errors.
Nearly all the rats were adults, with a slight
preponderance of males. Interestingly, the rats at Windy Canyon mostly
belong to the dark blackish morph of ship rat, while those on the summit
are predominantly the white- bellied form, but in all other respects the
populations show no differences. No kiore were caught at either
Unfortunately, the set-off counters purchased from
Goodnature with the traps proved unreliable, necessitating more days
climbing to the summit than anticipated. The addition of peanut butter
seems to make the traps more attractive to rats than the long-lasting
chocolate lures supplied.
As killing devices the A24 traps are effective
(Figure 2) and we are working with Goodnature on the counter problem for
Phase 2 of the program.
Figure 2: The A24 is a self-resetting multi-species kill trap targeting
rats and stoats. Attracted in by a long-life lure, once triggered, the
killed pests fall from the trap which resets up to 24 times for each gas
(CO2 ) canister. Source: Goodnature
If you’d like to be involved please call Alison
Walker, John Ogden or Kay Stowell or email(email@example.com)