Updated Wednesday 11 July 2018

Background

Zero Invasive Predators Ltd (ZIP), with the support of the Department of Conservation (DOC) and Predator Free 2050 Limited, is currently undertaking a programme of research and development work in the Perth River valley on the West Coast of the South Island.

The purpose of the work is to test and refine an approach to completely remove possums from large areas and prevent them from re-establishing, and to develop this approach for ship rats and stoats. We call the approach ‘Remove and Protect’. This is the first time such an attempt has been made on the New Zealand mainland. The results are expected to help enable New Zealand to achieve predator-free status by 2050. 

One component of the approach is the use of aerial 1080 to completely remove possums, using a method we developed in consultation with experts from the Department of Conservation (DOC), OSPRI and Manaaki Whenua - Landcare Research. We call this method ‘1080 to Zero’.

The DOC permission for ZIP to undertake an aerial 1080 operation in the Perth River research area acknowledged the risk to kea, and included a requirement that ZIP undertake a project to estimate how likely kea would be to consume bait containing 1080. This requirement was intended to assist DOC to assess and decide whether the application of toxic bait should proceed.

While kea have previously been monitored through aerial 1080 operations, as far as we know, this project is the first time that anyone has attempted to learn about the consumption of non-toxic baits by kea prior to toxic bait being sown. 

This Finding reports the results of the project. The work that is underway to measure and mitigate the risks to kea since this project was completed are described in a companion Update.

Kea and 1080

The Perth River research area contains kea, which are a nationally endangered alpine parrot. Unless the causes of decline are addressed, the national population of kea is expected to continue to decline by 50-70% over the next 10 years.

Predation is considered one of the key factors influencing that rate of decline. The kea’s ground-nesting habit and extended nesting cycle make them vulnerable to introduced mammalian predators, particularly stoats and, to a lesser degree, possums. Rats have occasionally been observed preying on kea eggs.  

Where predator control is undertaken, kea nesting success exceeds 70% compared with below 41% in non-stoat irruption years (non-mast years). In a recently-published paper, Kemp et al. (June 2018) report that the application of aerial 1080 improved the odds of kea daily nest survival at a treatment site by a factor of 9.1 during the two-year post-1080 period. 

However, kea are also known to have died as a result of 1080 poisoning. Of the 222 kea monitored by DOC (using radio transmitters) through 16 historical aerial 1080 operations between 2008 and 2016, 24 birds died as a result of 1080 poisoning. This equates to 10.8% (range: 7.1-15.7% [95% confidence interval]) of the total number of monitored birds. No kea deaths were recorded at 10 of the 16 operations. In operations where kea died, losses of between 5%-20% were typically observed (although one operation suffered a 41% loss of monitored birds). 

We have tried to minimise the exposure of kea to potential adverse impacts of the 1080 to Zero method by: 

  • Reducing the number of birds exposed to the method by reducing the size of the original proposed research area from c.20,000ha to 12,000ha (with a treatment area of 7,500ha).
  • Locating the research area as far as possible from the nearest kea scrounging site (Franz Josef township), which is 28km away at its closest point.
  • Choosing a site with a history of 1080 use (5 treatments since 1997), meaning that adult birds are likely to have been exposed to bait during previous operations.

We have also established systems to monitor the potential impact of the 1080 to Zero method by:

  • Fitting 30 birds with radio transmitters. The transmitters include mortality switches which send an alert if the transmitter is stationary for longer than 24 hours (indicating that the bird may be dead, or the transmitter has fallen off). In addition to monitoring any mortality, some of the transmitters should remain active for 2-3 years, which will enable survivorship and breeding success of adult females to be measured.
  • Undertaking a project to estimate how likely kea would be to consume bait containing 1080, so that the results could be used to inform decisions about sowing the toxic bait. The results of this project are described below. 

Method

The 1080 to Zero baiting schedule comprises sowing non-toxic ‘prefeed’ bait twice, in order to encourage possums and rats to treat the bait as a safe food source, before any toxic bait is applied.

The DOC permission for ZIP to apply aerial 1080 in the research area required ZIP to lace the second prefeed bait with the non-toxic biomarker pyranine. Pyranine fluoresces bright green under a UV blacklight, as shown in the images below, but does not dye baits green (i.e. the non-toxic baits did not resemble toxic baits). The purpose was to provide an early warning of the potential for kea to consume bait, and therefore be at risk of poisoning during the subsequent toxin operation. Proof-of-concept work had shown that, upon interaction with or consumption of this bait, the biomarker is visible externally on kea feet, beaks and vents, and in their scats.

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The first aerial application of prefeed was undertaken on 30-31 May 2018. The second, laced with pyranine, occurred on 21 June 2018. The baits were light brown in colour. The prefeed treatment area is shown on this map.

Immediately after the second application of prefeed was completed, we deployed one two-person team into known kea habitat to catch kea and observe them for evidence of pyranine. One team was deployed on the afternoon of 21 June, while four other teams were deployed on the afternoon of 22 June. The teams were in the area until midday on 23 June, when forecast inclement weather forced their exit. Kea catching locations are shown on this map.

All kea caught were checked for age, sex, and presence of radio transmitter and/or leg band. While under makeshift cover to create darkness, the feet, beak, and vent of each bird was examined by UV blacklight for green florescence indicating the presence of pyranine.

Results

The teams collectively caught and examined 11 kea for the presence of pyranine, with the following results:

  • 3 birds had no pyranine markings
  • 2 of the 3 birds that had no pyranine markings were adults
  • 8 birds had pyranine markings
  • 7 of the 8 birds that had pyranine markings were juveniles/sub-adults
  • 2 birds had markings on their beaks and vents, which indicated they had consumed the bait
  • 2 birds had markings on their beaks and feet only
  • 4 birds had markings on their feet only.

Details of the monitoring results are in the table below:

 1 Pyranine presence here suggests bait has been consumed.  2 Pyranine presence here suggests bait has been ‘played with’ or chewed, as a minimum.  3 Pyranine presence here suggests bait has been touched/held, as a minimum.

1 Pyranine presence here suggests bait has been consumed.

2 Pyranine presence here suggests bait has been ‘played with’ or chewed, as a minimum.

3 Pyranine presence here suggests bait has been touched/held, as a minimum.

The results do not tell us how much bait was consumed, or whether birds that had pyranine markings on their beaks or feet only (i.e. not on their vents) had consumed bait (but it had not yet passed through their digestive system) or would do so later.

The field teams also observed:

  • Other birds which they did not catch coming into contact with the bait
  • Kea scat which contained pyranine in the vicinity of ground/rocks where a small group of juvenile birds had been present
  • One bird playing with the bait in its mouth, but not consuming it
  • One kea moving between baits, which it would pick up, roll, then discard and move on to another bait.

Discussion

This project is the first time that anyone has attempted to learn about the consumption of baits by kea prior to the application of toxic bait. Consequently, there are no other results to compare to.

Overall, the results confirmed what was already known – i.e. that kea interact with bait – which is not surprising given the highly inquisitive nature of kea.

The small sample size (11 birds) significantly reduces the statistical power of the results to draw a clear conclusion about the level of likely actual interaction of kea with toxic bait. For example, the two birds of the sample that clearly consumed bait, i.e. 18% of the total, indicates a consumption rate for the actual population somewhere in the range of 2% to 52% (at the 95% confidence level). 

ZIP convened a workshop for a range of staff from ZIP, DOC, Predator Free 2050 Limited and Orillion (the bait manufacturer) on 27 June 2018, to consider the results of this project, and to identify any additional measures that could be taken to mitigate the potential impacts on kea of sowing aerial 1080. The measures that the workshop attendees considered had the most potential to mitigate the potential adverse impacts on kea of sowing aerial 1080 were, to:

  1. Consider the use of a kea repellent prior to sowing the toxic bait; and
  2. Attempt to distract kea from consuming toxic baits by providing fresh tahr as a more attractive alternative food source (given that kea have been seen to feed on tahr carcasses in the area)

Further details about these two measures are in a companion Update to this Finding.

 

Reference

Kemp JR, Mosen C, Elliott GP, Hunter CM. (2018). The effects of aerial poisoning for pest mammal control on the productivity of the kea (Nestor notabilis). New Zealand Journal of Ecology 42.