On Wednesday 18 March, ZIP worked with several members of the South Westland community to conduct a kea survey in and around the Perth River valley field site. The purpose of the survey was to provide additional information to help us more confidently estimate the effect of our 2019 predator removal operation on the local kea population.
Background
ZIP has been working in the Perth River valley since early 2018. At this site we are testing and refining an approach to completely remove possums, rats and stoats from large areas, and then prevent them from re-establishing, for the long-term, sustainable protection of native species such as kea.
When we began work in the Perth River valley, experienced kea catchers spent three days banding kea within the field site. During this work, they caught and banded 55 kea, and estimated a total population of 75-100 kea within the area.
In autumn/winter 2019, we carried out an initial predator removal in the 12,000 ha field site using a modified technique for applying aerial 1080. While we anticipated that the complete removal of predators would have significant long-term benefits for kea in the valley, we recognised the need to mitigate any potential risks to kea that this modified technique might present. In the months leading up to the predator removal operation, we worked with DOC and the Kea Conservation Trust to develop and deploy two new methods to protect kea during the operation (alongside a range of more standard risk mitigation measures that were already in place).
Prior to the operation, we exposed kea to non-toxic baits that mimicked the look and smell of toxic baits, containing the bird repellent anthraquinone. This bait was used to train kea to avoid cereal baits.
To attract kea to these aversion baits, we also placed tahr carcasses (repurposed from tahr control operations) at several sites above the altitudinal boundary of the operational area.
Our research confirmed that tahr carcasses are highly attractive to kea, and capable of drawing groups of kea to specific locations within the field site. So, in winter 2018, we field trialled the use of trail cameras lured with tahr carcasses to survey kea at several alpine locations within the site. The images gathered from this network of cameras suggested a similar population to the kea catchers’ estimate.
In late 2019, after we had completed the predator removal operation, we carried out another survey using camera traps lured with tahr carcasses, to help us understand the effect of the operation on the kea population. The numbers of kea seen on camera during this work were similar to those seen in winter 2018, suggesting that the initial impact of our predator removal operation on the kea population was likely to have been small.
The March 2020 survey
The March 2020 survey was carried out at eight locations (marked as blue dots on the map below) in and around the Perth River valley field site. Tahr carcasses were used to attract kea to each of the survey locations.
We were grateful to be supported on the day by Kaylyn and Marcus Pinney (Te Taho Deer Park/ New Zealand Deerstalkers Association), Ashley Cassin (Chair of the Glacier Country Tourism Group), Cliff Goodwin (Glacier Valley Eco Tours) and Su Sinclair (Project Support Manager, Predator Free 2050 Limited). Gus Gordon (Glacier Country Helicopters) helped us select the survey locations and place the tahr carcasses.
One of the eight alpine locations at which kea were surveyed (Joseph Arand)
At each of the survey locations, we worked with Kaylyn, Marcus, Ash, Cliff and Su to conduct five hourly kea counts, between 7:30am and 11:30am. Each time a kea was counted, we noted whether it was on the tahr carcass itself, or simply perched nearby. We also recorded any banded individuals we were able to identify, and synchronised the counts to minimise the chance of double counting birds.
A group of four kea photographed during the March 2020 kea survey (Briar Cook)
Over the course of the survey, between 25 and 39 kea were counted at the beginning of each hourly period (or an average of 30 per hour). This rate of sightings is similar to the rate at which kea were photographed by our trail cameras before the predator removal operation, and suggests that the number of kea now living in the valley is unlikely to have changed.
“It was a great experience to head up on the kea observation trip alongside Cliff Goodwin (owner/operator Glacier Valley Eco Tours). We were in an amazing spot and observed a good population of kea on our hourly inspections. With multiple locations observed at the same time, it was interesting to see the large numbers of kea that were present at certain sites.”
“It was interesting to discuss the ZIP program with [Science and Technical Ranger] Briar, and the ambitious nature of their plans. Being on the ground we could appreciate the scale of the area and how well the team has done to get the possum numbers down to just 3 animals. We appreciated the opportunity to see what is happening and we look forward to seeing how the project goes in the coming years.”
A juvenile kea spotted during the March 2020 kea survey (Marcus and Kaylyn Pinney)
Along with the many kea sightings our rangers enjoy while going about their work, helicopter pilot Gus Gordon’s recent estimate of 100-200 kea (based on the large numbers he has spotted while placing tahr for our survey and risk mitigation work), and the large collection of images captured by our trail cameras (including the one below), the results of this survey make us confident that there has been little change to this population.
A group of six juvenile kea caught on camera at a tahr carcass in August 2019
The relatively large population of kea in the valley can likely be attributed in part to a long history of predator control in the area. DOC has carried out five aerial 1080 operations here since 1997, which will have given several generations of kea an opportunity to breed successfully. Another factor is that these kea have had access to an abundance of nutrient-rich food in the form of tahr carcasses left by trophy hunters and by DOC’s tahr control operations.
The continued strong population of kea also suggests that the combined use of aversion bait and tahr carcasses has been largely successful in mitigating risks to kea from ZIP’s predator removal operation.
Seeing a healthy population of kea in the Perth River valley a year after our predator removal operation is hugely rewarding. We expect this population will continue to flourish as we learn to maintain an area free from the impact of possums, rats and stoats.
“The work ZIP’s doing in the Perth River valley is really necessary to help protect kea. These birds are intelligent, so we need to train them not to eat the baits while still getting rid of the rats, stoats and possums. ZIP has put a lot of work and thought into reducing risks to kea from 1080, and it’s been bloody awesome to see so many kea in the valley a year after their operation.”