Collections / Pest management
Possums are the country´s worst animal pest of native forests and the principal carrier of bovine TB, which has an enormous impact on our entire dairy–beef–venison industry. Ferrets also carry bovine TB, and are serious predators of ground–nesting birds e.g., the rare black stilt. However, stoats and rats pose the greatest threat to native forest species, endangering species such as kiwi, kākā, kākāriki (parakeets) and mōhua (yellowhead).
New Zealand is constantly at risk from accidental introductions of new insect pests and weeds. However the biggest weed threats can be found among the many exotic plants already in the country. Established insect pests are seriously affecting native ecosystems (e.g., German and common wasps have a severe impact in beech forests) and we must be constantly vigilant in detecting other new insects pests such as ants.
Possums in dryland ecosystems
Al Glen summarises some interesting aspects of possum research on Molesworth Station
The introduced brushtail possum is a major environmental and agricultural pest in New Zealand. Little information is available on the ecology of possums in drylands, which cover around 19% of the country, yet possums are a pest of conservation concern in these areas. They also carry bovine TB, and the drier areas of the South Island high country contain some of the last reservoirs of TB in New Zealand. In the last five years or so, members of the Wildlife Ecology and Epidemiology Team have been studying the epidemiology of TB in wildlife (including possums) on Molesworth Station, north of Hanmer Springs.
During these studies, largely funded by the Animal Health Board, the team have also gleaned a great deal of information on the ecology of possums in drylands. Al Glen (Lincoln) and colleagues have described the summer diet, feeding preferences, movement patterns and survival rates of possums in this dry, mostly unforested environment. This basic ecological information will be useful in modelling and managing the impacts of possum populations in drylands.
The summer diet, based on the stomach contents of 100 possums, was dominated by forbs (herbaceous flowering plants) and sweet briar, both of which were consumed in larger amounts than expected based on their availability. Possums also strongly preferred crack willow, which was uncommon in the study area and consumed only occasionally, but in large amounts.
Radio-tracking of 14 male and 15 female possums revealed unusually large home ranges. Whereas possums in New Zealand forests or farmland typically occupy home ranges of 1 - 2 ha, possums on Molesworth occupied areas averaging 5.1 ha. The most common daytime refuges of radio-collared possums were sweet briar shrubs, followed by rock outcrops. Estimated annual survival was 85% for adults and 54% for sub-adults.
Differences between the diets, activity areas and den use of possums on Molesworth Station and those in forest or farmland most likely reflect differences in availability and distribution of resources. The results suggest that invasive willow and sweet briar may facilitate the existence of possums by providing abundant food and shelter. In turn, possums may facilitate the spread of weeds by acting as a seed vector.
This work is being followed up with a more intensive study of possum movements and home ranges in dryland environments of inland Marlborough and Central Otago by Ivor Yockney, Graham Nugent, Carlos Rouco and Grant Norbury.
Feral cats on Pitt Island
Feral cats, mice and ‘men’ inhabit Pitt Island, the second largest island (5,700 ha) of the Chathams. Bruce Warburton notes that, without wild cats, more native bird species might also become inhabitants of the island.
The island is also home to other introduced wild vertebrates including Pitt Island sheep (derived from Saxony merino), wild pigs (providing the islanders with their main recreation), and weka (introduced from the NZ mainland), which are eaten by the islanders. Although there has been farming on the island for over a century and fishing boats operating from the island, rats have not managed to establish there. The Department of Conservation are looking at options for managing the feral cats and invited Bruce Warburton (Landcare Research) to visit the island in August to provide advice and discuss the issues around control versus eradication.
Bruce notes “The island has the potential to provide a haven for several threatened species including the Chatham Island pigeon (parea) that became extinct there in the 1970s, the Chatham Island tui (now in low numbers), and the well known black robin that were rediscovered on a small offshore island by Sir Charles Fleming in 1938. By 1980 there were only five individual robins including one breeding pair left, but now there are about 200-250 on several small offshore islands. If cat numbers could be reduced or (ideally) eradicated from Pitt Island, then the robin and many other bird species will have a larger island to occupy. A large range of seabirds including petrels and shearwater will also benefit from having a large island to re-colonise.”
There are about 35 local residents on the island (farmers and fishermen), most if not all having pet cats. Residents are concerned that if feral cat numbers are reduced, there will be an increase in mice. Bruce says this is unlikely, however, because the increases in mouse numbers will be driven by food availability, and, whether cats are present or not, when there are periodic increases in food abundance, mouse numbers will increase.
DOC staff have been working closely with the residents to ensure any planned work has their support and commitment. Part of this has been in getting all domestic cats neutered and an agreement that all new pet cats brought to island will be neutered before arrival.
If eradication is chosen as the preferred option then Bruce says that before commencing, the Department must be certain that they can satisfy the requirements for eradication including: (1) all feral cats can be put at risk (i.e. killed), (2) feral cats can be killed faster than they can breed, (3) immigration or risk of re-introduction is zero, (4) control methods acceptable by locals, and (5) funding must be maintained until the last cat is removed. John Parkes and the Invasive Species International team have many years experience in island eradications including feral cats, and the learnings from this work can be applied to Pitt.
TB and pest management on Molesworth
Ivor Yockney and several wild sentinel pigs were (slightly reluctant) film stars in TVNZ's 'Country Calendar'.
Last autumn, Country Calendar were filming the huge Molesworth cattle muster and wanted some additional footage of the work Landcare Research was doing in partnership with Molesworth Station on TB control. In particular,the Country Calendar staff were very keen to get some footage of the sentinel pig research.
Sentinel pigs are purpose bred TB-free pigs that are released to the wild to go and search out TB. Pigs are great scavengers (as Ivor says "like disease vacuum cleaners"). Therefore pigs can be used to do a job that would be incredibly time consuming for ground staff to do.
Ivor says he was contacted by the Country Calendar crew and asked if he could get a bundle of pigs ready at the Muzzle Station pig breeding pen at short notice and whether he would go and do some radio tracking with the film crew of wild released pigs.
At that time of year, field site can only be accessed by flying in. Not a problem as Ivor explains.
“I have been flying for about six years and hold a Commercial Pilots Licence. Flying into my study sites (which I would have to do anyway) is a very satisfying addition to my job. I can be in Muzzle or Molesworth Stations in about an hour compared to a day’s driving and at less cost than 4WD vehicle mileage! Most of my flying now is mountain flying and landing on farm strips rather than between airports.
“Working in a field site that only has air access only at this time of year is logistically difficult enough without the complication of also trying to work alongside a film crew. When the forecast was looking a bit dodgy, the crew decided to come in a day early. I still had a day’s work left to do but the filming wouldn’t take long … or so I thought.
“A crew of three eventually arrived (late) in two helicopters and quickly set about filming me trying to muster all the wild pigs into a holding yard. Easier said than done when two of the cameramen are standing near the gate you’re trying to muster pigs through. A spot of kind explaining was called for … these little piggies were in fact wild pigs and there was no way they’d go through that gate with any humans nearby. I finally got the crew sorted, the pigs in the holding pen and was able to anesthetise one (of the pigs) in order to fit a GPS radio collar in front of the camera. After a couple of takes and quick interview, the film crew then wished to go radio- tracking and filming some wild pigs by helicopter. They wanted the pigs to walk past the camera set on a tripod somewhere nice and flat and clear of vegetation - yeah right!! Wild pigs remember!!
“However after finding three of my sentinel pigs about 20km up the Clarence River, we were in fact able to muster them out using the helicopter and get them across an open flat right in front of the camera. It’s great when animals co-operate but I suspect the film crew now have a totally unrealistic view of how cooperative wild animals are.
“After a few more takes and a bit of helicopter-to-helicopter filming, we were done. I was flown back to the pig pen (to finish the rest of my day’s work, it was now mid afternoon) while the film crew continued on back to Lake McRae and the rest of the Molesworth muster.”
For more information about sentinel pigs, see “Which TB host is the best TB canary?” in Kararehe Kino.
For more information about our research on Molesworth station, see Discovery.
From Spain to Central Otago
Carlos Rouco Zufiaurre is investigating possum ecology in dryland ecosystems
Since arriving from Spain last January, Carlos has been working with Grant Norbury, James Smith, Roger Pech and Andrea Byrom studying possums in Central Otago to improve knowledge of the ecology of possums in dryland ecosystems such as grass/shrub habitats of Central Otago. Using ‘capture, mark and recapture’ techniques, the researchers have concluded that possums are abundant in this ecosystem, especially in areas of greater shrub cover.
Carlos says “We have also been monitoring the movements of 15 possums with GPS-collars during Spring and Winter of this year, obtaining interesting results about denning behaviour and night activity. We are about to embark on a larger study, funded by the Animal Health Board, to gain a more detailed understanding of habitat use by possums in southern South Island habitats, and to determine where surviving possums (and TB) aggregate after control. Our findings will increase the efficiency and effectiveness of ground control of possums in dryland habitats.
“Alexandra is 19,000 km from my hometown Seville. Spain is almost the antipodes of New Zealand so I couldn’t be any further from home! The actual habitat structure in Central Otago is not too different to what we could find in southern Spain. Unfortunately the winter down here is far from Seville’s average winter temperature of 11.5ºC!
“The presence of wild rabbits in my Otago study site reminds me of doing my PhD. Before coming to New Zealand, I worked for seven years trying to ensure the recovery of rabbit populations for endangered predators in Spain. So imagine how I felt last April when I saw the results of the Easter Bunny Hunt competition in Alexandra … 23,000 rabbits dead in one day! Despite such differences, the environment could not be better for our research and my experience in New Zealand has been very worthwhile.”
Choosing the best methods for controlling possums and other pests
Choosing the best methods to control possums, rats, ferrets, stoats and feral cats has been made easier with the production of a publicly available internet-based Decision Support System or ‘DSS’.
Researchers at Landcare Research developed the application primarily for local authority pest managers, but it is also applicable to anyone needing to control mammal pests.
“Pest control has become quite complex over the last 10 years with new legislation and regulations, new pest control products, increasing public interest in conservation and pest problems, and increasing privatisation of the pest control industry,” researcher Dr Dave Morgan says.
“Local authorities are also under increasing accountability to rate-payers and all of this led to the idea of developing a system that would help people select the most appropriate control methods by a transparent, objective process.”
The DSS was designed by identifying the ‘generic’ questions that arise when pest managers are thinking about what control methods to use. Because the questions require ‘yes/no’ responses, the system is easy to use and unambiguous. The questions are focussed around the key issues of: legislation, operational aims, land tenure, farming practice, public and environmental safety, community views and involvement, and landowner views.
By considering these factors in a logical and systematic way, a number of options are presented. These are further narrowed down by establishing what control methods have been used previously because frequently repeated use of most methods results in declining effectiveness. Finally, recommended options are made on the basis of the likely cost of the remaining suggested methods.
Links are given to ‘best-practice’ advice for all methods. This is based largely on documents produced by the Department of Conservation and by the National Possum Control Agencies. Most of the best-practice advice is based on research carried out in New Zealand.
The system therefore emulates the decision-making process that an experienced, well-informed pest manager would typically follow, Dr Morgan says.
“The DSS is designed to support human decision-making, not replace it. That’s because there is always the possibility that the DSS may not consider every constraint that applies to a particular pest control operation”.
While the DSS guides the selection of appropriate control methods, it is not a complete planning tool for pest control operations. However, links to additional planning tools are given in the ‘help’ sections throughout the DSS.
The system will be updated with new information and Dr Morgan encourages users to send feedback.
The DSS is available at: http://pestdss.landcareresearch.co.nz/
Managing multiple mammalian pest populations
Despite spending approximately $110 million per annum on the management of mammalian pests, they are still here and still threatening biodiversity conservation.
Even where pests are managed, effective control may be seriously constrained by the unpredictable responses of other pest species. For example, rodent numbers sometimes increase following possum control operations, which may lead to increases in stoat populations and a consequent decrease (through predation) of some bird populations.
Wendy Ruscoe (Landcare research) and her colleagues have completed a large-scale, multi-faceted experiment that has been investigating the driving factors in interactions between pest species and how these may affect the outcomes of pest control. Wendy says every man and his dog (literally) have worked on the project, with the key Landcare Research staff being Peter Sweetapple, Ivor Yockney, Roger Carran, Mike Perry and Sam Cave. There were eight 900-ha study sites in mixed podocarp-tawa forests across the Kaimai Ranges, Manukau Plateau, Whirinaki and Te Urewera (the last 2 requiring helicopter access).
The researchers were investigating whether:
- food availability drives temporal variation in pest abundance
- removal of top-level predators results in increases of secondary pests because they are not being eaten
- removal of a pest population leads to increased competitor pest populations.
During the four years' of field work, the team experimentally manipulated pest populations, with each of the ‘treatments’ replicated over the eight study sites, by:
- controlling possums and rats with a one-off aerial 1080 baiting operation,
- using same control protocol for possums and rats but with continuous additional control of rats with toxic bait in bait-stations
- controlling stoats with continuously set traps, and
- no-treatment (no control).
On each site, the baseline population size and temporal changes of rats, mice, stoats and possums were monitored. Rats, mice and possums were live-trapped, marked with ear tags, and released during 5-night trapping sessions in November, February, May and August. Stoat populations were monitored using tracking tunnels and hair-collecting tubes, with the hair being used to identify individual stoats by DNA ‘fingerprinting’.
Additional small-scale experiments quantified how stoats (predators) and possums and rodents (primarily herbivores) modified their food intake rate with varying food availability. Ground-dwelling invertebrates were monitored using pit-fall traps before and after each control operation. Wētā were also counted in purpose-built wētā houses attached to trees.
Carrying out all this fieldwork was a huge logistical exercise and depended on skilled field staff. Mostly everyone camped or used huts for up to two weeks at a time, three sessions a year just for the monitoring. Wendy notes that they also needed a raft of permits … from Landcare Research (animal ethics approval), DOC (research permits and permits to land helicopters in some areas), consent from four iwi groups, permission to use veterinary drugs, cyanide licenses, Medical Officer of Health Approval. “Getting all these approvals was no easy task.” Wendy says they also worked with AHB to have the initial 1080 operation done (part of a job they were doing anyway), and local contractors did the continuous stoat trapping and rat control.
Results
Results of the experimental manipulations produced both expected and unexpected results.
- Removal of the top predator (stoat) from the system did not lead to an increase in the ‘meso-predator’ (rat) as hypothesized.
- However removal of possums using 1080 lead to a significant increase in the ‘competitor rats’ with rat numbers increasing to higher levels than they were prior to 1080 baiting and to higher levels than in the sites that weren’t poisoned at all.
- Similarly, on sites where both possums and rats were controlled to low levels, mouse population numbers increased to higher than they had been previously.
- Where rat populations were reduced, there was an observable increase in occupancy rates of the wētā houses by tree wētā - a favourite rat food.
The data collected from all these experiments is now being used to develop computer models of the four pest species (possums, stoats, rats and mice) and their complex interactions with each other and their environment. These models will be a significant breakthrough in predicting variation in pest abundance over time, and how secondary pests will respond to primary pest control. The models will enable pest managers to assess the relative biodiversity and economic benefits of alternative pest control strategies to protect conservation assets.
Wendy emphasises that “clearly, the benefits of pest control operations must be assessed at the ecosystem level if biodiversity assets are to be protected.”
Feasibility study to save a jewel of biodiversity - the Juan Fernández Archipelago
Al Glen (Landcare Research) reflects on the islands that inspired the Robinson Crusoe stories
The Juan Fernández Archipelago, 700 km west of mainland Chile, is a biodiversity hotspot with myriad rare and endemic species. The importance of these remote oceanic islands has been recognised with their protection as a National Park and as a UNESCO Biosphere Reserve. They have also been short-listed for World Heritage status.
Among the species unique to the islands is the Juan Fernández firecrown, a critically endangered hummingbird that is the only representative of its genus. Over 60% of the native plants are endemic, also including entire genera. Indeed, the Juan Fernández has been called the Galápagos of plant diversity.
The unique natural values of the Juan Fernández are rapidly being eroded by the impacts of invasive species. Weeds such as blackberry and Chilean guava have invaded much of the archipelago, displacing native plants. A host of vertebrate pests - rodents, cats, goats and rabbits to name a few - have wreaked havoc through processes such as herbivory, predation and trampling. The islands are teetering on the brink of invasion meltdown.
In May 2010, a team of scientists travelled to the Juan Fernández to assess the feasibility of eradicating various invasive species from the archipelago. Led by Alan Saunders (Landcare Research / Invasive Species International), the team also included Karl Campbell (Island Conservation), John Sawyer (DOC), Al Glen (Landcare Research), and Consultants Rachel Atkinson and Hernán Torres. The feasibility study was funded by Island Conservation with support from the Ministry for Environment.
The Juan Fernández Archipelago consists of Santa Clara, Alejandro Selkirk and Robinson Crusoe Islands. The latter two owe their names to Alexander Selkirk, the stranded sailor whose 4½-year ordeal inspired Daniel Defoe’s classic novel Robinson Crusoe. Most of our time was spent on Robinson Crusoe, the only inhabited island in the group. The mountainous terrain offers few locations for an airstrip, but the 17-km hike from the airport to the town provided an excellent opportunity to familiarise ourselves with the island and its flora. As we walked, I contemplated the solitary existence of the island’s first human inhabitant, and couldn’t help but wonder if he would still recognise the place today.
Our overwhelming impressions were of the irreplaceable natural values of the Juan Fernández and the gravity of the invasive species problem, but also of the passion and enthusiasm of the local community to preserve their unique islands.
In terms of eradicating invasive species, the Juan Fernández presents some interesting challenges. Because the islands have a wide range of invasive plants and animals, these species are likely to interact with one another in complex ways. Thus, treating species in isolation could have undesired consequences. For example, removal of goats may allow weeds to grow unchecked. Management will therefore require an integrated, multi-species approach.
The archipelago is also home to around 700 people. Globally, there have been few eradications of invasive species from inhabited islands, and none without the full support and dedication of the local community. This adds a complex social dimension to the feasibility study.
Despite the tragedy of a tsunami (February 2010, following the Chilean superquake) that took sixteen lives and devastated the town of San Juan Bautista, the islanders show tremendous resilience. One community leader spoke of the rebuilding phase as a chance to create a greener, more sustainable community. With such vision and courage, there is hope for the future of these remarkable islands.
Weeds & pests threaten biodiversity of the Ogasawara (Bonin) Islands
In late August 2010, Peter Bellingham and Hiroko Kurokawa visited the Ogasawara Islands to look at the invasion of the forests by an introduced tree, akagi (Bischofia javanica). The islands are subtropical (latitude 27 degrees) and are about 1000 km south of Tōkyō, and can only be reached on a 25-hour ferry journey from Tōkyō. They are rugged and remote oceanic islands, never connected to Asia, so all the native plants and animals colonised the islands by dispersal over oceans, and many new species have evolved on them. About 40% of the plants on the Ogasawara Islands are endemic to them. Some of the native plants have close relatives in Japan, but others have their closest relatives on tropical Pacific Islands, and a few in south-east Asia.
People, relative newcomers, have changed the islands
The islands probably had no permanent settlement before the beginning of the 19th century, when they were colonized briefly by American whalers and a workforce of Hawaiians. Japan colonized the islands in the mid-19th century, and began a process of clearing the forests, first for valuable timber. The great Meiji Shrine in central Tōkyō is partly built of the mulberry unique to the islands and now almost completely gone. The islands were then cultivated for sugar cane, and the great colonies of seabirds, especially albatrosses, were exterminated for their feathers.
During the Second World War, the islands were evacuated, and they were occupied by American soldiers until 1968, during which time agricultural land was largely abandoned. After the islands were returned to Japan in 1968, some of the original inhabitants returned and other new settlers arrived.
Only two islands are now inhabited - Chichijima (2000 people) and Hahajima (440 people, and two hours’ ferry sailing south from Chichijima). The islands are politically part of metropolitan Tōkyō, and this ensures infrastructure, including road-building, proceeds apace. Subtropical crops are cultivated for the Japanese market, and tourism (nearly all Japanese) is an important part of the economy (humpback whale-watching in winter, diving around the islands’ reefs and hiking all year round).
Currently the Ogasawara Islands are being considered for UNESCO World Heritage status.
Invasive species threaten the islands’ biodiversity
Not only plant invasions but also invasive animals threaten the islands’ biodiversity values. Goats were introduced to most of the islands as food for castaways. They caused damage to soils and reduced some endemic plants to critically low numbers. Goats have now been eradicated from most of the smaller islands in the archipelago, for example, from remote Nakōdojia (93 ha) in 2003 and Anijima (767 ha) in 2008. However, goats are still present on the larger islands such as Chichijima, where expensive fences have been constructed to reduce their effects.
Ship rats were present on nearly all the islands until recently, and as in New Zealand, their effects on seabird populations have been severe, as they have on seeds and seedlings of some native plants, such as the very rare tall Lobelia boninensis. Rat eradications, using diphacenone toxic baits spread by helicopter, have been conducted on islands.
Eradications of goats and of rats, and control of introduced plants, have been funded by several central government agencies, and also by the Tōkyō metropolitan government.
Further parallels with New Zealand
Peter and Hiroko were taken by staff of the Japan Wildlife Research Center and of the Institute of Boninology to Anijima and tiny Higashijima (28 ha) on which rodent eradications were conducted in early 2010. Peter saw New Zealand-made rodent tracking tunnels employed to detect survivors or new immigrants on Anijima.
Japanese scientists were interested to learn about research carried out by Peter and Susan Wiser (also Landcare Research) on Great Island in the Three Kings Islands in New Zealand, from which goats were eradicated in 1946. A 57-year record of change in Great Island forests, using permanent plots, showed that an expectation of rapid recovery by all species vulnerable to goats had not been realised.
The slow pace of change was dependent on the kinds of birds available to disperse the seeds of many tree species, and also on the ability of plants to compete in the vegetation that goats had favoured, which is some cases had persisted for over 50 years after goats had been eradicated. A key message is that patience may be needed.
As in New Zealand, the land bird fauna of the Ogasawara Islands has been much depleted, and the only surviving endemic land bird species, the Bonin white-eye, survives only on Hahajima (where it is common). The islands’ unique insects on the larger islands are threatened by other invasive animals, especially Anolis lizards accidentally introduced by American troops, and cane toads introduced when sugar was cultivated.
Quarantining the smaller islands against invasions by these species is a priority, and may be hard to achieve as tourism activities such as kayaking could lead to unwitting transport of either of these invaders. Peter says he was impressed at the amount of material in public displays about good biosecurity practice and warning local people and visitors about the effects of invasive plants and animals.
Peter Bellingham works in Landcare Research’s Ecosystem Processes Team, and is based in Lincoln. When he visited the Ogasawara Islands, he was in Japan on a two-month fellowship funded by the Japan Society for the Promotion of Science (JSPS). Hiroko Kurokawa worked as a postdoctoral researcher at Landcare Research from 2006-08. Hiroko’s work in New Zealand focused on whether the functional traits in the leaves and litter of invasive plants (such as their nutrient content and investment in defence chemicals) differ from those of native species, and continuing with similar research in Japan. One of the key purposes of Peter's visit was to develop in-kind approaches to the study of invasive plants in New Zealand and on other islands. This will allow evaluation of whether consistent factors predict the consequences of plant invasions, and whether these effects can be reversed by management.
Managing multiple mammalian pest populations
Wendy Ruscoe (Landcare Research) says that despite spending approximately $110 million per annum on the management of mammalian pests, they are still here and still threatening biodiversity conservation.
Even where pests are managed, effective control may be seriously constrained by the unpredictable responses of other pest species. For example, rodent numbers sometimes increase following possum control operations, which may lead to increases in stoat populations and a consequent decrease (through predation) of some bird populations.
In 2010, Wendy and her colleagues have completed a large-scale, multi-faceted experiment that has been investigating the driving factors in interactions between pest species and how these may affect the outcomes of pest control. Wendy says every man and his dog (literally) have worked on the project, with the key Landcare Research staff being Peter Sweetapple, Ivor Yockney, Roger Carran, Mike Perry and Sam Cave. There were eight 900-ha study sites in mixed podocarp-tawa forests across the Kaimai Ranges, Manukau Plateau, Whirinaki and Te Urewera (the last 2 requiring helicopter access).
The researchers were investigating whether:
food availability drives temporal variation in pest abundance
- removal of top-level predators results in increases of secondary pests because they are not being eaten
- removal of a pest population leads to increased competitor pest populations.
During the four years' of field work, the team experimentally manipulated pest populations, with each of the ‘treatments’ replicated over the eight study sites, by:
- controlling possums and rats with a one-off aerial 1080 baiting operation,
- using same control protocol for possums and rats but with continuous additional control of rats with toxic bait in bait-stations
- controlling stoats with continuously set traps, and
- no-treatment (no control).
On each site, the baseline population size and temporal changes of rats, mice, stoats and possums were monitored. Rats, mice and possums were live-trapped, marked with ear tags, and released during 5-night trapping sessions in November, February, May and August. Stoat populations were monitored using tracking tunnels and hair-collecting tubes, with the hair being used to identify individual stoats by DNA ‘fingerprinting’.
Additional small-scale experiments quantified how stoats (predators) and possums and rodents (primarily herbivores) modified their food intake rate with varying food availability. Ground-dwelling invertebrates were monitored using pit-fall traps before and after each control operation. Wētā were also counted in purpose-built wētā houses attached to trees.
Carrying out all this fieldwork was a huge logistical exercise and depended on skilled field staff. Mostly everyone camped or used huts for up to two weeks at a time, three sessions a year just for the monitoring. Wendy notes that they also needed a raft of permits … from Landcare Research (animal ethics approval), DOC (research permits and permits to land helicopters in some areas), consent from four iwi groups, permission to use veterinary drugs, cyanide licenses, Medical Officer of Health Approval. “Getting all these approvals was no easy task.” Wendy says they also worked with AHB to have the initial 1080 operation done (part of a job they were doing anyway), and local contractors did the continuous stoat trapping and rat control.
Results
Results of the experimental manipulations produced both expected and unexpected results.
- Removal of the top predator (stoat) from the system did not lead to an increase in the ‘meso-predator’ (rat) as hypothesized.
- However removal of possums using 1080 lead to a significant increase in the ‘competitor rats’ with rat numbers increasing to higher levels than they were prior to 1080 baiting and to higher levels than in the sites that weren’t poisoned at all.
- Similarly, on sites where both possums and rats were controlled to low levels, mouse population numbers increased to higher than they had been previously.
- Where rat populations were reduced, there was an observable increase in occupancy rates of the wētā houses by tree wētā - a favourite rat food.
The data collected from all these experiments is now being used to develop computer models of the four pest species (possums, stoats, rats and mice) and their complex interactions with each other and their environment. These models will be a significant breakthrough in predicting variation in pest abundance over time, and how secondary pests will respond to primary pest control. The models will enable pest managers to assess the relative biodiversity and economic benefits of alternative pest control strategies to protect conservation assets.
Wendy emphasises that “clearly, the benefits of pest control operations must be assessed at the ecosystem level if biodiversity assets are to be protected.”
Restoring Lord Howe Island, Australia
John Parkes (Landcare Research / Invasive Species International) says that Lord Howe Island was one of the last places on earth to be colonised by people. It was only discovered by humans in the late 18th century, and only settled in 1834. It is a remote island some 700kms off the east coast of Australia in the Pacific Ocean. It is only 1455 hectares in extent, but has two high mountains, the most southern coral reef and a large number of endemic plants and animals.
With the arrival of humans came invasive plants (230 species of exotic plants have been recorded) and animals. These brought significant threats to the island’s endemic species. Humans, mice, ship rats, feral cats, feral pigs and feral goats together caused the extinction of nine of the 13 endemic terrestrial birds. Remarkably, the cats and pigs were eradicated in the 1980s, and most goats were removed by 2001. Invasive rats and mice, however, continue to threaten native species.
The Lord Howe Island Board has consulted John on several occasions (the use of toxins, to plan goat eradication, and to plan rodent management) as part of their ongoing plans to restore the island’s biodiversity and to protect livelihoods. Most recently, the Board has been considering how to manage the invasive rodents. A particular concern was the cost of a potential eradication attempt in relation to the anticipated economic benefits from reduced rodent depredation on the seeds of endemic Kentia palms - one of the islanders’ main sources of income.
John and his colleagues looked at the usual rules and constraints around the feasibility of eradicating rodents. They also developed a simple cost-benefit model for the palm seed industry - the estimated costs of doing nothing; applying several levels of sustained control; or of attempting to eradicate ship rats only, or both ship rats and mice. Basically, eradication of just the rats gave marginally the best cost-benefit outcome, although eradication of both rats and mice would produce optimal benefits to non-market biodiversity values.
The Lord Howe Island Board accepted the desirability of targeting both rodent species and has appointed a project manager to plan the details of the eradication attempt – widespread sowing of toxic baits over an island partially inhabited by people is not a trivial task! The project has recently received Australia Government funding to progress planning the eradication.
Managing invasive species is a means to an end and not an end in itself. Therefore, while many island projects are focused on a particular pest species - or group of species - programmes are increasingly being initiated that consist of a sequence of ‘pest projects’, where the whole island is treated as the management unit, with restoration as the ultimate goal. Ecologists and economists
are increasingly realising that improved effectiveness and efficiencies can be anticipated from such holistic approaches to island management.
Animal monitoring trip in Whanganui National Park
Roger Carran (Landcare Research) with a story of a 16-day field trip that got a lot more challenging than expected.
The aim of this trip was to establish lines of chew cards and tracking tunnels in several areas within the park to gauge animal abundance prior to an upcoming ‘low sow’ 1080 drop covering about 32,000 hectares of Whanganui National Park.
The trip was planned and organised by Landcare Research (in collaboration with DOC Whanganui) as part of the on reducing the amount of toxin being applied to the landscape whilst maintaining the effective kill rate of possums and rats.
The field team for this trip consisted of a real mix of Landcare Research staff, contracting staff, a couple of guys from Vector Control on the West Coast, and DOC staff based in Pipiriki. All in all we had an awesome crew of strong, competent and experienced bushmen.
Our first study sites were located in the middle of the park up the Whanganui River, so we based ourselves at John Coull Hut, approximately a one-hour up-river via jet boat from the DOC base at Pipiriki. Just before we arrived, there had been torrential rain (which lasted for the first couple of days of the trip) so the river was well up —we had an exciting trip upstream. Whole trees and bloated dead animals floated past. We got up to the hut without hiccup and tied the boat up to the trees sticking out of the water.
The work plan was for each person to be dropped off by jet boat at various points along the river in the morning. Then they were to navigate their way to a specific start point and establish three ‘chew card’ transect lines each before returning to a point on the river where the boat could pick them up. Accessing the park from the river is always a challenge. In many (if not most) places, the river cuts its way through steep sided gorges of soft and slippery Papa clay, making climbing out of the river almost impossible. So, finding appropriate access points was important, and of course these changed with the changing water levels as well.
Everything was running smoothly on the first morning. Everyone managed to negotiate the access points from the jet boat and the rain was easing up. In fact, we all had the work done in record time. It looked like it was going to be a trouble free day ... 'till we found out that one of our contractors had managed to cut his left index finger 90% of the way off with a Svord machete, very nice, very sharp.
From an H&S scenario, things worked in text book fashion. Everyone was carrying radios specifically programmed to the DOC frequencies, spare batteries, EPLOBs (emergency locator beacons), personal tracking devices, GPS’s, maps, compass, and in this case more importantly — first aid equipment. Uncannily, the contractor had just completed a first aid refresher course three days beforehand, and he managed to tape his fingers together and call for help. The DOC jet boat driver came and got him within a matter of minutes, having already called Emergency Services and DOC base to get a helicopter on its way. He was flown out to Hamilton Hospital and had surgery that afternoon to reattach the finger. Everyone did all the right things and the doctors reckon he’ll get 100% use of his hand and finger back, which really is amazing!
So there, we were one team member down. DOC and Landcare Research had in the meantime already organised for another contractor from the West Coast to join us for the remainder of the trip and was there the next day, this time without a machete. The weather fined up and the chew cards lines went out without any more incidents.
The forest and landscape surrounding the Whanganui River is steep and thick. However, the ridges are open and very easy to travel due to the high numbers of goats. Any form of understory has been long since munched by goats; you often come across small groups as you walk through the bush. Introduced over 200 years ago and reproducing at a rate of two sets of twins a year, they’ve stripped the vegetation with gusto.
After putting out all the chew card lines along the river, we split the team into two groups and moved to separate locations. One group headed back into the park near Ruatiti accessing the lines via quad bike, and the other group moved around to Whakahoro. Here we had a lot of interaction with different interest groups using the park; hunters, kayakers, horse trekkers and farmers. It’s always interesting to gauge people’s opinions on conservation and surrounding issues. Once we’d established all the lines, we headed back to Pipiriki to repeat the whole process all over again, bringing in and replacing all the ‘chews cards’ that had been out for a week to see what animals had been chewing them and get a score for the relative animal abundance in the study area.
Return trip to Whanganui National Park
Grant Morriss (Landcare Research) picks up the story.
Aerial 1080 baiting was completed in November 2009 and the monitoring crew were back in to check the results the next month. Roger Carran was unable to come on the trip but Grant Morriss led a crew of 5 experienced contractors assisted by local DOC staff. Unlike the first trip there were no severed appendages and things went remarkably smoothly. Many dead possums were observed while servicing the chew card lines, and the native birds heard and seen alive after the poisoning included robin, tomtit, whitehead, tūī, falcon, grey warbler, bellbird, and fantail. Bats were observed on twilight at the John Coull hut and a kiwi was also heard.
Chew cards were put out on the same lines used for the pre-poisoning and left for 7 nights before being collected and read. It was soon apparent there had been good reductions in rodent and possum interference on the chew cards. A 97% reduction in possum activity was recorded in areas where only 250g/ha of 1080 bait had been cluster-sown, which was better than the reductions measured in the standard sown blocks where 2kg/ha 1080 bait had been used. Reductions in rat activity were high as well with 98-100% reductions in the cluster and broadcast-sown blocks.
These results have contributed to formulating ongoing research into reducing sowing rates with aerial 1080 baiting with very good possum and rat reductions achieved in 2010 with cluster-sown rates as low as 167g/ha. Further operations are planned in 2011 with many thousands of hectares treated with lower sowing rates than is currently the standard.
Footnote: The contractor who almost cut his finger off on the first trip had a few months off work but now has full use of that finger. He has been back doing field work by Landcare Research since the incident.
Future freedom from bovine TB
Graham Nugent (Landcare Research) says it is amazing there are now less than 80 TB infected deer and cattle herds in New Zealand compared to over 1,700 in 1994. Bovine TB is a bacterial disease that affects not only cattle but humans and many other species, including possums. Because Tb was so widespread in possums in 1994, few people considered it possible to eradicate the disease from New Zealand.
By 2008, however, New Zealand has made huge progress in reducing the levels of bovine tuberculosis (TB) in farmed livestock. That prompted the Animal Health Board (AHB) to propose a new national pest management strategy for TB (NPMS) that aims for local and regional eradication of TB from both livestock and possums (the main wildlife host) by 2026. This goal is endorsed by farmers and industry and local who want to protect our reputation as a supplier of safe, high quality meat and dairy products. In late 2010, the proposal for the new NPMS was accepted by the government.
Landcare Research’s work for the AHB contributed substantially to the success of the previous current NPMS, which is on track to achieve fewer than two in a thousand herds (0.2%) infected by 2013. The emphasis now is on local eradication of TB from wildlife – decreasing the cost of reducing possums to very low density while also reducing the amount of poison used, developing alternative methods for breaking the TB cycle, and developing new tools for quickly showing TB has been eradicated locally, so that possum control can be stopped.
Significant projects are being conducted in two remote high country stations, the last areas in northern Canterbury where TB levels in cattle and wildlife had been high. A large-scale aerial poisoning operation in 2008 piloted two new approaches – targeting high-possum-density areas predicted to have the highest risk of TB-infected animals, and a new low-cost, low-toxin approach to 1080 poisoning. This trial completed the implementation of possum control over the most critical parts of the infected area. By 2010 (and for the first time in a more than two decades) the number of TB suspected found by skin testing live animals had dropped to almost zero. In addition pigs, which are highly susceptible to infection when TB-infected possums are present, have been deliberately released in the area as sentinels for detecting TB. Few of the sentinel pigs inside the managed areas have become infected, compared with most of those in an unmanaged area. There is still some infection in both cattle and pigs, but the hope is that the rapid downward trend in the level of infection will continue.
An additional management approach, which is being developed in collaboration with AgResearch and Otago Innovation, a vaccine (BCG) used to protect humans from TB is also showing promise in protecting free-ranging cattle form the natural sources of TB in this area. Partway through the trial, only one (0.6%) of 160 vaccinated cattle have had visible TB infection when slaughtered compare to 10 (5.2%) of 193 vaccinated cattle. Vaccination of cattle may therefore be useful as an interim tool for reducing TB in livestock in areas where it is impractical to undertake effective control of possums.
A new approach to biodiversity protection: local scale to landscape scale
All over New Zealand, there is a huge groundswell of interest in pest control for biodiversity protection. Small, isolated patches may not provide enough habitat to allow native species to survive in perpetuity, but a coordinated approach across tenures could develop ‘metapopulations’ at a landscape scale. (A metapopulation is a group of spatially separated but interacting populations of the same species). Hence local community groups, DOC, regional councils, large and small businesses and research providers all have a role to play.
Recently Wendy Ruscoe, Al Glen (both Landcare Research at Lincoln) and their colleagues began work with the Robertson Foundation Aotearoa, Hawkes Bay Regional Council, and Department of Conservation to set up the Wide-Scale Predator Control Project. This aims to apply ‘metapopulation’ management over a scale of tens of thousands of hectares in the Maungaharuru-Tutira Area. The project considerably expands on DOC’s initiatives in the Boundary Stream Mainland Island (BSMI), which has had pest control for 15 years. Bellbird Bush and Opouahi Reserve nearby, as well as many smaller privately-owned blocks in Hawkes Bay also provide protected native habitat but are separated from BSMI by unprotected agricultural land.
Populations of native species including kiwi, kokako, North Island robin, and Hawkes Bay tree weta persist in BSMI but are constantly under threat of predation by invading pest animals. The threat of predation is especially intense when native animals attempt to move between these protected areas. Wendy and colleagues will determine whether the level of predator control implemented across the pastoral landscape is sufficient for a suite of native species (birds, reptiles and insects) to make more effective use of the network of native forest remnants. They also plan to determine if fragments close to BSMI show a more rapid response than isolated fragments. Models of connectivity between patches will help managers and community groups decide where and when to carry out landscape-scale pest control within limited budgets.