Zero Invasive Predators is conducting a trial predator removal operation in the Perth River valley in South Westland, which aims to remove all possums, and potentially rats, from 12,000 hectares of rugged back country.
If successful, this trial will provide important information about how 1080 can be used to completely remove predators from a large mainland area.
The Perth River valley is a mountainous area that contains a population of 75-100 kea. Predator removal operations that use 1080 are known to benefit kea populations, but these operations can kill individual kea if they eat toxic bait. With advice from kea experts at the Department of Conservation and the Kea Conservation Trust, ZIP has implemented measures to mitigate the potential risk to kea from the operation, including applying non-toxic cereal baits containing a bird repellent prior to the operation to ‘train’ kea to avoid baits, and distributing a small number of tahr carcasses above the operational area, to attract kea away from toxic baits.
We are also monitoring kea survivorship before, during and after the operation.
Between 12 February and 9 March 2018, 29 kea were fitted with transmitters to monitor their survivorship through the planned 2018 aerial operation. This included 19 adults (12 female and 7 male), and 10 juveniles. In June 2018, one additional adult female kea was fitted with a transmitter, bringing the sample up to 30.
The transmitters are fixed to kea in a way that is designed to be relatively secure, while allowing them to move freely and behave naturally.
Monitoring is carried out using the Sky Ranger system, whereby a light aircraft fitted with radio receivers flies over the area and records the location and status of each transmitter.
The results of all of the Sky Ranger monitoring we have completed to date are shown in the table below.
The most recent Sky Ranger monitoring has determined that 13 of the 30 kea are still in the Perth River valley. Seven kea are in undetectable locations (either outside the area or in a location where the transmitter is unable to communicate with the Sky Ranger system), and ten of the remaining transmitters are now in ‘static mode’, indicating that either they have fallen off, or the kea wearing them have died.
Interestingly, two of the kea whose transmitters are in static mode have since been seen on camera, identifiable by their leg bands (pictured below, with leg bands circled in orange – click on the images to enlarge). This confirms that in at least two cases, the static signal represents a dropped transmitter.
One more Sky Ranger flight will be made on the day that toxic bait is applied in the Perth River valley, to confirm the number of kea in the operational area at that time.
Most of the kea in the Perth River valley have been wearing transmitters for over a year.
They are wild birds, and so we did not expect that all of them would remain in the valley. Other kea monitoring projects have witnessed a similar ratio of birds leaving the area or dropping their transmitters.
We will continue to monitor kea in the valley throughout the predator removal operation, and then through the following breeding season.
In the longer term, we expect that mark-recapture analysis of camera footage of the 55 kea in the valley fitted with leg bands will enable us to build a fuller picture of the outcome for kea in the Perth River valley.
We will continue to report the results of our research on our website.