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2022
An ArcGIS StoryMap
From Friday 1 July, the Te Manahuna Aoraki Project Board engaged ZIP to lead the development and implementation components of Te Manahuna Aoraki Project.
This is a significant milestone for all of our team, but especially for our newest members who have joined us from previous roles with our partner, the Department of Conservation (DOC). We are excited to welcome Adriana Theobald, Chloe Underwood, Doug Rands, Jolene O’Connor, Julia Gibson, Simone Smits, Tom Smits, and Geoff ‘Woody’ Woodhouse to ZIP.
Te Manahuna Aoraki Project is a partnership between mana whenua, the Department of Conservation, NEXT Foundation, Toitū te Whenua Land Information New Zealand, high country landowners, and other philanthropists and government agencies.
The project launched in 2018, with the vision to protect and revitalise the upper Mackenzie Basin and Aoraki Mount Cook National Park so native animals and plants can thrive. The 310,000 hectare project area includes mountain ranges, dryland tussock grasslands, Lake Pūkaki, Lake Takapō/Tekapo and the extensive braided river systems that feed them. The area is home to an extraordinary range of native birds, plants, reptiles and invertebrates – from New Zealand’s rarest wading bird, the kakī, to the endangered robust grasshopper.
This is an exciting time for ZIP, and we are thrilled by the opportunity to take on new skills, experience and pest elimination challenges across this diverse and spectacular landscape.
Over the next year, we will work to expand the alpine predator elimination in the Malte Brun Range, and turn our attention to eliminating other key threats to native species.
Keep an eye out for updates here, and on the Te Manahuna Aoraki Project website, Facebook and Instagram.
ZIP’s predator elimination model involves removing predators from a specific area and then protecting it from reinvasion. After the elimination operation, we intensely monitor the area and quickly respond to any predator detections using a range of techniques, one of which is the targeted application of aerial 1080 around the detection site.
Native birds in the Perth River Valley are recovering just as well in areas that have had one or more of these localised aerial treatments, when compared to surrounding areas that were only treated during the main elimination operation.
Earlier this year we reported positive signs of bird recovery in the Perth River Valley following our operation to eliminate possums, rats and stoats. In this update, we take a closer look at how this recovery looks in areas of the valley that have received different numbers of toxin applications. This work is part of the Predator Free South Westland project.
Setting up a trail camera. A MotoLure that dispenses mayonnaise is placed in the camera’s field of view to attract predators. Photo by Chad Cottle.
In 2019 we removed over 99% of predators in the Perth River Valley by applying aerial 1080 bait to all potential habitat in an elimination operation. We always anticipated that some predators might survive the operation or could reinvade the area over time; after all, an elimination approach requires us to protect the conservation gains we make. Our network of 142 lured trail cameras helps us detect these individuals so we can respond quickly to remove them.
Possums sneaking a snack of mayonnaise are caught in the act by a trail camera.
Usually, our first response to a predator detection is a ground-based operation using bait stations, traps and detection dogs. In some cases, however, the terrain makes this approach impractical and/or a ground-based response is not enough to prevent the emergent predators from spreading. When this happens, we use an aerial treatment of 1080 bait precisely targeted to the localised area where predators have been detected. The confluence of the Perth and Barlow Rivers seems to be particularly prone to reinvasion of rats from across the Barlow River, and has been treated on numerous occasions over the past three years (shaded dark grey in the map below).
Perth River Valley predator elimination project area. Grey shading shows the frequency of localised aerial treatments since 2019. Each dot represents a trail camera set up in front of a lure dispenser.
We sometimes get asked if this use of localised aerial treatments is slowing the recovery of native birds present in the Perth River Valley site. There is plenty of scientific evidence that native bird populations do better when predators are controlled (see references, below). Here, we investigated our camera network to see if there was any difference in native bird recovery between areas that had been treated multiple times and areas that only received the initial elimination treatment. Although trail cameras are primarily used to detect predators, they also detect native birds that happen to pass by. When we compare the proportion of cameras that detect birds, at the same sites, over time, we can get an indication of the relative size of these populations.
We looked at three species— kea, kakaruai/South Island robin, and ngirungiru/South Island tomtit. These species are known to be vulnerable to predation and we therefore expect their populations to recover when predators are removed. They are also the species that spend a lot of time on the forest floor and, because the cameras are low to the ground, are detected most consistently. We know that detections fluctuate over the year, peaking in summer with new fledglings. By comparing two late summer months, these seasonal variations are minimised.
We compared the number of cameras that detected birds in January 2020 (one month before any localised treatments took place) with February 2022 (one month after the most recent treatment for which we have analysed data) in areas that had received either none, between one and two, and three or more localised treatments.
Trail camera detections in January 2020 and February 2022 of kea, kakaruai/South Island robin, and ngirungiru /South Island tomtit in areas of the Perth River Valley that have received different numbers of aerial treatments. Numbers of cameras in each area ranged: 0 treatments, n=25; 1-2 treatments, n=54; and 3+ treatments, n=42
In areas that have received localised aerial treatments, more cameras are detecting kea and ngirungiru than two years ago. Kakaruai detections have remained reasonably stable, which is not surprising given the relatively low number of detections. The very low numbers (or lack) of species detections in areas that have not been treated beyond the initial elimination operation was surprising. However, this result may be explained in part by the habitat type most of these cameras were in (higher altitude in some cases, and the narrow, colder Upper Perth River Valley) where we would expect to find fewer native birds. Across the whole Valley, predator numbers are close to zero, so predation is unlikely to be a factor.
These camera detection results support the increase in birdlife that our field team are seeing and experiencing first-hand. Native bird populations continue to recover in the Perth River Valley, and the localised treatments to maintain predator freedom are not hindering that recovery.
A pair of kea show off in front of a lured trail camera, June 2022
Acknowledgements
Thank you to Matt Hickson of the Department of Conservation for a review of an earlier draft of this update.
References
Kemp, J. R., Mosen, C. C., Elliott, G. P., & Hunter, C. M. (2018). Effects of the aerial application of 1080 to control pest mammals on kea reproductive success. New Zealand Journal of Ecology, 42(2), 158–168.
Miskelly, C. M., Greene, T. C., McMurtrie, P. G., Morrison, K., Taylor, G. A., Tennyson, A. J. D., & Thomas, B. W. (2021). Species turnover in forest bird communities on Fiordland islands following predator eradications. New Zealand Journal of Ecology, 45(2), 1–15.
Schadewinkel, R. B., Senior, A. M., Wilson, D. J., & Jamieson, I. G. (2014). Effects on South Island robins (Petroica australis) from pest control using aerially applied 1080 poison. New Zealand Journal of Ecology, 315–321.
van Heezik, Y., Ray, S. M., Jamieson, I. G., Allen, O., & Schadewinkel, R. (2020). Impacts of aerial 1080 predator control on nest success and adult survival of South Island robins. New Zealand Journal of Ecology, 44(2), 1–11.
On Thursday 28 April, ZIP field rangers returned to their tent in the Perth River Valley to find that kea had reduced it to shreds. The Perth River Valley is a remote and rugged 12,000 hectare site within the footprint of the Predator Free South Westland project area. ZIP has been working to eliminate possums, rats and stoats from the site since 2018, and the area is now effectively predator-free.
The large tent, located at the confluence of the Perth and Barlow Rivers and affectionately referred to by the team as the ‘Content’, has been a permanent fixture in the Perth River Valley field site since late 2020. While the field team have enjoyed frequent encounters with kea at the Content, this was the first encounter in which kea in this part of the field site had lived up to their reputation for mischief and destruction – and they certainly made up for lost time!
During the weekend of Saturday 30 April, the team returned to remove the damaged tent, and found a mob of eight unbanded juvenile kea on, and around, it. As gear was removed from the tent, the birds amused themselves by climbing over the neatly stacked equipment, undoing packages and opening boxes.
The tent, wooden base and all, was removed from the site and returned to the ZIP field base in Franz Josef, where it will undergo some sorely-needed repairs and maintenance. Fortunately for the team, the tent fly appears to have sustained most of the damage, so with the purchase of a new fly the Content should live to fight another day – perhaps at another location within the Predator Free South Westland project area.
ZIP Chief Executive Al Bramley says, “While certainly inconvenient for our rangers, this encounter is another positive sign that kea in the area are continuing to do very well in the absence of possums, rats and stoats. The team is thrilled to be seeing the results of our work with Predator Free South Westland to protect these charismatic, cheeky birds, and we look forward to seeing what hijinks they get up to next!”
Predator Free South Westland has now completed the second phase of a predator elimination operation in South Ōkārito Forest. This is a major milestone for the project, which seeks to protect and restore nature by eliminating possums, rats and stoats from 100,000 hectares across South Westland. Now, the work to protect the forest against predator re-establishment begins.
Predator Free South Westland Board Chair Katie Milne says, “The elimination of invasive predators from the forest of South Ōkārito will have significant benefits for the last remaining population of New Zealand’s rarest kiwi, the rowi, along with the many other native taonga that call this area home.”
The first phase of the operation was completed in November 2021, and achieved a substantial reduction of possums, rats and stoats. However, a small number of rats survived, and went on to breed in the site. To remove this emerging population, the second phase was initiated on 23 March.
Due to the nature of the South Ōkārito site, this predator elimination operation was particularly complex, and required a combination of aerial broadcast, ‘trickle sowing’, hand- and drone-laying techniques to complete. This complexity was further compounded by a highly unusual turn of events for the West Coast: low rainfall! To ensure that target predators interact with the toxic baits, it is important that no non-toxic prefeed baits remain in the environment when toxin is applied. In South Westland, this would typically occur within 1-2 weeks. In this instance, the prefeed application was followed by 23 fine nights before sufficient rainfall occurred to degrade the bait. Toxic bait was applied between 10-13 April.
The operation appears to have been a success. Pleasingly, no rats have been detected since the operation. If any rats are detected in the coming weeks, they will be removed using targeted ground-based techniques.
A small number of stoats, and an estimated two possums, have been detected in the site since the operation was completed. The team is now working to remove these using targeted ground-based techniques before they are able to re-establish a population.
The measures taken to minimise the risk of karoro (black-backed gulls) eating bait appear to have also been largely successful, and substantially reduced the impact on the karoro population. Pleasingly, there have been no reports of affected dogs or livestock.
The field team has been pleased to report many kea sightings since the operation, and surveys of popular kea sites are also encouraging. A group of kea (including this season’s fledglings) were recently seen at the Pakihi Walk carpark, and local helicopter pilot Gus Gordon reported seeing a flock of kea over the Waiho Loop.
ZIP Operations Director Duncan Kay, who oversees the predator elimination work on the ground, says, “The Predator Free South Westland team has greatly appreciated the ongoing support and patience of the local community during our work to eliminate invasive predators from South Ōkārito. We are now looking forward to protecting the site and watching the native taonga respond!”
In December 2020 we reported that the number of native birds in the Perth River Valley was beginning to recover due to the removal of predators over the previous 20 months. This work is part of the Predator Free South Westland project.
Since then, we have continued to see positive signs of native bird recovery. An insight into their recovery is enabled by the network of 142 lured trail cameras in the Perth River Valley that are deployed to detect possums (Trichosurus vulpecula), ship rats (Rattus rattus) and stoats (Mustela erminea). We retrieve the data from each camera every 4 to 6 weeks, and then plot and analyse it. In the almost 3 years that the cameras have been out we have amassed over 2.5 million images!
Each blue dot shows the location of a trail camera in the Perth River Valley. Each camera is set up in front of lure.
A rat investigates a MotoLure (an automated lure dispenser), March 2021
The predator detection data provides vital information about the number and extent of predators, which helps us to plan how to respond in order to eliminate them. The camera network also regularly detects native birds. These incidental detections also provide a useful indication of how well native species are responding in the absence of predators.
In October 2020 we analysed almost two years’ worth of native bird detections from this network. In January 2022, just over a year later, we once again analysed the proportion of cameras that detected native birds per month, over time.
Please note, the detection network is set up to detect our target species/predators, not native birds. The native birds detected are incidental, and are mainly species that spend time or feed on the ground. Species that naturally occur at low densities, or are primarily arboreal or waterfowl are less likely to encounter one of the cameras.
Incidental detections can provide an indication of the status of native birds in the valley; which for many species, reflects how their populations are responding in the absence of predators. In this update we focus on three species that are regularly detected across the network, from the valley floor to the alpine tops. These species are kea (Nestor notablis), kakaruai/South Island robin (Petroica australis australis), and ngirungiru /South Island tomtit (Petroica macrocephala). The detection rates per month for these species are shown on the following trend graph.
Detections across the Perth River valley trail camera network of kea, kakaruai and ngirungiru from March 2019 - January 2022
We assume that regularly recorded native species detections also reflect their population trends (just as we do for the predator population trends we analyse from trail camera data).
Some common features of the detection data for of the three species are:
The number of detections fluctuate over each year, peaking in summer with new fledglings, and dipping in winter/spring as the birds are nesting
For all three species, detection rates in the month of March have at least doubled between before we undertook predator removal in 2019 and two years later in 2021.
Kea
A kea caught on trail camera, October 2021
The local kea population in the Perth River Valley has benefited from previous predator management programmes and local kea experts estimated there were between 75-100 birds in the Valley before we started working there.
The effects of predation on kea and their nesting success are well researched. We know that when predators are managed with well-timed aerial 1080, more than 70% of kea nests are successful with at least one chick surviving. Without intervention only 40% of nests succeed and this drops to less than 10% of nests when there is a stoat plague (Kemp et al., 2018).
Kea detection rates fluctuate with the seasons, with higher activity in forests (where most of the trail cameras are) over winter, and above the treeline over summer. Despite that, kea detection rates are generally trending upwards.
Detections of kea increased from 8% in March 2019 (i.e. before predator removal began) to 15% in March 2021.
Some of the fluctuation in kea detections could also be due to a bumper breeding season in 2019, after which the fledglings then dispersed to other parts of the backcountry. To put it more technically, there was a “double-clutch” event in 2019 (i.e. kea nested twice, resulting in a higher-than-normal number of chicks), with the result that the local population appeared to increase substantially. That summer (i.e. 2019/20), our field rangers noted seeing fledglings of two different sizes in the Perth River valley. And then, in early 2021, a team monitoring and banding kea noticed a high number of juvenile kea in the adjacent Whataroa-Butler valley. It is possible that this valley may now be home to many of the birds that originally began their lives in the Perth River Valley.
Kakaruai/South Island robin
Kakaruai/South Island robin are sensitive to predation (Schadewinkel et al., 2014). Research has shown the nesting success of these at-risk birds significantly improves in the absence of predators, and we should be able to start seeing a difference 1-3 years after a predator operation (van Heezik et al., 2020).
Detections of robins increased from 5% in March 2019 (before predator removal began) to 11% in March 2021.
A kakaruai in front of a lure, May 2021
Ngirungiru /South Island tomtit
Of the three species we’ve focused on for this update the ngirungiru has had the most dramatic upward trend in detections.
Even taking into account seasonal fluctuations, ngirungiru have had an increase in detections-from 22% of the camera network in March 2019 (before predator removal began) to 55% in March 2021.
A ngirungiru, September 2021
However, over time we actually may see fewer ngirungiru due to competition with other native species. Recent research suggests that as the numbers of kakaruai grow, they may begin to displace the ngirungiru, and we may see a natural reduction in their numbers (Miskelly et al., 2021).
Other Native Birds
Yellow-crowned kākāriki continue to be regularly seen and heard, and are even beginning to feed on the ground in front of some of the cameras.
A kākāriki beside a MotoLure, June 2021, and a pair of kākāriki recorded August 2021
It’s particularly exciting to be seeing and hearing kākāriki, as their presence is often a good natural indicator of the overall health of a forest or ecosystem (McLennan, 2017).
In August 2019, we began sighting kākā in the Perth River Valley. While we have had more regular kākā sightings from the field team over time, camera detections have been sporadic; most likely due to their slow breeding cycle (Powlesland et al., 2009), and apparently low numbers pre-operation.
Kererū (Hemiphaga novaeseelandiae) continue to pop up in camera detections; although this is sporadic as they don’t often forage on the ground. We previously reported seeing flocks of up to 30 kererū in the skies—field team members have now even seen flocks of up to 80 birds!
A kererū on the sunny forest floor by a MotoLure, February 2021
Whio do not often show up on our detection cameras because very few cameras are located alongside waterways, which are the natural habitat of whio. That’s to prevent cameras from being washed away in floods. We have, however, continued to see adults and chicks each year in the Perth River Valley.
We also reported on several other native bird species in December 2020, which the field team continue to see and hear; e.g. korimako/bellbird (Anthornis melanura), tauhou/silvereye (Zosterops lateralis), kārearea /New Zealand falcon (Falco novaeseelandiae), ruru/morepork (Ninox novaeseelandiae), and seemingly endless tūī (Prosthemadera novaeseelandiae).
These incidental and anecdotal detections are a very good indicator that native birds in the Perth River Valley are continuing to recover and that predator freedom has had a positive effect on their populations.
“The bird life on my recent trip into the backcountry was certainly some of the best I have experienced, particularly in the Perth valley from Nolans hut. It’s up there with what I saw on the southern end of Rakiura, and in the Landsborough valley. We spotted a couple of groups of kea, but most noticeable was the kereru; lots and lots of them! Congratulations and keep up the good work.”
Acknowledgements
Thank you to Matt Hickson of the Department of Conservation for a review of an earlier draft of this update.
References
Kemp, J. R., Mosen, C. C., Elliott, G. P., & Hunter, C. M. (2018). Effects of the aerial application of 1080 to control pest mammals on kea reproductive success. New Zealand Journal of Ecology, 42(2), 158–168.
McLennan, J. (2017). The Cape to City Programme: baseline bird counts in treatment and non-treatment areas. A Report Prepared by John A McLennan Environmental Services Ltd, Havelock North, for the Cape to City Governance Group.
Miskelly, C. M., Greene, T. C., McMurtrie, P. G., Morrison, K., Taylor, G. A., Tennyson, A. J. D., & Thomas, B. W. (2021). Species turnover in forest bird communities on Fiordland islands following predator eradications. New Zealand Journal of Ecology, 45(2), 1–15.
Powlesland, R. G., Greene, T. C., Dilks, P. J., Moorhouse, R. J., Moran, L. R., Taylor, G., Jones, A., Wills, D. E., August, C. K., & August, A. C. L. (2009). Breeding biology of the New Zealand kaka (Nestor meridionalis)(Psittacidae, Nestorinae). Notornis, 56, 11–33.
Schadewinkel, R. B., Senior, A. M., Wilson, D. J., & Jamieson, I. G. (2014). Effects on South Island robins (Petroica australis) from pest control using aerially applied 1080 poison. New Zealand Journal of Ecology, 315–321.
van Heezik, Y., Ray, S. M., Jamieson, I. G., Allen, O., & Schadewinkel, R. (2020). Impacts of aerial 1080 predator control on nest success and adult survival of South Island robins. New Zealand Journal of Ecology, 44(2), 1–11.