Predator Free 2050 PRACTICAL GUIDE TO TRAPPING possums - rats - Department of ...
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Second edition June 2021 Predator Free 2050 PRACTICAL GUIDE TO TRAPPING mustelids rats possums
Aotearoa New Zealand’s unique and ancient native species of plants and animals will be safe from extinction and flourishing once more, if our lands are free of predators. Predator Free 2050 (PF2050) is a coordinated nationwide goal to eradicate mustelids (stoats, ferrets and weasels), rats and possums from mainland New Zealand by 2050. Predator Free 2050 builds on the achievements of hundreds of scientists, ecologists, iwi and community conservationists and is inspiring thousands more to join the movement. It offers the unifying vision of an endgame, and an action plan to win it. That culture of care and responsibility to nurture the welfare of the land and, by extension, the people, is called kaitiakitanga. Whakahokia mai ngā reo karanga o te ngāngara, o te mokomoko, o te pekapeka, o te manu ki te ngāhere, ara ki te wao nui a Tānemāhuta, pamu, me ngā tāone. Return the voices of the insects, reptiles, bats and birds back to the forests, farmland, towns and cities. Cover image: 2021 NMIT Kaitiaki Whenua Right: Miromiro/tomtit Trap Training. Image: Michelle Bridge (DOC) Image: Shellie Evans
Tohu
Aotearoa has the ambitious goal to be a Use the tohu to show your connection to 1. Foreword........................................................................................................................................................ 1
predator-free nation. We will rebalance our the national PF2050 movement and the
natural environment so our native species mahi (work) you are doing to reach the 2. Our vulnerable native taonga – wildlife........................................................................................ 2
thrive alongside us. predator-free goal.
To succeed, we must come together and Our native species are a part of our natural 3. Staying safe.................................................................................................................................................. 3
support the cause however we can. The tuia whakapapa. They are our family, our
te taiao tohu (symbol) reminds us why we equals, our ancestors. We have a binding 4. Know your target predator.................................................................................................................. 4
are working towards a Predator Free 2050. responsibility to them – just as we do to
It shows our support for the journey through our own whānau. When our native species 5. Monitoring before trapping .............................................................................................................. 19
to 2050 and connects us all to this kaupapa. flourish alongside us, our bonds will be
It is for all Aotearoa. strengthened. People young and old will feel 6. Select the right trap............................................................................................................................. 32
a sense of wonder and connection.
To succeed, we need to unite. 7. Select the right bait or lure............................................................................................................... 42
We all have a role to play.
People. Nature. Together we flourish. 8. DOC best-practice trapping .......................................................................................................... 43
Tuia te taiao.
9. Every trap counts.................................................................................................................................. 58
www.tuiatetaiao.nz
10. Recording trap catch.......................................................................................................................... 60
11. Instructions for DOC-series trap maintenance................................................................... 61
12. NZQA training – NMIT Predator Trapping Methods Course......................................... 70
13. Suppliers of traps, baits, lures and monitoring equipment.......................................... 71
14. Online resources.................................................................................................................................... 72
15. Notes ............................................................................................................................................................ 73
Predator Free 2050 – A practical guide to trapping 2. Our vulnerable native taonga
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– wildlife
1. Foreword 2. Our vulnerable native taonga – wildlife
The 'Predator Free 2050 Practical Guide to The guide also covers the importance of Before the arrival of humans, the only Our native wildlife need three things: safety
Trapping' was developed by the Department pre- and post-predator control monitoring. native land mammals in New Zealand were from predators, suitable habitat and enough
of Conservation (DOC) to support your It describes how to monitor outcomes three species of bats; New Zealand was genetic diversity for long-term resilience.
valuable mahi (work) in protecting Aotearoa (species you want to protect) and results primarily a land of birds, small lizards and Of these, the first – safety from predators –
New Zealand’s unique and highly vulnerable (species you want to control or remove). invertebrates. Our native species evolved needs addressing most urgently.
native taonga species. without mammalian predators, making
For any further information on trapping or These guidelines focus on trapping
them especially vulnerable when these
Your predator control mahi is an extremely the contents of this guide, please contact mustelids (stoats, weasels and ferrets),
animals arrived.
important contribution toward the country’s your local DOC Office or visit the Predator rats and possums – the most voracious
vision of a flourishing natural heritage Free 2050 online toolkit: www.doc.govt.nz/ Due to our country’s unique natural history, predators of New Zealand’s wildlife.
arising from a Predator Free New Zealand – predator-free-2050 our extinction rates are among the highest in
thank you! the world. This is largely due to the impact
Happy trapping!
of introduced predators, invasive species
This concise guide gives you access to
From the PF2050 Communities Team, and loss of habitat.
DOC’s best-practice trapping techniques for
mustelids (stoats, ferrets and weasels), rats Department of Conservation
and possums, including technical advice on
a range of trapping subjects, in an easy-to-
use booklet.
The guide includes all the information
you will need to start your own trapping
programme, no matter how big or small.
You will learn to identify your target
predator, how its natural behaviour is likely
to affect your trapping, which traps and bait
to use, and where and how to place your
trap network.
Female kea feeding its chick in Fiordland. Image: James Reardon ©
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Predator Free 2050 – A practical guide to trapping 4. Know yourXxxxxxxxxxxxx
target predator
3. Staying safe 4. Know your target predator
If you’re a volunteer, you must take reasonable care of your own safety and take care
not to do anything that could harm another person – www.worksafe.govt.nz
Mustelids – stoat (Mustela erminea), ferret (Mustela
furo) and weasel (Mustela nivalis)
Most community groups will have a health
and safety plan in place. You should be This section deals with the three most damaging predators. Predator Free 2050 aims
familiar with this plan and refer to it often. to eradicate mustelids, rats and possums from New Zealand. For information on other
A safety talk at the start of volunteer predators, visit www.doc.govt.nz
activities will ensure the correct personal
protective equipment is being used, identify
any new risks on the day, and inform any
changes that need to be considered to
reduce those risks prior to undertaking the
work. For example, the risks of disease from
handling carcasses and injury from traps are
unique to trapping and should be addressed
in your health and safety plan.
Measures taken to reduce risk of harm or
injury include advising volunteers to wear
gloves or use hand sanitiser, and to use
safety clips when clearing traps.
For further information on your
responsibilities as a volunteer, search for
‘volunteer’ on the WorkSafe New Zealand
Volunteer trappers. Image: New Plymouth Boys website: www.worksafe.govt.nz
High School
For advice on outdoor health and safety, and
planning a trip to remote trapping locations,
Working in the outdoors, and in different
visit www.mountainsafety.org.nz
environments, presents a range of
hazards and conditions that will require
a comprehensive health and safety plan.
Changing weather conditions, difficult Weasel (back), stoat (middle), ferret (front). Image: Alaine Holdom (DOC)
terrain, and working close to coastlines and
waterways will present new challenges for
Mustelids (Mustelidae) are a diverse group All three mustelid species are established
many volunteers. Risk assessment and risk
of small- to medium-sized carnivores. In the in the North and South Islands, and stoats
management strategies (including training)
1880s, three species were introduced into have also reached some of the nearer
need to be applied to all potential hazards.
New Zealand to control the burgeoning offshore islands unassisted. All three
In your role as a volunteer trapper you will rabbit population – stoat, ferret and weasel. species are absent from Great Barrier Island
be required to recognise these hazards and Safety meeting. Image: Kaitake Ranges All have a characteristically long body, short (Aotea), Stewart Island/Rakiura and the
manage the risks they present. Conservation Trust legs and sharp, pointed faces. Chatham Islands.
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Predator Free 2050 – A practical guide to trapping 4. Know your target predator
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| Stoats
Table 1. Mustelid fact comparisons1
Stoats (Mustela erminea)
Stoat Ferret Weasel
Average male
324 g 1200 g 126 g
weight
Average female
207 g 600 g 57 g
weight
Average life span < 1 year (max 3–8) < 1 year (max 5–10) < 1 year (max 2–3)
Usually September
September to
Breeding season to October but can September to March Stoat. Image: Tim Sjoberg (DOC)
November
last longer
Stoats are ferocious predators and the number-one killer of many of New Zealand's
endangered native species.
Usual number of
1 1 (max 2) 1–2 (max 3)
litters per year
Identification Stoats are more common than ferrets and
Stoats have long, thin bodies and sleek, weasels in forest habitats.
Usual litter size 8–10 (max 20) 4–8 (max 12) 3–6 (max 11) pointed heads. Stoats do not make their own dens but
They are smaller than ferrets. Male stoats take over those of other animals. Den sites
grow up to 30 cm long and females up are well hidden and include holes and
Most often cavities in tree trunks and amongst roots,
December to to 25 cm.
rabbit burrows, ditches and piles of logs.
Juvenile dispersal January but February to March January to March Their ears are short and rounded.
sometimes can start Stoats can tolerate extremely wet weather
Their face, upper body and legs are
in November (eg > 6000 mm rain p.a. in Westland and
brown while their chin and lower body
Fiordland) and moderately dry conditions
are creamy-white. Some stoats may be
(eg < 500 mm rain p.a. in parts of Otago
white or pied in winter, particularly at high
Known dispersal and Canterbury).
Up to 65 km Up to 45 km None published elevation in the South Island.
distances
Their tails are relatively long and have Behaviour
bushy, black tips. Stoats are agile climbers, semi-arboreal
Males 1–192 ha (can live in trees) and hunt at any time, day
Males 147 ha Males 200 ha
Females < 1–29 ha Habitat
Average home (16–313) (80–760) or night.
(Not averages, Stoats will live in any habitat where they
ranges (min–max) Females 79 ha Females 122 ha Adult stoats live in separate home ranges
but min–max from can find prey. They can be found in rural
(9–127) (45–230) for most of the year. These often overlap,
overseas studies) communities where they will prey on
particularly between sexes. The size,
domestic fowl, along coastal areas and
length of tenure and pattern of use of
Details in this table and elsewhere in this section on mustelids were obtained from ‘Pest mustelids: monitoring beaches, in remote high country and at
1
home ranges depend largely on the
and control’ (National Pest Control Agencies 2018, available from www.bionet.nz/library) and ‘The handbook of any altitude up to and beyond the treeline,
New Zealand mammals’ (King, C.M. (Ed.) 2005, Oxford University Press). distribution of prey.
in any kind of forest.
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| Stoats
Female stoats move about less during
the breeding season (from September to Predator plague cycle
November) and those with small young
are likely to stay close to dens unless
moving to new den sites.
Breeding females and any juvenile
females in dens will be impregnated
by adult males. Female juveniles are
usually pregnant before they become SUMMER
Predator
independent. Average annual litter size is When forest trees
8–10 (max 20). flower heavily, a lot of
plague
seed is produced
Females caught between November
and August inclusive are almost always
(> 99%) in the pre-implantation phase
of pregnancy. This means they carry
cycle AUTUMN
anywhere up to 8–10 fertilised eggs ready
When seed is abundant,
for implantation in the uterus. the rodent population
increases rapidly
Stoats communicate through scent Northland brown kiwi. Image: Tui De Roy (DOC)
marking, which is thought to convey
information on social and reproductive North Island brown kiwi chicks hatched
status and, possibly, individual identity, annually before they are able to reach a
allowing subordinate animals to avoid stoat-proof weight of > 1000 g.
conflict with larger individuals.
They have a significant effect on coastal
Stoats are prolific breeders. Young males bird species such as wrybills, New Zealand WINTER
mature when they are 10 months old. dotterels and black-fronted terns. Forest Stoats feed on
Males search for females actively during birds that nest in holes in tree trunks
abundant rodents
the breeding season but do not establish (such as mohua, kākā and kākāriki) are
even temporary bonds with them and take particularly vulnerable to stoats, which
no part in rearing the young. can destroy eggs, chicks and incubating
Stoats can reach islands by swimming adults in one attack. SUMMER ONWARDS SPRING
across water gaps of up to 1.5 km and Stoats are implicated in the extinction of
Stoat numbers explode When the seed rots
and they also turn or germinates, plagues
possibly further. A stoat may be able to a South Island subspecies of bush wren, to birds for food of starving rats turn to
reach land at a greater distance than it the laughing owl and New Zealand thrush.
bird eggs and nestlings
can swim by ‘rafting’ on floating material
Stoats, rats and mice form a complex
(such as driftwood logs).
predator-prey relationship in association
Threat with beech tree seed production. In
periodic ‘mast events’ – when high Predator plague cycle diagram: DOC
The serious effect of stoat predation on
levels of beech seed are produced – rat
the survival of many of New Zealand’s bird
numbers explode. As their main prey
species cannot be overestimated. They
becomes more abundant, stoat numbers
are voracious and relentless hunters.
also increase. Later, when the seed
Stoats are a serious threat to kiwi chick supplies run out and rat numbers drop,
survival rates. In areas where they are not the hungry stoats turn their attention to
controlled, stoats can kill up to 95% of birds, insects, bats and landsnails.
7 8
Predator Free 2050 – A practical guide to trapping 4. Know your target predator | Ferrets
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In the 1980s, at least 17 ferret farms were Threat
Ferrets (Mustela furo) established in Northland. When these
Ferrets are a significant pest of both
closed due to a downturn in the market,
conservation and economic importance
many ferrets escaped or were set free,
in New Zealand. They prey on indigenous
which likely contributed to the northward
wildlife and also carry bovine
expansion of ferrets into some of New
tuberculosis (Tb).
Zealand’s remaining prime kiwi habitat.
Ferrets are a serious threat to adult
Behaviour kiwi. They dramatically reduce kiwi
life expectancy from 30+ years to only
Ferrets are mainly nocturnal. Unlike stoats
12 years. In some North Island brown
and weasels, ferrets are not good climbers.
kiwi populations ferrets have caused
Individual ferrets will usually exclude sudden population decline by killing large
others of the same sex from their central numbers of the resident adult birds.
home range. They use their scent glands
Ferrets are known to prey on royal
extensively to leave territorial scent markers.
albatross chicks, yellow-eyed penguins
Ferrets usually mate in September. The and little blue penguins, weka, North
litter, usually of 4–8 (up to 12), is born in Island brown kiwi and numerous
October or November, with young freshwater wetland birds (eg ducks).
becoming independent by late January.
They are considered to be one of the
Females can have a second litter after this
major causes of decline of the white-
if food is abundant. There is high mortality
flippered penguin, and along with cats
in the first year, and an average lifespan in
have contributed significantly to a decline
the wild may be 4–5 years.
in the distribution of grand and Otago
Ferrets will often revisit the site of a kill. skink populations.
The main foods of ferrets are rabbits and
Ferret. Image: Michelle Bridge (DOC) hares. Densities of ferrets seem to be
strongly correlated with density of
Although rabbits are the main diet of ferrets, this mustelid will attack, kill and eat rabbits. A sudden reduction in rabbit
native species. numbers results in hungry ferrets
attacking other animals (such as
Identification Habitat threatened native species).
Ferrets are the largest of the mustelid Ferrets are not as widespread as stoats.
species in Aotearoa New Zealand. Male It was originally thought that ferrets were
ferrets grow up to 44 cm long and females limited to open country like pasture,
up to 37 cm. scrubland and coastal areas, and on
Ferrets have creamy-yellow undercoats the fringes of forests; however, recent
and longer dark guard hairs which give research has found them within some
them an overall dark appearance. Northland forests, where their presence
Legs and tail appear darker than the rest would add to the pressure on already
of the body. threatened kiwi populations.
Face is lighter in colour than the body, Ferrets are generally absent or in low
with a dark mask around the eyes and numbers in places where rainfall is high,
across the nose. where there are few rabbits, or deep
within forested areas.
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Predator Free 2050 – A practical guide to trapping 4. Know your target predator
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| Weasels
Behaviour Threat
Weasels (Mustela nivalis) Weasels can be active during the day and Weasels, being smaller, less common,
the night. more patchily distributed and present
Their breeding season is from September at much lower densities than the other
through to March and a female can have mustelids in New Zealand, are thought
up to three litters during that time. Litter to pose a less significant conservation
sizes average 4.5 kits. risk. However, they are known to have
adverse impacts on lizard, invertebrate
When food is abundant, female weasels
and bird populations.
can breed in their birth year.
In particular, weasels may damage
While mice are their preferred food,
small and localised populations of
weasels are also known to eat birds,
endangered species such as Whitaker’s
mice, geckos, skinks and invertebrates
skink. On the mainland, predation
(including wētā).
pressure and loss of habitat has reduced
Whitaker’s skink to a single remnant
population that remains under constant
threat from weasels, rats and mice.
While weasels are not able to tackle the
larger bird species (eg adult takahē and
kiwi) that are preyed upon by stoats and
ferrets, they will tackle prey much larger
than themselves, so many nesting birds
are easy targets.
Weasel with egg. Image: DOC
Weasels are found in low numbers in most habitats in New Zealand. They pose a significant
threat to native wildlife.
Identification Habitat
Weasels are the smallest and least Weasels are found in low numbers in
common mustelid in New Zealand. Males most habitat types in the North and South
grow to about 20 cm long. Islands but are not present on Stewart
Weasels are brown on their upper bodies Island or on offshore islands.
and white below, similar to stoats. In New Zealand, weasels are less
Their tails are short, brown and tapering. common than stoats and ferrets and may
be displaced by stoats.
To identify a weasel from a stoat, a weasel
does not have a bushy black tip at the end Weasels have been observed in forests,
of the tail and a stoat does. tussock grasslands and farmland. They
are more common in rough grassland
than stoats, possibly because of the
abundance of mice, their preferred prey,
in grassland. Three weasels on the boardwalk at Pauatahunui Inlet, Porirua. Image: Brent Higham
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| Rats
Table 2. Identification of New Zealand rats1
Rats – ship rat (Rattus rattus), Norway rat
Ship rat Norway rat Kiore
(Rattus norvegicus) and kiore (Rattus exulans) Rattus rattus Rattus norvegicus Rattus exulans
Normal adult
Three species of rats have been introduced to New Zealand: the ship rat (sometimes referred Up to 215 g Up to 450 g Up to 187 g
weight
to as black rat or roof rat), Norway rat (often called brown rat, water rat or sewer rat) and kiore
(also referred to as Pacific rat, Māori rat or native rat, even though they are not native to Max. body
230 mm 275 mm 185 mm2
New Zealand). It is thought that kiore arrived with the first Polynesian settlers, about length (HBL)
1250–1300. Ship rats and Norway rats arrived with the first Europeans and spread quickly. Clearly shorter than Slightly shorter or
Much longer than HBL.
Tail length HBL. Thick with pale longer than HBL. Thin
Uniformly coloured.
Home range underside. and uniformly dark.
Noway rat: 0.8–21 ha 19.0–26.0 mm, 14.0–22.0 mm, do 15.5–20.5 mm, cover
Ship rat: 0.3–11.4 ha cover eyes when pulled not cover eyes when eyes when pulled
Ears forward. Fine hairs do pulled forward. Obvious forward. Fine hairs
Kiore: Data unknown not extend beyond hairs extend beyond do not extend beyond
edge of ear. edge of ear. edge of ear.
Identification
Adult hind
28.0–38.0 mm 30.0–41.5 mm 24.5–31.0 mm
foot
Colour of Outer edge dark near
Uniform colouring over
upper side of Always completely pale. ankle, rest of foot and
whole foot, usually dark.
hind foot toes pale.
Fur on back Brown or black3 Brown Brown
Uniform monotone
White-tipped grey White-tipped grey
Fur on belly of grey, white or
giving irregular colour. giving irregular colour.
creamy-white
Length of
6.8–13.8 mm 13.4–19.1 mm 6.4–9.0 mm
droppings
Comparison of Rattus. Image: C. Mahoney Number of
10–12, usually 10 12 8
nipples
Burrows extensively;
Very agile and frequent Agile climber; digs small
climbs much less
climber; rarely burrows; holes; nests on ground;
frequently than
Habits nests mainly in trees or in trees; feeds on
other rats; nests
and shrubs; infrequent ground and in trees;
underground; very
swimmer. infrequent swimmer.
wary; strong swimmer.
Two ship rats preying on a thrush nest.
Image: Ngā Manu Images © 1
Table is from ‘Guide to the identification and collection of New Zealand rodents’ www.doc.govt.nz/documents/
science-and-technical/rodent-identification.pdf
2
The normal maximum weight and head-body length are given for each species. However, larger kiore may
be encountered.
The three colour morphs of ship rat found in
New Zealand. Image: John Innes, Landcare Research 3
There are three colour forms or morphs (not subspecies) of Rattus rattus:
(a) ‘rattus’ – uniformly black back (sometimes has a blueish look); uniformly grey belly
(b) ‘alexandrinus’ – brown back with long black guard hairs; uniformly grey belly
(c) ‘frugivorous’ – brown back with long black guard hairs; uniformly white or creamy-white belly.
13 14Predator Free 2050 – A practical guide to trapping 4. Know your target predator
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| Possums
Habitat Rats have a built-in defence mechanism
Ship rats are found in most habitats which makes them wary of new things in Brushtail possum (Trichosurus vulpecula)
and are now the most abundant and their environment. Therefore, new traps,
bait stations or tracking tunnels need to The brushtail possum was first introduced to New Zealand from Australia in 1837 to establish
widespread rats on mainland New
be installed a minimum of 3 weeks before a fur trade. This release was unsuccessful and a second release 20 years later at the same
Zealand. They are good climbers and are
you need to use them. Southland location was required before they were able to establish.
therefore the rats most commonly found
in forests. Rats have a high rate of population
Norway rats are more typically associated increase. Annually they can have
with human activity and are usually found several litters and produce 11–16 pups.
in urban areas, wet habitats and on some This means control projects must either
offshore islands. control continuously or time their efforts
Kiore were once found all around New carefully to provide protection to native
Zealand and on many offshore islands. On species at vulnerable times (eg for birds
the mainland they are confined to parts of during their breeding season).
Fiordland, Southland and South Westland. Rat food preferences are often passed
They have some cultural significance on socially. This means rats ‘teach’
because of their association with the others about food sources and this can
migration of Polynesians throughout the include their preferences towards poison
Pacific and their value to Māori. and baits.
Behaviour Threat
Rats have a major impact in New Zealand
because they are omnivores – eating
birds, seeds, snails, lizards, fruit, insects,
eggs, chicks, larvae and flowers. The
varied diet of rats also makes them
Brushtail possum. Image: Alan Cressler
competitors with native wildlife for
food sources.
Home range Their tails are capable of grasping
Ship rats are widespread in lowland (prehensile) and help maintain grip until all
Male 0.7–3.4 ha
podocarp-broadleaf forests. Because their feet have shifted from one branch to
they are good climbers, they can access Female 0.6–2.7 ha
the next.
bird nests high in trees.
Identification The size and weight of possums varies
On offshore islands, Norway rats are greatly across New Zealand. Adult
Cat-sized marsupials with thick, bushy
large enough to kill burrow-nesting adult possums are 65–95 cm long and weigh
tails and body fur, pointed snouts, large,
seabirds and eat their eggs and chicks. between 1.4 and 6.4 kg.
fox-like tapering ears and brown eyes.
Possums are arboreal (live in trees) and
Possums in New Zealand have two main
have flexible ‘hands’ with five independent
colour forms – grey and black, with many
digits used for clasping branches and
variations in appearance.
holding leaves and other food when
Possums have three basic gaits – walking eating. Their ‘feet’ are similar except that
TOP
Ship rat eating a land snail. (along horizontal and gently-inclined the 2nd and 3rd digits are joined for most
Image: Ngā Manu Images © surfaces), half bounds (jumping from of their length and the first toe (‘thumb’) is
BELOW
branch to branch or up steeply inclined enlarged and has no claw.
A ship rat attacks a fantail/pīwakawaka at its nest. surfaces or through long grass) and bounds
Image: Ngā Manu Images © (on vertical surfaces such as tree trunks).
15 16Predator Free 2050 – A practical guide to trapping 4. Know your target predator
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| Possums
Habitat Behaviour Threat
Possums are nocturnal and can live Possums, while mainly herbivorous Possums have a significant impact
anywhere where there is shelter and a (feeding on leaves but also eating buds, on many of New Zealand’s natural
varied food supply. They are now flowers, fruit/berries and nectar) are ecosystems. They occur in high numbers
widespread across most of New Zealand. opportunistic omnivores, readily eating and their predators, mostly feral cats, do
Their preferred habitat is forest, and most food they come across in their not have much effect on controlling the
possum densities can be particularly high environment, including eggs, chicks size of the population.
in podocarp-broadleaf forests. The margins and invertebrates. While leaves are the main part of their
where forest meets pasture can also They are nocturnal and usually venture diet, possums will frequently eat other
support very dense populations. out of their dens to feed just after sunset. parts of trees or plants (including the
They spend most of their time in trees buds, shoots, flowers and fruit), which can Healthy rātā, Upper Copland. Image: Andris Apse
and approx. 10–15% of their time on lead to significant adverse effects on the
the ground. life cycles of targeted trees and plants.
Possums communicate primarily by Possums often have ‘favourites’ (such
smell – scent-marking tree trunks with as mistletoe, rātā, tree fuschia or kāmahi
oil from special glands along with urine trees), leading to an even greater impact
and droppings. They also make a range on these species. They also compete with
of sounds, including screeches, grunts, native birds and reptiles for food sources
growls, hisses and chatters. such as nectar.
They live in dens, preferably in tree In 1993, possums were filmed eating
branches or trunks, but also in ceiling the eggs and chicks of kōkako and this
cavities of buildings. Individual possums evidence changed many people’s views
may have several dens and change dens of the threat they posed to wildlife. They
several times per night. However, the dens eat invertebrates, including wētā, and are Possum browse on northern rātā and rimu, Castle
significant predators of New Zealand land Rock, Coromandel, March 2000. Image: DOC
are not exclusive, with more than one
possum using them, but generally not at snails (such as Powelliphanta spp.). They
the same time. often occupy holes in tree trunks for their
dens which would otherwise be
Juvenile females will establish territories
used by nesting birds such as kākāriki
close to their mothers, but juvenile
and saddlebacks.
Possum scavenges an egg at a kererū nest. males shift further away. Male possums
Image: Nga Manu images © prospecting new territories are often Dairy and deer farmers have the added
caught in traps. worry of possums spreading bovine
tuberculosis (Tb). The value of economic
Larger, heavier possums are more
losses in primary production associated
dominant, and females will dominate
with damage from and control of possums
similar-sized males
is in the tens of millions of dollars.
The main breeding season is autumn but,
in some locations, a second breeding
season occurs in spring. Usually only
one ‘joey’ is born at a time, though twins
do occur occasionally. Young possums
become independent at 6–9 months old.
17 18Predator Free 2050 – A practical guide to trapping 5. MonitoringXxxxxxxxxxxxx
before trapping
What is the difference between monitoring outcomes
5. Monitoring before trapping and monitoring results?
Monitoring outcomes Indicator species are species that are
Monitoring needs will vary depending on your site sensitive to predators or browsing threat and
Monitoring the native species you are trying
are representative of the other organisms in
to protect is known as monitoring outcomes.
The following section describes DOC best- the ecosystem, easily observable and able
These are the outcomes you hope to
practice monitoring techniques that may not to be sampled. They make a great choice
achieve by delivering predator control at
be practical for all sites. Monitoring is highly for monitoring outcomes because if they are
your site. You will start by monitoring what
recommended for larger trap networks to doing well then the less-sensitive species
species you have at your site and measuring
inform changes over time and to assist are likely to be improving in numbers as
the numbers that are present before you
with funding applications. For small sites well. Examples of indicator species include
start your predator control. This is your
and backyard trapping, monitoring is not kererū, tree wētā, bellbirds and tree fuchsia.
baseline measurement that will show if your
essential, but 5-minute bird counts and predator control is working. An increase in Whatever species you decide to monitor,
homemade tracking tunnels/chew cards native species at your site after predator there will be a monitoring method available.
can be a fun activity for families. control can be instrumental in ensuring You may need to discuss what you should
Before you start monitoring, contact your successful funding applications and for be monitoring, and how, with an appropriate
local DOC office, council office or pest promoting your group. expert. Five-minute bird counts are a
Kererū can be a good indicator species to monitor.
control expert for advice. Trapping is not commonly used method for monitoring bird
Image: Shellie Evans © Now you have finished your initial monitoring
just about how many animals you catch numbers. They are an easy way to find out
and established what wildlife you need
in traps. It is important to understand the which native birds are present and to monitor
You need to monitor native species to: to protect at your site you can work on
outcomes you are trying to achieve before them over time.
an outcome statement. This will help you
you commence a new trapping programme. determine what type of traps you will need
decide which predators you need to target Foliar Browse Index can be used to assess
This means monitoring what is present identify which native species are present to achieve your desired outcomes. the condition of plants. This technique looks
before you start as well as what and in what numbers
at the impacts of possums on forest health
happens after. define and track progress toward the Examples of outcome statements could be:
using indicator species, eg tree fuchsia.
desired outcomes for your project 1. increased kiwi chick survival rates
Other methods are available for lizards,
Why monitor? compare the health of your site with that
2. regeneration of the forest canopy.
invertebrates, bats, etc.
Monitoring assesses changes over time of others around New Zealand We know the biggest threat to kiwi chick
in ecological aspects of the area you are Whatever monitoring technique you select
evaluate success and know when you survival is stoat predation, so for outcome
trapping and is essential for determining it must be applied consistently so that
have reached certain targets statement 1 you will be setting up best-
how your trapping efforts are contributing the data collected is accurate and the
build a sense of achievement. practice predator control for stoats.
to improvements in the area’s ecology. studies can be replicated over time. It is
If our aim in outcome statement 2 is advised that you complete training in these
Examples of what should be monitored You need to monitor mammalian
regenerating forest canopy then you would monitoring techniques to ensure your results
include numbers of pests, numbers and predators to:
target possums and initiate best-practice are accurate. For more information on
species of birds present and vegetation determine which predators are present appropriate courses, visit www.doc.govt.nz
trapping for possum control.
growth at your site. Monitoring should be and in what numbers or www.nmit.ac.nz
a key component for anyone undertaking identify pest invasions
trapping as part of an ecological modify how you work (eg increasing or
restoration project. decreasing trap numbers and/or checking
frequency because your monitoring
results are demonstrating certain trends).
19 20Predator Free 2050 – A practical guide to trapping 5. Monitoring before trapping | How to use tracking tunnels to monitor stoats
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and rats
Monitoring results If you suspect ferrets at your site, contact Layout avoid any bias is to randomise the direction
your local DOC office or pest control expert For rodents, 10 tunnels per line spaced of your tunnel lines. A simple method for
Monitoring results refers to the monitoring
for advice. 50 m apart and at least 200 m between doing this is to roll a six-sided die (dice) and
of predator/pest numbers on your site. You
If you only want pest/predator data at tunnel lines at their closest point. the number rolled determines the compass
will measure the number of predators by
critical times, you could monitor during bearing from the start point along which the
monitoring them before you start and on For stoats, 5 tunnels per line spaced
bird breeding seasons or before and after line is set out (Table 4). Run the line in the
a regular basis once your predator control 100 m apart and at least 1000 m between
control operations. most practicable of the two bearings (either
is underway. This allows you to see if your tunnel lines at their closest point.
east or west) from the designated start
predator control is working. You can use the same installed lines for
For ongoing studies, monitor four times per point. If you can’t decide which to choose,
year: February, May, August and November. either rodent or stoat monitoring (if lines roll the die again. Pick the westerly bearing
The most common methods of monitoring
are at least 1000 m apart for stoats) by if the result is an odd number; pick the
are tracking tunnels for stoats, weasels
For a clearer picture of fluctuations across using every 2nd tunnel when monitoring easterly if the result is an even number.
and rats, and chew cards or wax tags for
the year, monitor once per month or every stoats on a 10-tunnel ‘rodent’ line.
possums (and sometimes rats).
two months. Don’t place lines in a grid but do run each
Monitoring ferrets is difficult due to the size one straight in a single direction.
of tunnels. Trail cameras are an effective, Select places to install tracking tunnels Table 4. Suggested method for determining
yet expensive, way to monitor them. that represent the range of ecological the direction (compass bearing) of each tracking
types in your trapping area. For example, tunnel line
if 50% of your area is beech forest,
How to use tracking tunnels to monitor stoats and rats put 50% of your monitoring lines in Angle of tunnel line
Die roll
beech forest. (magnetic)
Step 1 – Planning Exclude bias 1 285°W – 105°E
Estimate the size of your trapping area When setting out tracking tunnel lines it is
very important to ensure that representative 2 315°W – 135°E
The number of tracking tunnel lines you will need to adequately monitor target animals is
environments are sampled within the areas
dependent on the size of the area being trapped (Table 3). 3 345°W – 165°E
you are interested in (eg a rodent control
block). The easiest way to do this is to 4 15°E – 195°W
Table 3. Suggested number of tracking tunnel lines to use for surveying both mustelids and rodents
consider the gross environment types that
make up your study site or management 5 45°E – 225°W
Approximate 1,200–
300– 600– 900– block and what proportion of that area they
area to be ≤ 300 ha 10,000 > 10,000 ha
600 ha 900 ha 1,200 ha make up. 6 75°E – 255°W
surveyed ha
For example, if 50% of your study area is
Suggested red beech forest, then 50% of your sampling
20 Frequency of running tracking lines
number of effort should include that environment.
(or more if
tracking 6–8 8–10 10–12 12–15 15–20 Use your outcome and management
logistically The start points for each line should be
tunnel lines objectives to inform monitoring frequency,
feasible) determined by environment type, access,
for rodents for example:
logistics (all lines need to be serviced on the
Suggested same day) and the distance away from the for ongoing studies for rodents, monitor
15
number of next nearest tunnel line. four times per year: February, May, August
(or more if
tracking 4–5 6–7 7–8 9–10 10–15 When determining the direction of tunnel and November
logistically
tunnel lines for line runs, avoid running lines entirely along
feasible) for ongoing studies for stoats, it is
mustelids
geographic features (eg roads, ridgelines recommended as a minimum you should
or streams) or other potential sources of run surveys in November, December,
* This table is reproduced from 'DOC tracking tunnel guide v2.5.2: using tracking tunnels to monitor rodents and
mustelids'. www.doc.govt.nz/Documents/Science-and-technical/inventory-monitoring/im-toolbox-animal- bias (eg bait station lines). The best way to January and February.
pests-using-tracking-tunnels-to-monitor-rodents-and-mustelids.pdf
21 22Predator Free 2050 – A practical guide to trapping 5. Monitoring before trapping | How to use tracking tunnels to monitor stoats
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and rats
Step 2 – How to make tracking tunnels
Each tracking tunnel consists of a wooden base with a black plastic ‘corflute’ cover. Corflute
is the material used for real estate signs; it is cheap, light in weight and reasonably rigid. In
most cases these tunnels are quite resistant to interference and damage by other animals.
However, if kea, weka or possum interference is so bad that it is compromising the amount
of data you are collecting from your surveys, then we suggest you use a sturdier exterior of
black polypropylene plastic or timber.
Tunnel dimensions and materials from a printer, as hand cutting can be
Wooden base: 100 mm (W) × 535 mm (L) very time consuming. The type of paper
plywood or 25 mm thick rough sawn pine may be determined by local availability
(Figs 1 and 2). (and cost), but ensure it is sufficiently
absorbent to retain the food colouring
Tunnel cover: black corflute, stapled or
animal prints.
nailed to the base, 615 mm (L) allows for
40 mm overhang each end of timber; Sponge: 173 mm (L) × 95 mm (W);
tunnel internal clearance height should be 3–5 mm thick.
100 mm (Figs 1 and 2). Tracking media: use liquid red (Amaranth Figure 2. Black corflute tracking tunnel
123) food colouring at approximately cover and wooden base – end view showing
Polycarbonate trays: 520 mm (L) × 95 mm
tunnel dimensions.
(W), with each of the three partitions being 1:3 dilution in water. In extremely dry
173 mm (L) (Fig. 3). conditions or where you think freezing
is likely to be an issue, mix the food
Papers: each paper should be pre-cut
colouring and water solution with
to 173 mm (L) × 95 mm (W) (Fig. 3). We
polyethylene glycol (approximately 20%).
strongly suggest you source this pre-cut
Figure 1. Black corflute tracking tunnel cover and
Figure 3. Tracking tunnel tray showing
wooden base, showing tunnel dimensions. Also
paper/card and tracking ink tray.
shown is the location for smearing peanut butter on
the vertical face of the wooden base at each end of
the tunnel for rodent surveys.
23 24Predator Free 2050 – A practical guide to trapping 5. Monitoring before trapping | How to use tracking tunnels to monitor stoats
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and rats
Step 3 – Laying the tracking tunnels Step 4 – Laying out tracking cards
Install unset tracking tunnels at least 3 weeks before your first survey. Resident animals You will need two days of good weather before you lay the tracking cards into tunnels.
should be familiar with them before you start monitoring. Leave the tracking tunnels in place Weather affects animal activities and may affect your results. Conduct your monitoring
between surveys. survey over 1 (clear) night for the rodent monitoring index and over 3 nights for the mustelid
monitoring index.
Equipment 2. Leave the tunnels in place between
Tracking tunnels, unassembled and survey sessions.
Day 1: Laying out tunnels Day 2 or 4: Processing tunnels
bundled in groups of 10, plus any 3. Mark the tunnel locations with flagging
necessary tools. Make your own tracking tape (or, if you have the funds, use Equipment list Processing of tunnels will occur on day 2
tunnels or buy them. permanent plastic triangle track markers). Pre-inked or home-made tracking cards. for rodents and day 4 for mustelids.
Tunnel pegs – No. 8 wire loops, two Since the tunnels are left in situ between
Bait: peanut butter for rodents, fresh meat Equipment list
per tunnel. surveys (in some cases for several years),
or earyze for mustelids.
their locations need to be well marked. Notebook, pencil.
Waterproof marker pen. Tools if monitoring any fixed-lid tunnels.
When using flagging tape to mark tracks Optional: smartphone to record results.
Plastic markers and flagging tape, two it is a good idea to use one colour to mark Personal gear.
colours (pink is a popular choice for pest Tools if monitoring any fixed-lid tunnels.
the track and another to mark the tunnel.
line markers. Don’t use orange – it’s the How to set a tracking tunnel Personal gear.
4. Write each tunnel number on the flagging-
colour used on recreational tracks). Remove any scat or detritus from
tape or plastic triangle at the tunnel site Process each tunnel in the field
Hammer and nails. with a permanent marker pen. the tunnel.
1. Remove the bait.
GPS preloaded with start points, map. 5. Assemble the tunnels as you put them Write the number of the tracking tunnel
and the date the card is placed in the 2. Remove pre-inked tracking card and
Either GPS or a compass and distance- out in the field. It is a lot easier to carry
tunnel on front of card. fold closed.
measuring tool (eg hip chain or non- the separate bases, trays and pre-cut
stretch cord) to mark locations of lines Place the fresh pre-inked tracking card in 3. Write the tunnel number and date
unfolded corflute for 10 tunnels than it is
and tunnels. the tunnel, unfolded. collected on the card.
to carry 10 fully assembled tunnels.
Personal gear. In areas where weka are present use pins 4. Keep the cards in order as you collect them.
6. Site each tunnel at the most suitable spot
(ie a place that look like it would provide a at either end to fix the paper. 5. Make notes.
Mark each line If there are no tracks, record whether
good ‘run’ for small mammals) within 2 m For the rodent surveys, smear peanut butter
Use your GPS device or map to locate the of the 50-m marker along the survey line. generously on either end of the tracking the bait was taken.
line’s start point. If you’ve mastered footprint identification,
7. If you have made your own tracking cards, card. Place baited cards in each of the 10
Follow the randomly-generated compass place the tunnel on reasonably level tunnels spaced 50 m apart along the survey you can do that now or back at base.
bearing for the line and measure the line. Collect the cards after 1 night. If there’s fresh scat in the tunnel,
ground, as this will reduce the chances
distance travelled. of the food colouring running from the identify it and note the species as
For mustelid surveys, place the meat bait present just as if footprints were
Place markers and/or flagging tape along middle sponge tray and flooding the
in the centre of the inked central area of the present. Remove the scat.
the line to make it easy and safe to follow. paper on the downhill side.
card. Place cards in each of five tunnels Note anything else unusual, such as
Label them with the line’s identifier. 8. Ensure that the tunnel is held firmly in spaced 100 m apart along the line – this tunnel disturbance.
place by pegging it down with two No. 8 could be every 2nd tunnel of the established
Setting out tunnels and lines
wire hoops. This is particularly important tracking tunnel line with 10 card tunnels Finish processing back at your base
1. Set out the tunnels at least 3 weeks in areas were disturbance by possums at 50 m intervals (as it is common to use 1. Spread any damp papers out to dry.
(ideally longer if you plan to survey is likely to be a problem and especially ‘rodent’ tracking tunnel lines for conducting 2. Identify and double check any
mustelids) prior to the first survey session important if you plan to use the tunnels to mustelid surveys). Collect the cards after predator footprints.
to ensure any resident animals are monitor mustelids. 3 nights.
conditioned to the presence of 3. Update your notes.
9. Check that access to both ends of the
the tunnels. 4. Bundle the papers, label with the
tunnel is unobstructed.
survey area and date, and store for
later reference.
25 26Predator Free 2050 – A practical guide to trapping 5. Monitoring before trapping | How to use chew cards or wax tags to monitor
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possums
How to use chew cards or wax tags to
monitor possums
Step 1 – Planning Exclude bias
For sampling to be unbiased, all potential
Estimate the size of your trapping area possum habitat must have an equal
The number of chew cards or wax tags chance of being sampled.
you will need to adequately monitor target If the start point for a line (generated by
animals is dependent on the size of the the random selection process; see p. 22)
area being trapped. Set up temporary wax is the same as one used in previous
tag or chew card lines to monitor possum monitoring, it is acceptable to use that
numbers. Use your results to track progress start point again provided the prior
and make improvements. monitoring was carried out more than
6 months previously.
Calculate the number of lines required for
Overlay a numbered grid (intervals no
different trapping area sizes:
greater than 100 m) over the map of
500 ha: 10 lines
the sampling area. Then use random
500–700 ha: 11 lines northings and eastings to generate
700–900 ha: 12 lines random coordinates. These are the start
900–1100 ha: 13 lines point locations for the lines. Mark in the
1100–1300 ha: 14 lines
lines from the random start points at zero
degrees magnetic. Discard any line that
1300 ha or more: add 1 line per each
falls either wholly or partly outside the
additional 200 ha; up to 60 lines.
sampling area, or within 200 m of any
Layout previously selected line.
A tracking tunnel is baited with peanut butter. Image: DOC
10 devices per line. Alternatively, a GPS can be used to select
random coordinates in a given area.
Run each line straight in a single direction.
Keep devices 20 m apart on each line and Frequency of laying out chew cards or
at least 200 m from the nearest monitoring wax tags
line at its closest point. Use your goal and management objectives
to inform monitoring frequency.
For example:
before and after possum control in order
to determine how effective control has
been and if it has achieved a target result
annually to see if possum abundance is
below a level required to protect valued or
indicator species.
Tracking tunnel card showing prints. Image: DOC
27 28Predator Free 2050 – A practical guide to trapping 5. Monitoring before trapping | How to use chew cards or wax tags to monitor
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possums
Step 2 – Laying out chew cards or wax tags Place and mark each chew card or Step 3 – Collecting chew cards
wax tag or wax tags
Both chew cards and wax tags rely on bite mark identification for successful monitoring
Every 20 m, place a device and collect
of animals. You’ll need seven consecutive nights of reasonable weather, with no heavy After seven nights, collect the devices and
your measuring line.
or prolonged rain. Pre-labelling the chew cards or wax tags with both the line and device process them.
number can be easier than doing it in the field. To place a wax tag:
Collect the flagging tape – you will set
mount wax tag and luminescent strip on different lines next time.
Equipment Working from one end to about the same nail 30 cm above the ground
Collect the devices, making sure they're
5 cm in, use a paint scraper to push a with the wax block facing the ground. If
Chew cards or wax tags grouped in labelled correctly.
tablespoon of peanut butter about there are no trees, use a post
bundles of 10. Process and record the results:
2 cm into the flutes. Make sure to get an take a handful of lure and smear it up
If using wax tags: luminescent strips plus (P) Definite possum bite marks
even spread. the trunk of the tree to make a 10-cm-
lure (1 part icing sugar to 5 parts flour).
Flip the block over and do the same at wide blaze that finishes behind the tag. (NT) Non-target but identifiable bite
You can make your own chew cards from marks. Record the species too
the diagonally opposite corner. To place a chew card:
3 mm white corflute.
If your area has a high density of rats, fold a card in half (U) Unknown bite marks
Cut corflute into 9 x 18 cm pieces so
only apply the peanut butter to one side push a nail through the top layer 10 mm leave the record blank if there are no
that the flutes are 9 cm long.
of the card. from the fold and through the bottom bite marks
Bait with smooth peanut butter.
Waterproof marker pen. layer 5 mm from the fold. This will keep (L) Lost or destroyed device.
Bundle 20 chew cards together to form
Flagging tape (pink is a popular choice the card open at 90° Store the devices for at least 2 years.
a temporary block.
for pest lines. Don’t use orange – it’s the hold the card in place on a tree, 30 cm For further information on planning
Stand the block of cards so that the colour used on recreational tracks). above the ground with the fold at the and conducting possum population
many flute openings along the long
Hammer and 50 mm flathead nails. top. If there are no trees, use a post monitoring, refer to ‘Possum population
edge are facing up.
Wooden posts if monitoring in hammer the nail down into the tree monitoring using the trap catch, waxtag
open country. at 30°. and chew card methods’, available at
Label the device clearly with the line and www.bionet.nz/library/npca-
Compass and distance measuring tool
location identifiers. publications/
(eg hip chain or non-stretch cord).
Personal gear. Mark the location on your GPS device.
Continue until you’ve installed 10 devices.
Mark each line
List of start points (compass bearing is
predetermined and the same for each line,
use zero degrees magnetic as a default).
Follow the predetermined compass
bearing for the line and measure the
distance travelled.
Place flagging tape along the line to make
it easy and safe to follow. Label the tape
with the line’s identifier.
Wax tag with lure smear. Image: Possumz © Chew card with bait applied. Image: Traps.co.nz © A nibbled chew card. Image: Kiwi Coast Project ©
29 30Predator Free 2050 – A practical guide to trapping 6. Select
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the right trap
Interpret the data for tracking tunnels, chew cards
and wax tags 6. Select the right trap
Several factors will influence your selection of traps for your networks:
target predator non-target species type of terrain
efficacy of trap capacity of volunteers budget constraints.
humane killing ease of use (especially trap setting)
Stoat footprints on a tracking card. Image: DOC
To calculate and monitor the abundance of write a data report to share. Include the
pests over time, you can: following information:
name and location of trapping area
use apps or online data management
agencies to generate indices, maps and size of the trapping site
summary tables to export and share. You control methods and start and Trapping at North Head, Auckland. Image: DOC
can also use these apps in the field finish dates
use scientific formulae to generate indices device type NAWAC (National Animal Welfare Advisory Committee)
yourself: www.bionet.nz number of lines
interpret footprint tracking tunnels: The following information relates to the Agriculture to recommend to the Governor-
number of nights devices were deployed
welfare performance of traps used in New General traps that should be prohibited
guide to reading footprint tracking weather information Zealand for capturing and/or killing small to because they cause unacceptable pain and
tunnels: www.landcareresearch.co.nz names of participants (optional –
medium-sized mammals. The tests relate to suffering. To enable the welfare performance
DOC tracking tunnel guide get permission) the welfare performance of the traps, NOT of traps to be assessed in a standardised
interpret bite marks: maps with data overlays (optional). to their capture efficiency, safety, costs, or way, the National Animal Welfare Advisory
for wax tags: www.traps.co.nz target specificity. Committee (NAWAC) has developed a
for chew cards: trap-testing guideline. The NAWAC kill trap
In New Zealand, trap use is regulated by test requires 10/10 test animals are to be
www.landcareresearch.co.nz the Animal Welfare Act 1999. This Act rendered irreversibly unconscious within 3
permits any trap to be used for trapping any minutes to meet the guideline for acceptable
species, but it also enables the Minister of performance (Table 5).
31 32You can also read
