ORIGINAL PAPER Saved from extinction? Establishment and dispersal of Mercury Islands tusked weta, Motuweta isolata, following translocation onto mammal-free islands Ian Stringer • Corinne Watts • Danny Thornburrow • Rob Chappell • Robbie Price Received: 23 June 2013 / Accepted: 2 April 2014 / Published online: 13 April 2014 Ó Springer International Publishing Switzerland 2014 Abstract The Mercury Islands tusked weta, Motuweta isolata (Orthoptera: Anostostomatidae), survived only on 13 ha Ahu or Middle Island, a mammal-free island in the Mercury Group, New Zealand. Between 2000 and 2009, 567 individuals were translocated in nine releases to six nearby islands from which mammals had been removed. These translocations occurred to reduce the chance of accidental extinction of the Middle Island population of only a few hundred adults and to contribute to the resto- ration of the other islands. All translocated insects origi- nated from the captive-bred progeny of one male and two females collected from Middle Island between 1998 and 2001. Their establishment on Double and Red Mercury Islands, after their releases in 2000 and 2001 respectively, was confirmed by searching plots, and by using footprint tracking tunnels on Red Mercury Island between 2008 and 2012. Tracking tunnels provided better data and proved more cost effective than searching plots for detecting large tusked weta. Tracking tunnels demonstrated that the pop- ulation on Red Mercury expanded outwards from the release sites by 50–100 m each year between 2009 and 2012. These weta are now estimated to be present over more than half the Island. Tusked weta have also survived on Stanley, Korapuki and Ohinau Islands after releases in 2007, but they remain within 100 m of the release sites. No confirmed progeny of the weta released on Cuvier Island in 2008 and 2011 were detected. No tusked weta were detected on Middle Island using tracking tunnels on eight occasions between 2009 and 2012, suggesting this species is likely to be locally extinct. Despite possible failure on one island, these translocations have resulted in a signifi- cant conservation success outcome. Keywords Island conservation Á Monitoring Á Tracking tunnels Á Threatened taxa Introduction The Mercury Islands tusked weta, Motuweta isolata (Orthoptera: Anostostomatidae), is a large (46–73 mm adult body length), carnivorous, flightless, endemic Orthopteran. It was known only from Ahu or Middle Island (13 ha) in the Mercury Island Group, New Zealand. Mammals have never been present on this island. This weta is likely to have occurred on nearby islands and even the mainland before rats arrived in New Zealand because these islands were once joined to the mainland ca. 8,500 years ago when sea levels were lower (McIntyre 2001). It was apparent that M. isolata could become extinct through chance because of the small population size or by accident (e.g. if rats reached the island from a shipwreck) so this species was listed in the highest category for conservation action by Molloy and Davis (1992) and Molloy et al. (1994) and as Nationally Critical in subsequent threat listings of Hitchmough (2002) and Hitchmough et al. (2007). This resulted in the decision to captive-rear this weta and translocate it to other suitable mammal-free islands to establish multiple independent populations, thereby reducing the risk that this insect might become extinct, and to contribute to the restoration of the native biota of these islands, as proposed by Towns et al. (1990). I. Stringer Á R. Chappell Department of Conservation, PO BOX 10420, Wellington, New Zealand C. Watts (&) Á D. Thornburrow Á R. Price Landcare Research, Private Bag 3127, Hamilton, New Zealand e-mail: [email protected]123 J Insect Conserv (2014) 18:203–214 DOI 10.1007/s10841-014-9631-y
Transcript
ORIGINAL PAPER
Saved from extinction? Establishment and dispersal of MercuryIslands tusked weta, Motuweta isolata, following translocationonto mammal-free islands
Ian Stringer • Corinne Watts • Danny Thornburrow •
Rob Chappell • Robbie Price
Received: 23 June 2013 / Accepted: 2 April 2014 / Published online: 13 April 2014
� Springer International Publishing Switzerland 2014
Abstract The Mercury Islands tusked weta, Motuweta
isolata (Orthoptera: Anostostomatidae), survived only on
13 ha Ahu or Middle Island, a mammal-free island in the
Mercury Group, New Zealand. Between 2000 and 2009,
567 individuals were translocated in nine releases to six
nearby islands from which mammals had been removed.
These translocations occurred to reduce the chance of
accidental extinction of the Middle Island population of
only a few hundred adults and to contribute to the resto-
ration of the other islands. All translocated insects origi-
nated from the captive-bred progeny of one male and two
females collected from Middle Island between 1998 and
2001. Their establishment on Double and Red Mercury
Islands, after their releases in 2000 and 2001 respectively,
was confirmed by searching plots, and by using footprint
tracking tunnels on Red Mercury Island between 2008 and
2012. Tracking tunnels provided better data and proved
more cost effective than searching plots for detecting large
tusked weta. Tracking tunnels demonstrated that the pop-
ulation on Red Mercury expanded outwards from the
release sites by 50–100 m each year between 2009 and
2012. These weta are now estimated to be present over
more than half the Island. Tusked weta have also survived
on Stanley, Korapuki and Ohinau Islands after releases in
2007, but they remain within 100 m of the release sites. No
confirmed progeny of the weta released on Cuvier Island in
2008 and 2011 were detected. No tusked weta were
detected on Middle Island using tracking tunnels on eight
occasions between 2009 and 2012, suggesting this species
is likely to be locally extinct. Despite possible failure on
one island, these translocations have resulted in a signifi-
cant conservation success outcome.
Keywords Island conservation � Monitoring � Tracking
tunnels � Threatened taxa
Introduction
The Mercury Islands tusked weta, Motuweta isolata
(Orthoptera: Anostostomatidae), is a large (46–73 mm
adult body length), carnivorous, flightless, endemic
Orthopteran. It was known only from Ahu or Middle Island
(13 ha) in the Mercury Island Group, New Zealand.
Mammals have never been present on this island. This weta
is likely to have occurred on nearby islands and even the
mainland before rats arrived in New Zealand because these
islands were once joined to the mainland ca. 8,500 years
ago when sea levels were lower (McIntyre 2001). It was
apparent that M. isolata could become extinct through
chance because of the small population size or by accident
(e.g. if rats reached the island from a shipwreck) so this
species was listed in the highest category for conservation
action by Molloy and Davis (1992) and Molloy et al.
(1994) and as Nationally Critical in subsequent threat
listings of Hitchmough (2002) and Hitchmough et al.
(2007). This resulted in the decision to captive-rear this
weta and translocate it to other suitable mammal-free
islands to establish multiple independent populations,
thereby reducing the risk that this insect might become
extinct, and to contribute to the restoration of the native
biota of these islands, as proposed by Towns et al. (1990).
I. Stringer � R. Chappell
Department of Conservation, PO BOX 10420, Wellington,
New Zealand
C. Watts (&) � D. Thornburrow � R. Price
Landcare Research, Private Bag 3127, Hamilton, New Zealand
Traps, Warkworth, New Zealand). Once installed, the
tunnels were left in place and run by inserting pre-inked
tracking cards baited with ca 4 g of peanut butter. Weta
footprints on cards were measured with callipers after the
cards were collected to determine if they were from adult
or large juvenile H. isolata as described above. Differing
Fig. 1 Map of the Mercury Islands and Ohinau Island. Cuvier Island
(not shown) is 25 km north of Great Mercury Island
J Insect Conserv (2014) 18:203–214 205
123
numbers of tunnels were used on different islands but all
were centred on the release sites and extended for varying
distances from these; tunnels were positioned 30–100 m
apart using a GPS (estimated accuracy \4 m) (Table 2;
Figs. 3, 4, 5, 6). The sizes of release sites varied on each
island from ca 35 to 100 m2. On Red Mercury Island, a
4 9 3 grid of 12 tunnels 30 m apart was established near
the release site in 2009 and other tunnels were initially
spaced 50 m apart along three routes extending away from
the release site; after 350 m the spacing was increased to
100 m. On Korapuki Island a 4 9 4 grid was established
over the release site with other tunnels placed 50 m apart
extending from this over the island. The grids were used to
detect the initial spread of M. isolata from the immediate
release sites and to compare tracking tunnel results with
searching plots by scraping the soil. The tunnels on Stanley
Island and Ohinau Island were established in 2011 and all
were 30 m apart, while 10–12 tunnels were set at the
northern release site on Cuvier Island between 2008 and
2012, and three tunnels were set at the southern release site
on Cuvier in April 2012. Tunnels were also established
30 m apart on Middle Island in 2009, but the number used
on each subsequent occasion varied because some were
lost due to the activities of burrowing seabirds (Table 3).
Finally, tunnels were also set on Green Island in 2011 and
2012 to check if M. isolata was present there, but these
tunnels were removed after each use. All tunnels were run
for a minimum of 3 nights. The maximum time tunnels
were set depended on when sea conditions allowed access
to the islands (Table 2).
Searching plots
Plots were searched on Red Mercury Island, Korapuki
Island, Stanley Island, and Double Island. Searching
involved removing the leaf litter and scraping the top ca
5 mm of soil over an entire measured plot to reveal weta in
Table 2 Number of tracking tunnels (No. TT), number of nights the
tunnels (nights) were set for, presence of M. isolata (MITW) and the
percentage of tunnels tracked (%) on the translocated islands
Island Korapuki Red
Mercury
Stanley Ohinau Cuvier
North South
Date Location
Line Grid Line Grid RS RS RS RS
November-08
No. TT – – – – – – 10 –
Nights – – – – – – 4 –
MITW – – – – – – 0 –
% – – – – – – 0 –
March-09
No. TT 30 – 52 13 – – 10 –
Nights 15 – 16 16 – – 5 –
MITW 0 – 9 7 – – 0 –
% 0 – 17 44 – – 0 –
April-10
No. TT 30 16 – – – – 10 –
Nights 13 13 – – – – 35 –
MITW 0 0 – – – – 0 –
% 0 0 – – – – 0 –
March-11
No. TT 30 16 52 13 25 10 10 –
Nights 5 5 40 40 15 23 25 –
MITW 7 12 17 12 14 10 0 –
% 23 75 37 92 56 100 0 –
November-11
No. TT – – – – – – 10 –
Nights – – – – – – 6 –
MITW – – – – – – 0 –
% – – – – – – 0 –
February-12
No. TT 30 16 52 13 35 14 11 –
Nights 66 66 142 142 69 51 8 –
MITW 7 12 20 13 11 12 2 –
% 17 75 38 100 31 86 18 –
April-12
No. TT – – – – – – 11 6
Nights – – – – – – 8 8
MITW – – – – – – 1 1
% – – – – – – 0 33
Line—Tracking tunnels spaced along lines
RS—Tracking tunnels spaced along a line centred on the release site
Grid—Grid of tracking tunnels around the release site
%—Percentage of tracking tunnels with adult MITW footprints
Table 3 Number of tracking tunnels and number of night tunnels
were set to detect Motuweta isolata on Middle Island and Green
Island
Island Date No. TT Nights M. isolata %
Middle March 2009 20 16 0 0
Middle March 2011 12 8 0 0
Middle September 2011 34 89a 0 0
Middle December 2011 34 34a 0 0
Middle January 2012 36 24a 0 0
Middle February 2012 35 34a 0 0
Middle March 2012 35 22a 0 0
Middle April 2012 35 22a 0 0
Green December 2011 3 18 0 0
Green January 2012 3 23 0 0
Green February 2012 3 62 0 0
a Set continuously with new cards provided on these dates
206 J Insect Conserv (2014) 18:203–214
123
their underground burrows. When a weta was found, the
pronotum and metatibiae lengths were measured and
recorded to determine the life stage (Stringer et al. 2006).
Empty chambers were also recorded. All plots were
3 9 3 m2 except on Double Island, where they were
2.5 9 15 m2, with the total area searched on each island
varying from 54 to 288 m2. On Red Mercury and Korapuki
Island, each plot searched was associated with a tracking
tunnel on the grids at the release sites. The plots were
located randomly in relation to the tracking tunnels, with
most having their nearest edges between 1 and 5 m from
their corresponding tunnels, except on Korapuki Island in
2011, where half (16) of the plots were between 1 and 15 m
from their corresponding tunnels. Few plots were searched
on Stanley and Ohinau Islands because of time restraints,
so these were chosen to be [1 m from a tunnel to avoid
large boulders and trees (and water on Stanley Island)
while approximately evenly covering the release areas. The
large plots searched on Double Island were parallel to each
other and placed to cover the release area evenly.
Analysis
Maps were created in NZGD 2000 projection using ArcGIS
(ESRI 2011) and the coastlines were digitised at 1:5000
using WRAPS (2007) imagery. ArcGIS 10 was used to
map the tracking tunnel data (Position, presence or absence
of tusked weta). The Data Driven pages tool was used to
fine-tune map extents using an index layer, and these were
manually converted to bookmarks used to delimit the final
mapping extents.
Results
Distinguishing weta species from their footprints
Both adult and large juvenile M. isolata had significantly
larger protarsal, mesotarsal and metatarsal pad lengths than
any other weta species on the islands (Fig. 2). However,
footprints of small M. isolata were of similar size to those
of other weta present and could not be distinguished from
them by shape (Fig. 2). Footprints from tracking tunnels
used to measure dispersal were therefore recorded as M.
isolata (confirmed adult, or large juvenile: lengths of pro-
tarsus [3.7 mm, mesotarsus [4.7 mm and metatar-
sus [ 6.8 mm), probable M. isolata in locations where H.
thoracica was not known to be present (lengths of protarsus
3.4–3.7 mm, mesotarsaus 4.1–4.7 mm and metatarsus
5.6–6.8 mm) or ‘other weta’ (lengths of protarsus
\3.4 mm, mesotarsus\4.1 mm and metatarsus\5.6 mm).
Tarsal pads were longer than the lengths of their prints on
all cards for all weta tracked (n = 55), regardless of
species, sex or age class and only 56 % (±1 %), 64 %
(±3 %), and 83 % (±5 %) of the actual length of the
protarsal, mesotarsal and metatarsal pads, respectively,
were recorded on cards.
Motuweta isolata dispersal
On Red Mercury Island, tusked weta were found up to
150–200 m from their two release sites 8–9 years after
their liberation. Their footprints were in 44 % of the
tracking tunnels within the release site grid and 17 % of the
tunnels spaced over the island and away from the grid. The
weta continued to disperse outward ca. 50–100 m per year:
in 2012 footprints were found in 100 % of the tunnels in
the grid and 38 % of the tunnels across the Island. In
addition, tusked weta prints were recorded in one tunnel at
the north of the island and single tunnels in the northwest
of the island had probable tusked weta prints in both 2011
and 2012 (Table 2; Fig. 3). No tunnels were set in 2010
because rough seas prevented us from landing on the
island.
On Korapuki Island, no confirmed tusked weta were
detected when tunnels were first used in 2009; however, in
2010 two tunnels on the grid and two near the grid had
possible tusked weta footprints, although these footprints
could have been from large tree weta. Sixteen tunnels had
tusked weta footprints in 2011 and the number tracked
subsequently increased to 63 % of tunnels on the grid and
17 % of those near the grid in 2012. However, all evidence
of tusked weta was restricted to within \250 m of the
release site, except for possible footprints in one tunnel
located in the north of the island in 2012 (Table 2; Fig. 4).
Actual length of tarsal pad (mm)
2 4 6 8 10 12 14 16 18
Ave
rage
leng
th o
f tar
sal p
ad p
rinte
d on
car
d (m
m)
2
3
4
5
6
7
8
9
10
Adult Motuweta isolataSubadult M. isolataJuvenile M. isolataAdult Hemideina thoraciaSubadult H. thoraciaJuvenile H. thoraciaAdult Hemiandrus pallitarsis
Fig. 2 Relationship between length of tarsal pad and average length
of tarsal pad print on a footprint tracking tunnel card. Adult and last
instar juvenile M. isolata prints were significantly larger than all other
adult weta species measured. Bars show 95 % confidence intervals.
Note that only results for the metatarsal pad are presented; data
showed similar differences for protarsal and mesotarsal pads
J Insect Conserv (2014) 18:203–214 207
123
Tracking rates of M. isolata in tunnels on Ohinau and
Stanley Islands showed they were present at each of the
release sites in 2011 and 2012 (Figs. 5, 6). On Stanley
Island, all tunnels set at the southern release site in 2011
were tracked and a similar area was tracked again in 2012
after additional tunnels were added to the northwest and
south (Table 2; Fig. 6). This indicated that the weta had
dispersed only 60 m from this release site. At the northern
site, tusked weta have remained within 30 m of where they
were released (Table 2; Fig. 6). On Ohinau Island, tusked
weta footprints were found in all tunnels set in 2011,
indicating they had moved at least 60 m from their release
site and after additional tunnels were set in 2012, they were
found at least 100 m from their release site (Table 2;
Fig. 5).
No tusked weta were detected in tunnels at the northern
release site on Cuvier Island in 2009, 2010, 2011 or in
April 2012, but they were detected in 14 % of tunnels set in
March 2012. No tusked weta were detected at the southern
release site on Cuvier Island in February 2012 but their
footprints were present in one tunnel there in April 2012
(Table 2). No M. isolata were detected in tunnels on
Fig. 3 Presence of M. isolata on Korapuki Island. Circles tracking
tunnels at release sites and extending across the island; squares
30 9 30 m grid of tracking tunnels centred on the release site on
Korapuki and Red Mercury Islands. Closed symbols presence of adult
and subadult tusked weta; dark grey symbols probable M. isolata; and
open symbols no tusked weta tracked. Open stars indicate the location
of a release site
208 J Insect Conserv (2014) 18:203–214
123
Middle Island set between March 2009 and February 2012,
or in tunnels set on Green Island in 2012 (Table 3).
Searching plots
A total of 54 M. isolata were found during plot searches on
the islands (Table 4). The highest density (0.413 weta per
m2) was found at the release site on Double Island, whereas
densities on the other islands varied from no weta (Korapuki
Island, 2009) to 0.068 weta per m2 (Red Mercury Island,
2009). All plots searched on Ohinau Island were within the
release area, whereas those on Red Mercury, Korapuki and
Stanley Islands, while including the release areas, extended
up to 100 m away from them (Table 4; Figs. 3, 4, 5).
Night searches
No tusked weta were seen on Cuvier Island when the
northern release area was searched during the nights of
16–19 October 2008, 24 February 2010, and 30 May 2011,
and none were seen on Middle Island when it was searched
on the night of 2 April 2008.
Comparison of searching plots and using footprint
tracking tunnels for detecting tusked weta
Adult and subadult M. isolata were detected in more
locations using tracking tunnels than by searching plots on
Red Mercury Island and Korapuki Island (Table 4). The
Fig. 4 Presence of M. isolata on Red Mercury Island. Symbols as in Fig. 3
J Insect Conserv (2014) 18:203–214 209
123
percentage of the grid where tusked weta were detected
using tracking tunnels increased on both islands from 2009
to 2011, whereas searching plots produced variable results
(Table 4). There appeared to be no relationship between
the percentage of the grid where M. isolata were detected
by searching plots and that detected by using tracking
tunnels (Table 4).
Discussion
Establishment and dispersal of M. isolata following trans-
location onto mammal-free islands
Footprint tracking tunnels have revealed that M. isolata
is now well established on Red Mercury Island, where
these weta are expanding their range at a rate of
Fig. 5 Presence of M. isolata on Ohinau Island. Circles tracking tunnels at and extending away from the release site. Closed symbols presence of
adult and subadult tusked weta; dark grey symbols probable tusked weta; and open symbols no tusked weta tracked
Fig. 6 Presence of M. isolata on Stanley Island. Symbols as in Fig. 5
210 J Insect Conserv (2014) 18:203–214
123
100–150 m per year. Our results from searching plots also
indicate that the weta are abundant at the release site on
Double Island. The lifespan of M. isolata is estimated to be
1.7–3.2 years or longer (Stringer et al. 2006) so they have
now passed through about 3–7 generations on these two
islands. Footprint tracking tunnels have also shown that
these weta have survived on Korapuki, Stanley, and Oh-
inau Islands, but as their ranges have not expanded except
at the southern release site on Stanley Island and they have
only completed one or two generations we do not yet know
if they are likely to establish there. In contrast, the small
range expansions that have occurred at the southern release
site on Stanley Island and on Ohinau Island suggest that
they might become established there. We do not know if
tusked weta have survived on Cuvier Island despite tusked
weta footprints being found there in 2012. This is because
the tunnels on Cuvier were set following the second
release and the footprints recorded could have come from
second release insects that had matured rather than from
progeny of the first release (Table 2). Certainly, no tusked
weta footprints were found on Cuvier Island when tunnels
were set before the second release, suggesting that the
insects had either not survived, or had moved away from
the release site. It was for this reason that a second
translocation was made with some weta being released
again at the first (northern) site and others being released in
a second site alongside a small stream near buildings
(southern site) (Table 1).
Our results show that little or no dispersal was detected
during the years immediately following the releases on
Stanley and Ohinau Islands and that although some dis-
persal occurred initially on Korapuki Island, this was
limited and no substantial dispersal has occurred subse-
quently. This suggests the majority of both the released
insects and their offspring remained within 30–60 m of the
release sites. We suggest that if such behaviour also
occurred on Double and Red Mercury Islands this may
have contributed to their successful establishment because
they may have been less likely to find mates if they had
dispersed. We speculate that this may be the usual pattern
and that they disperse more widely only after their num-
bers have increased at the release sites. Further monitoring
using tracking tunnels is required to confirm whether the
same pattern of movement occurs on Stanley, Korapuki
and Ohinau Islands, but it seems likely to have happened
on Red Mercury Island because tusked weta had only
dispersed up to 180 metres from their release points after 8
or 9 years. We note that the occasional tusked weta dis-
perses more widely than most of the others, as evidenced
by finding their footprints in at least one location at the
northern end of Red Mercury Island, some hundreds of
metres (a minimum of 600 m) from locations where other
tusked weta were detected. Little is known about how farTa
ble
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J Insect Conserv (2014) 18:203–214 211
123
individual M. isolata move. McIntyre (2001) reported that
on Middle Island although most weta, including juveniles,
were found in three small areas totalling ca. 0.2 ha prob-
ably because the habitat there was the most suitable, males,
‘‘ranged widely … while females seemed to use one or a
few burrows within an area extending perhaps 10–20 m’’ in
May and June. Adults can potentially move large distances
because eight fitted with radio transmitters moved in total
up to 32 m from where they were first found when fol-
lowed for up to 8 days on Middle Island (M. McIntyre,
unpublished data) and four others with radio transmitters
moved up to 14.8 m over 3 nights after they were released
on Red Mercury Island (Stringer and Chappell 2008).
What technique should be used for monitoring M.
isolata?
Stringer and Chappell (2008) tested a number of techniques
for monitoring M. isolata and found that searching plots by
scraping the top 5 mm of leaf litter and soil to reveal weta
in their underground burrows allowed them to follow the
progress of weta after initial releases on Double and Red
Mercury Islands. This, however, was before Watts et al.
(2008) began testing footprint tracking tunnels, with the
result that tunnels are now commonly used for monitoring
giant and tree weta in New Zealand (Watts et al. 2008,
2011a, b). Both plot searching and tracking tunnels have
advantages and disadvantages (Table 5). Searching plots
by scraping was an effective method of finding M. isolata
when they were at high densities and had not dispersed far
from their release sites. This technique has the advantage
of providing an absolute density estimate and, as any weta
found can be collected, other information such as mea-
surements can also be obtained or antennal samples taken
for DNA analysis. The disadvantages are that the technique
is time-consuming (ca. 66 min per person to walk 30 m
and search a 9 m2 plot; Table 5) because this affects the
area that can be searched and the number of replicates that
can be taken when time is limited; the technique also
causes significant disturbance to the top ca. 1 cm of soil
and leaf litter layer.
Tracking tunnels, on the other hand, showed that
tusked weta were present even when no weta were found
by searching plots. Tunnels also enabled us to demon-
strate that M. isolata have survived for several genera-
tions on all the islands where they were released, with
the possible exception of Curvier Island. Tunnels also
allowed us to monitor the dispersal of weta from release
sites. Detection of tusked weta using tracking tunnels
was less variable between monitoring years than detec-
tion by searching plots; tunnels were relatively time
efficient (ca. 11.3 min per person per tracking tunnel set
30 m apart; Table 5), and allowed us to detect whether
tusked weta were present up to 1.2 km from their release
areas The disadvantages of tracking tunnels are that only
footprints are recorded so information such as sex or
instar number cannot be obtained, and only the largest
weta present in an area can be unambiguously identified
to species from the size of their footprints. Apart from
size, the footprints of weta species cannot be distin-
guished from one other. Thus tracking tunnels are an
effective monitoring tool for detecting if a large threa-
tened species, such as M. isolata, is present. Once
detected, other search methods such as searching plots or
spotlighting at night would have to be used to locate
individual specimens if these were required.
Is M. isolata extinct on Middle Island?
No footprints of M. isolata were found in any of the
tracking tunnels set on Middle Island, even while tusked
weta were detected in tunnels set at the same time on
nearby islands, such as Stanley Island (1.9 km away) and
Korapuki Island (2.1 km away), where there were trans-
located populations. In addition, between March 2009 and
February 2012, tracking tunnels were set on eight sampling
occasions on Middle Island and no weta were detected.
This project suggests that tracking tunnels provide a rela-
tively sensitive method for detecting whether tusked weta
are present and our results therefore provide further evi-
dence that this species may now be locally extinct on
Middle Island as suggested by Stringer and Chappell
(2008). This probable extinction occurred on Middle Island
which is mammal-free so what are the chances of it
Table 5 Comparison of using tracking tunnels and searching plots for detecting Motuweta isolata on Korapuki Island
Monitoring technique used to
detect
M. isolata in the Korapuki grid,
2011
Minutes taken to set
out in the field
Minutes taken to
collect field data
Total time
involved
Ease of
technique
Degree of disturbance of
technique to habitat
Specimen
obtained
Scrape searches (3 9 3 m plots)
at 16 tracking tunnel sites
0 350 350 Difficult High Yes
Weta footprints in 16 tracking
tunnels
150 30 ? (15 lab
analysis)
195 Easy None No
Plots were searched by scraping the soil surface to reveal weta in underground chambers. Times are for three people to search 16 plots together
and for each person to set and check four tracking tunnels
212 J Insect Conserv (2014) 18:203–214
123
becoming extinct on the islands where it was released? We
do not know why this weta became extinct on Middle
Island but the probable reasons are less likely to apply to all
of the translocation islands. It is likely that the possible
extinction on Middle Island followed after numbers were
reduced during a severe drought in 1993–1994 (Stringer
and Chappell 2008). Prior to this only low numbers of M.
isolata were once present so extinction could have been a
stochastic event. Most of the weta also occurred in local-
ized areas that retained moisture during dry periods of
summer and autumn (McIntyre 2001) so a reduction in the
population during the severe drought of 1993–1994 would
have increased the chance of an extinction occurring. In
contrast, these weta are now present in an area extending
up to 33 ha on Red Mercury Island suggesting that the
population is much larger than it was on Middle Island.
Furthermore, some of these weta live alongside a perma-
nent stream. A permanent stream is also present on Cuvier
Islands and the southern release site on Stanley Island is
adjacent to a large temporary pond that forms during
autumn where the soil always appears moist so it is more
likely that they could survive better on both these islands
than on Middle Island during severe droughts. It is more
likely that prolonged drought might cause extinction on
Double, Korapuki and Ohinau Islands although these island
are more than 2.5 times the area of Middle Island and the
release sites are in areas of moist soil situated in valley
floors or, in the case of Double Island on an extensive ledge
and all drain much larger catchments than the sites where
these weta live on Middle Island.
Recommendations and conclusions
The objective of all these translocations was to establish
self-sustaining populations of M. isolata on other islands to
both reduce the chance of its extinction and to be part of
the restoration of these islands. Our study has confirmed
that this has been achieved at least for Red Mercury and
Double Islands. However, all weta released are progeny of
only one male and two females, so inbreeding depression is
likely although it is probable that this species already had
low genetic variability due to the small population present
on Middle Island (McIntyre 2001), and because repeated
droughts would have caused reduction in weta numbers
(Stringer and Chappell 2008).
Tracking tunnels are clearly the best method so far
devised for detecting the presence of adult and large
juvenile M. isolata. They have proved ideal for monitoring
the establishment of this species after translocation and, as
far as we are aware, tracking tunnels have allowed us to
follow how they dispersed from their release sites in finer
detail than has been done for previous conservation related
translocations of insects, with the exception of Hochkirch
et al. (2007) who followed the expansion of a re-introduced
population of Gryllus campestris (Orthoptera: Gryllidae)
by locating stridulating males.
If, as now seems probable, M. isolata is locally extinct
on Middle Island, where it originally survived, then these
translocations have saved a threatened insect species from
extinction. This is a significantly important conservation
success story comparable with that of the New Zealand
black robin (Butler and Merton 1992). Several factors,
together with a lot of good luck, were responsible for this
success. First, Winks and Ramsay (1998) rapidly devel-
oped an effective captive-rearing method that was then
used to produce 130 weta for experimental translocations
(Winks et al. 2002). As the latter captive breeding was
done to test the translocation method, only three females
and one male were collected from Middle Island between
1998 and 2001. These four insects happened to be among
the last six tusked weta seen on Middle Island: none have
subsequently been detected there either by searching at
night or by using tracking tunnels. There was, however, a
problem with the fertility of these insects: most of the eggs
were laid by one female, another female produced only a
few eggs, and the third female was infertile. Luckily, the
only male was fertile. Furthermore, the first generation of
captive-bred tusked weta had low fertility when kept in
captivity, which resulted in few second-generation insects.
Thus, all the tusked weta used for translocations originated
from a single male and from two females (Winks et al.
2002; Stringer and Chappell 2008). The only other docu-
mented cases of insects being reared for successful trans-
location from a low number of founders are among
butterflies, where just 3–5 females were sufficient to
establish some new colonies (Oates and Warren 1990). The
Marsh fritillary butterfly (Euphydryas aurinia), an endan-
gered species in most of northern Europe, is a good
example because it is now more widespread in reintro-
duced localities than in its original, natural ones (Schultz
et al. 2008). In our case we were fortunate, because the
experimental translocations of tusked weta both to Double
Island and to Red Mercury Island were successful, given
that initial attempts to translocate insects can fail (e.g. New
2012); and also given that the second generation of captive-
bred weta retained for further breeding were infertile (C.
Winks, unpublished results). Subsequently, tusked weta on
Double Island and Red Mercury Island became sufficiently
abundant to allow individuals to be collected for further
captive-breeding and subsequent release, and for one direct
transfer from Double Island to Cuvier Island. Finally, the
timely development of tracking tunnels for monitoring
large weta allowed us to follow in relatively fine detail the
initial establishment and dispersal of tusked weta on the
islands where they were released.
J Insect Conserv (2014) 18:203–214 213
123
Acknowledgments This research was supported by Core funding
for Crown Research Institutes from the Ministry of Business, Inno-
vation and Employment’s Science and Innovation Group under
CO9X0503 and DOC investigation No. 3124. Thank you to Lesley
McKay, David Ruscoe, Esta Chappell, and Craig Briggs who assisted
with fieldwork. Sincere thanks to Chris Winks for footprinting and
measuring the feet of captive tusked weta. John Innes, Bill Lee, Don
Newman, and Anne Austin provided useful comments on manuscript.
References
Butler D, Merton D (1992) The black robin: saving the world’s most
endangered bird. Oxford University Press, Auckland
Chappell R (2008) Final report: operational plan for eradication of
ship rats (Rattus rattus), kiore (Rattus exulans), house mouse
(Mus musculus) and rabbit (Oryctolagus cuniculus cuniculus)
from Ohinau and Motutapere Islands. Department of Conserva-
tion, Hamilton
ESRI—Environmental Systems Resource Institute (2011) ArcGIS
Desktop: Release 10. ESRI, Redlands, California, USA
Gibb JG (1986) A New Zealand Holocene eustatic sea level curve and
its application to vertical tectonic movements. In: Reilly WI,
Hartford BE (eds) Recent crustal movements of the Pacific
region. Royal Society of New Zealand Bulletin No. 24, Royal
Society of New Zealand, Wellington
Gibbs GW (1990) Report on a visit to Middle Island, Mercury Group,
to survey ‘tusked’ wetas, October 1989. Department of Conser-
vation, Wellington
Green CJ (2005) Using artificial refuges to translocate and establish
Auckland tree weta Hemideina thoracica on Korapuki Island,
New Zealand. Conserv Evid 2:94–95
Hitchmough RA (2002) New Zealand threat classification system lists
2002. Threatened species occasional publication No 23. Depart-
ment of Conservation, Wellington
Hitchmough RA, Bull L, Cromarty P (2007) New Zealand threat
classification system lists 2005. Department of Conservation,
Wellington
Hochkirch A, Witzenberger KA, Teerjling A, Niemeyer F (2007)
Translocation of an endangered insect species, the field cricket
(Gryllus campestris Linnaeus, 1758) in northern Germany.
Biodivers Conserv 16:3597–3607
McIntyre M (2001) The ecology of some large weta species in New
Zealand. In: Field LH (ed) The biology of weta, king crickets
and their allies. CABI publishing, Wallingford
Meads M (1994) Unpublished letter to Rob McColl 26/11/94, file No.
INS-006. Department of Conservation, Wellington
Moeed A, Meads MJ (1987) Invertebrate survey of offshore island in
relation to potential food sources for the little spotted kiwi,
Apteryx oweni (Aves: Apterygidae). N Z Entomol 10:50–64
Molloy J, Davis A (1992) Setting priorities for the conservation of
New Zealand’s threatened plants and animals. Department of
Conservation, Wellington
Molloy J, Davis A, Tisdall C (1994) Setting priorities for the
conservation of New Zealand’s threatened plants and animals,
2nd edn. Department of Conservation, Wellington
New TR (2012) Insect conservation: past, present and prospects.
Springer, London
Oates MR, Warren MS (1990) A review of butterfly introductions in
Britain and Ireland. Report for the Joint Committee for the
conservation of British insects founded by the World Wide Fund
for Nature
Schultz CB, Russell C, Wynn L (2008) Restoration, reintroduction
and captive propagation for at-risk butterflies: a review of British
and American conservation efforts. Isr J Ecol Evol 54:41–61
Stringer IAN, Chappell R (2008) Possible rescue from extinction:
transfer of a rare new Zealand tusked weta to islands in the
Mercury Group. J Insect Conserv 12:177–188
Stringer IAN, Mack H, Grant EA, Winks CJ (2006) Growth and
development of captive reared Mercury island tusked weta,
Motuweta isolata Johns (Orthoptera: Anostostomatidae). N Z
Entomol 29:5–19
Thompson P (1992) Proposal to transfer MITW to captivity.
Unpublished report, file No. INS-006. Department of Conserva-
tion, Wellington
Towns DR, Atkinson IAE (2004) Restoration plan for Korapuki
Island (Mercury Islands), New Zealand 2004–2014. Department
of Conservation, Wellington
Towns DR, Broome KG (2003) From small Maria to massive
Campbell: forty years of rat eradications from New Zealand
