Thomas, B.; R. Taylor, P. Dunlevy, K. Mouritsen, and J. Kemp. The Ka Mate reverse-bait snap trap – a promising new development
The Ka Mate reverse-bait snap trap – a promising new development
B. Thomas¹, R. Taylor², P. Dunlevy³, K. Mouritsen4, and J. Kemp5
¹Ka Mate Traps Ltd, 190 Collingwood St., Nelson 7010, New Zealand. <[email protected]>. ²13 Templemore
Drive, Richmond 7020, New Zealand. ³USDA-APHIS Wildlife Services, 3375 Koapaka Street, Honolulu, HI 96819,
USA. 4 Waiaro Sanctuary, P.O. Box 6, Colville 3584, New Zealand. 5 Department of Conservation, Private Bag 5,
Nelson 7042, New Zealand.
Abstract Development, field trials and potential of Ka Mate reverse-bait snap trap are described. Prototypes were tested
on five species of rodents in a range of environments in New Zealand, Alaska, Hawaii, Wake Atoll, Wallis & Futuna
Islands, New Caledonia and Seychelles. Paired testing of reverse-bait traps in close proximity to treadle traps was found
to be inappropriate because trap function combined with animal behaviour skewed results. The first factory product, the
Ka Mate medium “safeTcatch” trap, the corflute “flatpack” trap station and various wax baits are now under evaluation
by professional conservation and science practitioners worldwide. One example is Waiaro Sanctuary (Coromandel, New
Zealand) where in one year, using only Ka Mate rat traps, 75 ha of forest yielded 656 rats, reducing population indices
from 100% tracking tunnel rates to 10%. Data indicates that over 95% of rats were trapped with head/neck strikes, and
only one bird was caught in Waiaro in circa 90,000 trap nights using Ka Mate traps set unprotected on the forest floor.
Keywords: Ka Mate traps, reverse-bait snap trap, treadle trap, Victor, Catchmaster, Ezeset, Mus, Rattus, Wake Atoll,
Wallis and Futuna Island, Waiaro Sanctuary, New Zealand.
INTRODUCTION
Advances worldwide in rodent control or eradication
on islands during the past three decades have centred on
the use of rodenticides (Howald et al. 2007). However, the
propensity for rodents to develop a tolerance for toxicants
(Bailey and Eason 2000) and increasing public opposition
to use of poisons may limit their continued use, particularly
in mainland situations (Williams 1994; Towns and Broome
2003; Mason and Littin 2003; Towns et al. 2006). Traps
have similarly evolved in design and strategic use but they
also attract a public opposition, ostensibly over animal
welfare issues.
The New Zealand Department of Conservation
(DOC) requires a better performing snap trap that gives
more consistent catch/kill rates; improved animal welfare
outcomes; less non-target catch and environmental
interference; enable higher quality trapping data; have
greater durability; less maintenance; quicker servicing
during routine checks; and are easier for operators to use
than current preferred rodent traps. In short, better returns
from traps in relation to money expended (Keith Broome
pers. comm., April 2004).
In this paper, we describe the development and field
trials of Ka Mate (KMT) reverse-bait snap traps, which
have been designed to meet modern efficacy and animal
welfare requirements.
Traditional, wooden based “break-back” traps (snap
traps), have been used in New Zealand since at least 1920,
particularly for bio-security at ports, rodent control around
factories, and as a health measure in urban environments
(Wodzicki 1950). They have also been used internationally
for scientific data collection and in conservation management
programmes (Bull 1946; Watson 1956; Wodzicki 1969;
Daniel 1973; Innes et al. 1995; Dunlevy et al. 2000; Efford
et. al. 2006; Malcolm et al. 2008; Theuerkauf et al. 2010).
More recently, snap traps have been employed in many
large-scale New Zealand mainland island rodent control
programmes (Saunders 2000, 2003; Speedy et al. 2007;
Ogden and Gilbert 2008) and as adjuncts to toxicants in
island eradication campaigns (Morrell et al. 1991; Taylor
et al. 2000; Merton et al. 2002; Thomas and Taylor 2002;
MacKay and Russell 2005; Nugent et al. 2007; Witmer and
Burke 2007; Varnham 2010).
Rats have been eradicated from at least two islands of
up to 21 ha with snap traps (Moors 1985; MacKay and
Russell 2005; Howald et al. 2007), but trapping is usually
considered to be too labour intensive and expensive as a
sole eradication technique for rats (Keith Broome pers.
comm.). Poor trap performance has exacerbated negative
public attitudes, resulting in stricter rules for trapping and
animal welfare now embedded in policy and law (Mason
and Litten 2003; Powell and Proulx 2003; Litten et al.
2004).
Traps have traditionally varied from toggle trigger traps
with a small (baited) trigger to large treadle plate designs
that use a lure to entice target species to step onto a plate to
spring the device. Treadle snap traps are generally easier to
use than trigger traps. Many trap designs are operationally
unstable and not robust enough to withstand the rigours of
long term field use. Baseboards on wooden models warp
or split, staples pull and weak points on plastic variations
soon break. The larger trigger area of treadle traps makes
them more prone to misfire due to environmental events
and the presence of non target species.
THE KA MATE REVERSE-BAITING SNAP TRAP
Trap development
During the mid-1980s, two of us (RT and BT)
experimented with ways to improve snap trap efficiency.
Modifications were made to wooden based trigger “Ezeset”
traps being used to catch Norway rats (Rattus norvegicus)
which led to “reverse-baiting” snap traps with dense,
supportive bait beneath rather than on top of the trap trigger.
This utilised the bait as a removable structural component
of the trap, introducing significantly more stability into the
trigger function.
Six steel reverse-bait snap traps were then engineered
in 2003 and of the five ship rats (Rattus rattus) these first
killed, three were cranial and two were humane neck strikes.
Fifty of these traps were subsequently incorporated into a 6
month paired trial with “Victor Professional” traps at Weka
Bush, Nelson Lakes National Park. In 2005, 100 handmade
aluminium prototypes (Fig. 1), which we called Ka Mate
(KMT) traps, were integrated with the steel traps into an
alternating trap trial with “Victor Professional” rat traps
and tested over 13 months in Nelson Lakes Big Bush rodent
control area. Another 100 KMT prototypes were included
in an alternating trap trial with Victor Professional rat traps
in DOC’s 2005 trap research programme in Te Urewera
National Park.
The KMT traps caught and killed mice (Mus musculus),
rats (Rattus rattus), weasels (Mustela nivalis), stoats
(M. erminea) and hedgehogs (Erinaceus europaeus). In
the Te Urewera trial, the KMT traps also had far fewer
Pages 233-238 In: Veitch, C. R.; Clout, M. N. and Towns, D. R. (eds.). 2011. Island invasives: eradication and management.
IUCN, Gland, Switzerland.
233
Island invasives: eradication and management
Fig. 1 Relative condition of Ka Mate prototype (left)
and Victor Professional (right) after equal environmental
exposure at adjacent sites in the Big Bush trap trial.
unsprung/bait missing events than Victor traps (2 versus
71, respectively), indicating that the reverse-bait trigger
reduced problems with non-target and environmental
triggering. When compared with wooden-based wire striker
traps, operators also found the aluminium KMT to be the
safest to set and handle, easiest to clean and maintain (Fig.
1), required the least service time during routine checks,
and had the greatest durability in the field (Paton et al.
2007; Morriss et al. 2007; Moorcroft et al. 2010).
In August 2005 on the Seychelles Islands, Gideon
Climo (pers. comm.) undertook three 2 hour evening
trapping sessions using six KMT prototype traps, which
were systematically set, checked, cleared and rebaited
with coconut on a rotational basis. He caught over 60 ship
rats, achieving 100% humane head and neck strikes on the
adults and predominantly shoulder and mid torso strikes
on small rats.
The first Norway rat (R. norvegicus) caught in a KMT
prototype was on Adak Island, Alaska in May 2006. The
technician reported “a perfect kill just behind the eyes” and
that the unprotected traps remained set and continued to
catch after exposure to “gales whipping vegetation, deluges
of rain and burial in snow” (Lisa Spitler pers. comm.).
On Wake Atoll in October 2007, BT and PD established
a 200 x 200 m trapping grid for rats consisting of 100 traps
spaced at 20 m. Fifty KMT prototypes formed a central core
within the grid and were surrounded by 50 Catchmaster
(CM) wooden based trigger traps modified to operate as
“treadle” traps. Midway through the trial an extra 32 CM
traps were added to the periphery, creating double trap sets
on three sides of the grid. All traps were tacked to plywood
base boards, placed unprotected on the ground and baited
with cubes of fresh coconut. The grid was checked and
serviced morning and late afternoon, totalling 13 check
periods over 7 days. Wake had a high density rat population
and a total of 549 rats (520 R. exulans and 29 R. tanezumi)
were caught ─ 297 from 650 individual KMT trap checks
and 252 from 810 individual CM trap checks. KMT traps
scored 157 head/neck strikes to 125 body strikes, whereas
CM traps scored 94 head/neck strikes to 152 body strikes
and both trap types recorded low numbers of limb and tail
strikes. Non-catch interference also varied between trap
types, with KMT recording 85 traps sprung/empty and
13 traps set/bait missing, compared to CM with100 traps
sprung/empty and 172 traps set/bait missing. Hermit crabs
were the only non-targets caught, 6 in KMT and 22 in CM
(BT & PD unpublished data). Clearly the KMT traps outperformed the CM traps on Wake, scoring higher catch
rates to trap check ratios and a greater percentage of head
and neck strikes. The considerable disparity in trap set/
bait missing totals is hugely significant, especially since
234
Fig. 2 Ka Mate “safeTcatch” trap - with trigger cowling and
wax bait.
it was mechanical malfunction (rectified in seconds with a
file) that caused the problem in the small number of KMT
traps afflicted whereas learned avoidance behaviour by rats
was the cause with the CM traps.
From 2007-2010, KMT prototype traps were used in
ecological surveys on New Caledonia, Wallis and Futuna
Islands (Theuerkauf et.al 2010) and in trials to test the
efficacy of unprotected KMT traps against “Ezeset”
wooden based trigger traps on Pacific, ship, and Norway
rats (Theuerkauf et.al 2011). These studies concluded
from C. 2900 trap nights that KMT traps were the more
effective against rats > 100 g (i.e. predominantly ship and
Norway rats), whereas “Ezeset” traps were more effective
against rats < 100 g (predominantly Pacific rats). A high
percentage of “Ezeset” traps were sprung by heavy rain
but rain had no effect on the KMT traps, which maintained
a significantly higher percentage of operational traps
throughout the trials. The durability of the KMT traps was
considered an advantage for long term field use.
The “safeTcatch” rat trap
The first commercial KMT trap to be produced was the
“safeTcatch” (“sTc”) rat trap (Fig. 2), which incorporates
a safe set mechanism and is currently available from KMT
Ltd, Nelson, NZ. The traps are constructed from extruded
aluminium with stainless steel shafts and fasteners and
double sprung with galvanised springs. Bar catches that
engage when arming the trap work in conjunction with
the wide retainer arm that automatically releases the safety
Fig. 3 Typical humane head strike - ship rat in unprotected
Ka Mate “sTc” trap.
Thomas et al.: Ka Mate snap trap
catch during setting, which makes the process easier for
those with weaker hand strength. The traps are supported
with replacement parts, which means that KMT traps can
be easily repaired, upgraded or converted as design of
component parts develops to improve trigger configuration
or to suit a different target species. Replacement of any part
can be easily undertaken using a simple custom-designed
trap tool, so there is no reason to discard a whole trap.
A detachable plastic trigger cowl forces rats to take
the bait from the front of the trap, ensuring a humane
head strike (Fig. 3) while reducing potential for learned
trap avoidance. Baits held firmly beneath the curve in the
trigger ensure the trap will not trigger prematurely when
knocked or when non-target species such as lizards, birds,
or small mammals walk, crawl, or bounce on the trigger.
Since it requires a concerted effort by the rat to remove
the bait from beneath the trigger (which can cause the
trap to move), it is essential that the trap be restrained for
maximum efficiency. Holes are therefore provided in the
base for spikes, screws or ties, which enable it to be secured
to a backing board or either horizontally or vertically to a
natural substrate. The operational stability inherent in the
design of the trap (especially the trigger function) reduces
spontaneous misfire and by-catch and the simple trap setting
procedure minimises operator bias between trappers.
Ka Mate “flat-pack” protective station
Protective covers are used with traps to restrict entry by
non-target fauna and to protect the baits, but many covers
in use are bulky, heavy, flimsy or difficult to access. Ka
Mate has produced a trap station fabricated in one-piece
from “Corflute” cellular plastic sheeting. KMT “flat pack”
stations fold compactly for storage and transport and have
a lid that provides easy access (Figs. 4 and 5).
The stations have entrances on each side at one end for
rats and centrally placed for mice, which provide alternative
avenues for entry or escape and create a 90 degree entry
angle that reduces the reach of non-target birds. When
stations are fixed with stakes or weighted with rocks on
the side flaps, target species can enter and walk up to the
trap on natural substrate. Decomposing carcases suppurate
directly into the ground. Alternatively, KMT stations and
traps can be screwed vertically onto trees/posts/walls at
a height that allows target species easy access. When set
vertically, the rats are confined to a smaller floor space,
preventing pull back as the trap triggers and enhancing
catch effectiveness (Fig. 5).
Fig. 4 Corflute “flatpack” trap-station (assembled for use
and folded for storage).
Bait development
The bait is crucial to the function of Ka Mate traps and
requires removal by a positive twist or tug to extract it from
beneath the trigger to spring the trap. Rodents invariably
take baits by mouth, which ensures the animals’ head is
in an optimum position to achieve an efficient fatal head
strike. Bait can be household food items, such as hazel
nuts, brazil nuts, walnuts, dog and cat pellets, chocolate,
dried cheese and cubes of fresh coconut, or any other food
firm enough to support the downwards pressure of the
trigger. KMT has also developed and tested purpose-built
baits using “Pestoff” non-toxic pre feed (Animal Products,
Wanganui) as a base ingredient. When mixed into palm
nut wax with different flavoured additives, the baits can
be moulded into plugs of optimum shape and size to fit
the KMT trigger (Fig. 2). These baits can be effective for
up to a month in dry conditions, but earlier replacement is
recommended.
Utilisation and user perception
When the Ka Mate “sTc” trap became available in
June 2008, prospective users such as community trapping
groups began undertaking trials to test the new traps. They
invariably set up proximately paired and/or alternating
trap trials with Victor Professional traps and early
anecdotal feedback indicated some disappointment over
KMT trap performance. The issues apparently arose from
long established practices associated with the operation
of traditional snap traps, which were problematic when
universally applied to Ka Mate traps. For example, trappers
assumed that baits placed under the extreme end of the
KMT trigger would be easier to remove (i.e. the equivalent
of hair triggering old style traps) and consequently improve
“sTc” trap performance. The practice instead exacerbated
the incidence of rats beating the striker, being injured by
a glancing blow or caught by a limb. It also increased
the chance of catching non-target species. Furthermore,
trappers often did not appreciate that the curved “sTc”
trigger that accommodates the bait is specifically designed
to slow rats down by forcing them to twist the bait sideways
to remove it, ensuring the head is in optimum position to
receive an efficient cranial strike.
Fig. 5 Vertically set “flatpack” station with the door open.
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Island invasives: eradication and management
Similarly, when several users complained that their
KMT traps were not achieving high catch rates, it transpired
that during service checks any traps found still set were
bypassed, with many baits unchanged for two or three
months. Contrary to common belief, rodents do not like
stale mouldy food and it is imperative that the bait on KMT
traps be replaced regularly.
Also, people placed new sterile KMT traps alongside
pre-used odour saturated treadle traps, creating an obvious
disadvantage for the KMT traps because of rats’ inherent
nervousness around new equipment. Neophobic behaviour
combined with differences in trap function (e.g., the
arbitrary depression of the treadle foot-plate vs conscious,
controlled reverse-trigger bait removal) tended to skew
the trials into a “race” to see which trap would catch the
same rat first. Trap catch data and observations made on
several occasions indicates that in most instances (unless
there is intense competitive pressure) it takes much longer
for rats to trigger a KMT trap than a large-plate treadle
trap. Rats have been seen to cautiously approach baited
Fig. 6 Waiaro grid layout and Year 1 tracking-tunnel results.
236
KMT traps several times, often from different angles,
before even putting a foot on them and they sometimes
departed altogether for several hours or overnight before
returning to check out a trap again. As their confidence
grew, they would on occasion mouth the bait several times
or nibble it a little before making the fatal decision to take
a firm hold and twist or pull it from beneath the trigger
(BT, RT, PD and Gideon Climo pers. obs., Baki Bakhshi
video recording). Many trappers fail to understand that the
most important function to test for in a new trap is not how
quickly it catches rats, but how effectively it kills them.
Since results from several of the field trials raised issues
with regard to the validity of proximal paired testing, we
considered a well planned, large scale trial was needed
to test the efficacy of the commercially produced KMT
“safeTcatch” rodent traps in isolation of other brands.
An opportunity for a major collaborative “trap trial by
management” arose in late 2008 using “sTc” traps for rat
control in a private eco-restoration project in Northern
Coromandel.
Thomas et al.: Ka Mate snap trap
WAIARO SANCTUARY TRAPPING PROGRAMME
Waiaro Sanctuary is private land in the Moehau Kiwi
Recovery zone, Moehau Forest, ten kilometres north of
Colville. The first phase goal of this new rodent trapping
programme was to achieve a toxin-free eradication of ship
rats, or to reduce and hold their densities at low levels (510% tracking tunnel indices) over a 75 ha block, using only
KMT traps.
A 75 ha grid was created with 427 single “sTc” rat
traps at 25 m intervals along 10 trap lines spaced 75 m
apart, with a perimeter line set along three sides of the
grid (Fig 6). Fifty of the perimeter traps were in protective
KMT “flatpack” stations. The rest of the traps were fitted
with plastic trigger cowls and secured, uncovered, by
being pinned to the ground or tied to tree roots. Five
index lines (10 tracking tunnels per line) were installed to
independently monitor trapping success, three within the
grid and two outside (Fig 6).
Traps were given time to weather and three applications
of Pestoff RS5 nontoxic pre-feed was hand broadcast
sequentially across the block, along trap lines and then in
close proximity to the traps only. The traps were then set
using KMT RS5 wax plug baits.
Fifteen full checks with all traps serviced in a 24-48 hr
period were completed in the 12 months from 22 January
2009 to 21 January 2010, the majority in the first 6 months.
Alternatively, progressive servicing was carried out line
by line over periods of a week to a month and in winter
service checks were restricted to perimeter lines only.
Head and neck strikes on adult rats were so consistent that
the field teams stopped recording the category, insisting
that the KMT traps were achieving “99%” humane kills,
including body blows to smaller rats (KM pers. obs.). Four
index tracking sessions were undertaken both inside and
outside the trapped area - two prior to trapping and two
during trapping.
The traps caught 656 rats, with index tracking
frequencies reduced from up to 100% before trapping
to 10% during the trapping period (Fig 6). An initial
knockdown of 299 rats was achieved in less than three
weeks with tallies rising to 558 at three months. A further
98 rats were caught during the next nine months with 15 of
these in the six weeks before the final January 2010 check
(Fig. 7) - a marked contrast to the 117 caught on night one
12 months earlier. The reduction of rats was substantial and
only one bird (not identified) and 81 mice were the bycatch from one year’s trapping (approx 90,000 trap nights)
in Waiaro Sanctuary with unprotected traps.
The RS5 wax plugs remained intact for more than a
month, but probably lost their attractiveness as bait for rats
much sooner. Operators found the KMT stations convenient
to install and access, and the traps easy to operate and
service.
DISCUSSION
Varied outcomes from the early field trials made it
difficult to determine what advantages the KMT prototypes
provided over the traditional trigger and treadle traps. As
the data base grew we began to speculate that rat behaviour
coupled with trap function was elemental to the different
catch rates being recorded between the trap types, the
main contributing factor being that it took rats longer to
spring a KMT trap than a traditional trigger or treadle
trap. The dense population of Pacific rats on Wake Atoll
coupled with the use of night vision equipment (plus the
mass of data this project generated) and Gideon Climo’s
trapping of ship rats in the Seychelles provided the first
opportunities to evaluate rat behaviour in conjunction with
KMT trap function from direct observation. Although we
have drawn our conclusions from all the studies, it is the
significant level of rat control achieved with Ka Mate traps
in Waiaro Sanctuary that verifies its potential when used
alone, unencumbered by the proximity of other trap types
(Fig. 7).
The functional stability of the reverse-bait trigger
generates a very consistent catch performance. The
percentage of quality-kill head and neck strikes can
be increased and environmentally generated misfire,
rodent induced trap disturbance, and non-target by-catch
significantly reduced when using KMT traps. Such results
minimise the opportunities for rats to learn trap avoidance
and reduces animal welfare issues. The simple standard
setting procedure of KMT traps eliminates operator bias
and improves population indexing.
The functional stability of KMT traps coupled with
trap durability enables traps to be screwed vertically onto
bulkheads in ships and permanently fixed inside containers
or onto wharves. KMT traps can easily be cleaned and
sterilised for bio-security purposes by boiling and are robust
enough to operate with minimum maintenance in estuarine
and marshland environments. They could be hoisted into
trees to sample for rodents in forest canopies or provide
protection to hole nesting birds, and are safe enough to be
set in many situations where use of other traps would pose
a risk to vulnerable non-target species.
In New Zealand, increasing numbers of community
groups vie for the same resources to set up predator control
programmes and many established projects are continually
expanding the areas already being trapped. Development
of effective long-life bait will be the key for using traps
instead of toxicants to control rats in mainland situations,
or for long term surveillance on islands. As trapping
technology and deployment improves, wider spacing and
less frequent servicing may make it possible to manage
larger areas for the same capital outlay, but care must be
taken to get the strategy right.
ACKNOWLEDGMENTS
Fig. 7 Waiaro trapping - comparative totals of rats caught
by period.
We are indebted to Bernard Goetz for engineering
advice and for fabricating the steel prototypes, to Jean
Fleming and Mary McEwen for the grant received from
the C.A. Fleming Trust and Alan Hall who made the “Weka
Bush” trial traps, but wouldn’t send a bill. Matt Maitland
and Dan Baigent organised the pilot trials with Department
of Conservation support and Manaaki Whenua Landcare
Research provided financial assistance for the independent
report. To Gideon Climo and Jörn Theuerkauf for sharing
valuable results from their trap trials in the tropics and
Katie Swift (USFWS), US Air Force and our Wake Atoll
237
Island invasives: eradication and management
survey colleagues for the opportunity to run the airfield
trapping grid. To Dion and Caren Paul (cofounders of
Ka Mate Traps Ltd) for the company name, logo and
generosity when moving on to bigger things and Fuka (Liu
Xuezheng “Allen” and Shi Cheng “Johnson”) for their
patience and producing a quality product. The Biodiversity
Condition Fund team provided advice and funding to
Waiaro Sanctuary, and to neighbours for their cooperation
and input into the project. To supportive friends such as
Ken Lipsmeyer, Ruth and Lance Shaw, Ron and Robynne
Peacock, Richard van den Berg and Richard Daem, Anna
Clark and numerous colleagues in science and conservation
circles who have provided help and encouragement over
many years, and more recently the Ka Mate trap users
who have provided feedback and useful suggestions. To
Keith Broome, John Innes and another reviewer who made
suggestions that improved the manuscript and Dave Towns
and Dick Veitch for editorial improvements. But not least
we acknowledge Pam and the long suffering Thomas
whanau for their vital role in the development of Ka Mate
Traps and this paper – arohanui ki a koutou katoa.
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