Last year, ZIP began developing and testing two methods to mitigate potential risks to kea (Nestor notabilis) from a proposed aerial 1080 operation to remove predators from the Perth River valley, South Westland. The two methods are to:
apply non-toxic bait laced with bird repellent to deter kea from eating the toxic bait; and
provide fresh tahr carcasses as a more attractive, preferred, food source.
This Finding, and the accompanying Technical Report, outlines two trials we ran between June and November 2018, to (i) investigate whether kea activity is higher around tahr carcasses than at cereal bait (Phase 1), and (ii) increase our confidence in tahr carcasses as a technique to mitigate the potential risk to kea from the proposed 1080 to Zero operation (Phase 2).
The trials covered a broad range of topics, including the population demographics of kea seen at tahr carcasses and at bait, types of kea behavioural interactions seen with cereal bait, proportion of the banded population of kea visiting these sites, and average longevity of tahr carcasses as a food source for kea.
Investigating whether kea activity is higher around tahr carcasses than at cereal bait piles
This trial consisted of three separate deployments of nanny tahr carcasses at sites above the Perth River valley bush line, between June and August 2018. Tahr were placed at 21 sites during the first deployment, but an increasing avalanche risk towards the end of winter 2018 made it necessary to reduce the number of sites during the second and third deployments (to 15 and 9, respectively).
Alongside each carcass, we hand-laid a 1.5 kilogram pile of green-dyed, non-toxic, cereal bait, laced with the secondary bird repellent anthraquinone.
Two trail cameras were used to monitor kea at each site. One camera was positioned to record kea activity on and around the tahr carcass, and another was positioned to record kea activity at the bait. Both cameras were set with a time delay of 5 seconds between each trigger event. Tahr carcass cameras were set to record one image per trigger, and bait cameras were set to record videos of 10 seconds duration, in order to enable detailed examination of how kea interacted with the repellent-laced cereal baits. Images from the Browning cameras used in this trial were clear enough for us to identify individual kea based on their leg bands. The cameras were serviced six times, every 7 to 10 days, depending largely on weather conditions.
What did we observe?
The average number of images of kea recorded per day during service 6 (the most complete set of camera data) totalled 6,821 for the tahr carcass cameras and 1,171 images for the bait cameras – a ratio of 6:1. This suggests that tahr are more attractive to kea than cereal baits.
The different types of interactions kea had with bait were also recorded during the camera footage analysis. A range of behaviours were recorded at all bait sites, including visual inspection, touching, picking up, and not interacting with baits. During service 6, consumption of bait was recorded at 4 of the 9 sites. Consumption was generally followed by behaviours that indicated the birds had experienced the effects of the anthraquinone repellent, such as gaping, head shaking, fluffed feathers, beak wiping and vomiting upon tasting bait.
During Phase 1, we recorded 31 of the 55 banded Perth River valley kea at tahr carcasses. Using mark-recapture analysis we were able to estimate a population of 59 kea [95% CI 46-86%] visiting tahr carcass sites, which is in line with the estimated population of 75-100 birds within the Perth River valley.
Each tahr carcass was found, on average, to last for no more than 7 days before being completely stripped of meat.
Refining the deployment of tahr carcasses as a technique to mitigate the potential risk to kea in the Perth River valley
Between November and December 2018 we ran a second trial to more rigorously assess the attractiveness of tahr carcasses in relation to cereal baits; and to refine the deployment of tahr carcasses as a technique to mitigate risks to kea from the predator removal operation.
The first trial consisted of two rounds of tahr and bait deployment carried out across 11 sites. This trial was designed as a “mixed choice” test, whereby birds could choose to visit sites that had both a tahr carcass and a pile of bait, or sites that had a pile of bait only. For the first round of this trial, five of the sites were initially set-up with a tahr carcass and a 1.5 kilogram pile of cereal bait, five other sites comprised bait only, and one site was a bait-only control site. For the second round, the initial carcass/bait and bait-only sites were swapped, to try to ensure that any kea visits then were less influenced by their memory of the set-up during the first round. The control (bait only) site was set-up and retained at the same site for each round, in the event that kea showed a substantial change in behaviour towards bait only sites (which were formerly carcass/bait sites in round 1), which could be attributed to the memory of tahr carcasses at these sites.
We used RS5, cinnamon-lured, bait with no dye and no repellent, in order to remove any cues that kea could relate to the anthraquinone-laced repellent bait used in Phase 1 (i.e. Wanganui #7, dyed green, with a double-dose of orange-scented lure). RS5 was not used during the two prefeeds that ZIP sowed at the Perth River valley site in May and June 2018.
Browning trail cameras were used to monitor bird activity at all 11 sites. Two cameras were deployed at the carcass/bait sites (one to record kea activity on and around the tahr carcass, and the other to record kea activity at the bait), and one camera at each bait-only site. The cameras were deployed for a total of 14 days during the first round, and for 10 days during the second round; the different periods reflected the influence of weather on our ability to access the cameras. All cameras were set to take one image per trigger, with a 5 second delay; in order to obtain the most direct comparison of kea activity between sites. All cameras were programmed to take images rather than videos because Phase 2 was focussed on kea activity between site types, rather than a close examination of interaction types. One SD card failed at a tahr carcass during round 1, so this site was not included in the results.
We compared the average number of images of kea – i.e. all birds, both banded and un-banded – on tahr carcasses, bait at paired sites, and bait-only sites (including the control site). We also recorded banded individuals seen at each type of site, for each round.
What did we observe?
During round 1, cameras captured an average of 646.4 images of kea at tahr carcasses and 53.8 images at bait at the carcass/bait sites, and 4.6 images of kea at the bait-only sites per operational camera trap day. During round 2, cameras captured an average of 464.7 images of kea at tahr carcasses and 46.6 images at bait at the carcass/bait sites, and 3.7 images of kea at the bait-only sites, per operational camera trap day.
The control (bait only) site captured an average of 13.8 kea images in round 1, and 5.9 kea images in round 2, per operational trap day.
The average number of kea images captured at tahr carcasses and bait at the carcass/bait sites and at bait-only sites (corrected for varying camera deployment days in the two rounds) is shown in Figure 4. In round 1 the ratio of kea images captured on tahr carcasses to all bait sites (including the control site) was 5:1, and in round 2 the ratio was 8.3:1.
In total, 17 individual banded birds were recorded, three of which had not been seen during Phase 1.
These trials have demonstrated that tahr carcasses are indeed a food source that kea find highly attractive, which may be unsurprising given past anecdotal accounts, but until now had not been quantified. Birds will not continue to be active at a site where a tahr carcass is no longer present.
The results do not provide evidence to substantiate two important concerns about the potential impact of the proposed Perth River Valley 1080 to Zero operation on kea, i.e. that increased availability and repeated exposure of tahr carcasses may bring kea from outside of the Perth River Valley, or that the increased availability and repeated exposure of cereal bait raises the risk of cereal bait consumption by kea.
Sites containing tahr carcasses and bait were found to be more attractive than bait-only sites. Providing a highly attractive food source (i.e. tahr carcasses) to the local population of kea in the Perth River valley will enable us to expose kea to repellent-laced cereal bait. We also learned that bait laced with approximately 1.5% by weight of anthraquinone bird repellent will induce behaviours in wild kea consistent with those observed during recent captive trials with anthraquinone-laced bait (at a concentration of 2.7% anthraquinone). Consequently, we propose to make aversion training (repellent) bait available at multiple tahr carcass sites at a higher altitude than the treatment area of the proposed 1080 to Zero operation both prior to and throughout the operation.
The trials also provided other useful information that helps to answer the fundamental questions that underlie our efforts to mitigate the potential risk to kea from being poisoned as a result of consuming 1080 baits, including that:
A tahr carcass will last for approximately 7 days before kea consumption reduces it to a skeleton.
It is possible to reliably identify individual birds through band information seen on camera trap footage with the Browning camera trap model, which enables us to better understand the demographics of the kea population.
While it is not possible to guarantee zero mortality of non-target species during any predator control operation, we are hopeful that these measures will reduce potential consumption of toxin-laced cereal bait, and therefore mitigate the risk to kea in the Perth River valley.
Want to learn more?
Check out the technical report.