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 Faculty of Science School of Animal Biology The University of Western Australia Bunbury Outer Ring Road: monitoring arboreal mammals during road construction Interim Progress Report 1, 2012 By Roberta Bencini and Brian Chambers School of Animal Biology The University of Western Australia Executive Summary This report details the results of work conducted by staff and students from The
University of Western Australia immediately before and during the construction of the
Bunbury Outer Ring Road Stage 1 with funds provided mainly by Main Roads Western
Australia.
The aim of the project was to assess three mitigation measures to minimise the impact
of the road construction on wildlife:
1. use of a ‘relocation’ strategy;
2. installation of a rope bridge; and
3. installation of a fauna underpass.
Here we report on results obtained while investigating mitigation measure 1 or the use
of a relocation strategy. Experimental relocations were conducted in an attempt to minimise
the impacts of road construction on the populations of arboreal marsupials found in the area,
with emphasis on protecting the western ringtail possum (Pseudocheirus occidentalis). We
additionally studied the other two arboreal marsupials found in the area: the common
brushtail possum (Trichosurus vulpecula hypoleucus) and the brush-tailed phascogale
(Phascogale tapoatafa).
In March and April 2012, when the road construction works began, we searched
intensively the area affected by and adjacent to the road alignment for western ringtail
possums using spotlights. This resulted in the capture of eight western ringtail possums that
were fitted with radio transmitter collars that transmitted at a different frequency if an animal
did not move for more than 3-4 hours. This allowed us to detect any dead animals, retrieve
the carcasses, and investigate the causes of death.
Three western ringtail possums were found directly on the road alignment and so were
relocated to a nearby release site because they were directly at risk from the road construction
operations. Two additional western ringtail possums were found on the vegetation the night
after it had been pushed over for clearing and were also captured and relocated. Another
three western ringtail possums were found near the road alignment and were fitted with radio
transmitters and then released at their point of capture.
We also trapped the area intensively with 434 trap nights to catch any fauna directly
present on the road alignment. This resulted in the capture of only one additional marsupial,
a male brush-tailed phascogale that was fitted with a radio collar and released. The collar,
however, was found on the ground the day after its release.
Fauna was also captured using the same methods at a reference site located
approximately 0.5km north of the road alignment to study the survivorship of fauna that were
not directly affected by the road construction operations. This 100ha area was purchased by
Main Roads WA as an offset and consisted of bushland where we captured and radio collared
six western ringtail possums, eight common brushtail possums and five brush-tailed
phascogales.
Three out of five relocated western ringtail possums died within few weeks from their
release, two from possible fox predation as established by DNA swabs of the retrieved
collars. This is termed possible fox predation because the presence of fox DNA on their
collars does not exclude that they might have been scavenged on after they died from other
2 causes. The other translocated possum possibly died because its collar became stuck in a tree
branch, however the body could not be retrieved and an autopsy could not be conducted. No
other western ringtail possums died during the study at either the reference site or the site
next to the road alignment.
Only one male common brushtail possum died from presumed fox predation at the
reference site, while all the other animals survived until the end of the study.
Five brush-tailed phascogales were radio tracked at the reference site but due to size
limitations the collars did not have a mortality switch, so often it was unclear if animals were
dead up in a tree of if they had managed to remove their collars, which we observed they
were capable of doing throughout the study. Only two of the brush-tailed phascogales were
confirmed dead, one from possible fox predation and the other due to the male die-off, a
phenomenon exhibited in this species where all males die after the mating season.
The results of this work support the notion that survival of relocated western ringtail
possums is low, especially in the presence of introduced predators. Significantly, all of the
non-relocated possums living next to the road alignment were still alive at the end of the
study despite the disturbance going on around them.
As our work has shown that western ringtail possums can survive when the vegetation
is pushed over for clearing, searching of this vegetation by experienced personnel should be
conducted in the nights after the vegetation has been pushed over to capture and relocate any
surviving possums. Mulching of this vegetation should be conducted as late as possible to
give time for any surviving animals to move away of their own accord in case they are not
found and relocated.
In the future it would be advisable to survey proposed road construction sites well in
advance to determine the home range of western ringtail possums before the clearing begins
and establish if there is suitable area of the original range that would remain intact after the
clearing. In this case the animals could be held temporarily while the vegetation is cleared
and released in what remains of their range after clearing, thus avoiding the risks associated
with relocating them.
Further studies during road construction events and with greater number of animals
should be undertaken to clarify if the survivorship of relocated ringtail possums will improve
if fox control operations are in place and if additional measures such as the provision of nest
boxes are implemented.
3 Acknowledgments We gratefully acknowledge the financial support of Main Roads Western Australia for
the funding to conduct this work, for their commitment to the environment and particularly
Alan Grist for practical help throughout the project and Gerry Zoetelief for his unreserved
support.
We also wish to thank:
Jessica Hunter and her volunteers for radio tracking the animals throughout the study;
Kaori Yokochi for help with trapping, darting and statistical analyses;
Jacob Cumberworth, Fulton Hogan’s Environmental and Safety Officer, for help with
radio tracking and trapping;
Steven Correia for help with trapping at the start of the study;
Greg Harewood for help during trapping and capture of western ringtail possums.
4 Contents Executive Summary ........................................................................................... 2
Acknowledgments............................................................................................. 4
Background ....................................................................................................... 6
Introduction ...................................................................................................... 6
Methodology..................................................................................................... 7
Study species.............................................................................................................................................7
Study area..................................................................................................................................................8
Capture of animals....................................................................................................................................8
Monitoring of animals ............................................................................................................................10
Statistical analyses ..................................................................................................................................11
Results............................................................................................................. 11
Discussion ....................................................................................................... 14
Management Recommendations .................................................................... 16
References ...................................................................................................... 18
Appendix 1 ...................................................................................................... 21
5 Background The Australian Commonwealth Department of Sustainability, Environment, Water,
Population and Communities granted approval to Main Roads Western Australia (MRWA) to
construct the Bunbury Port Access Road Stage 2 and the associated road linkages including
the Bunbury Outer Ring Road Stage 1 (BORR Stage 1). The construction of the BORR
Stage 1 required clearing of up to 5.5 ha of confirmed and 14.3 ha of potential western
ringtail possum (Pseudocheirus occidentalis) habitat and its approval was subject to eleven
conditions (McCarthy 2011). Condition 7 required MRWA to prepare a management plan to
identify the mitigation measures to be adopted to reduce the impacts of the road construction
on the threatened western ringtail possum. This was completed in October 2011 (McCarthy
2011) and included the involvement of staff and students from The University of Western
Australia to conduct the necessary research on the proposed mitigation measures.
Introduction Roads are known to have a negative impact on the environment due to habitat loss and
fragmentation, edge effects, barriers to movement, invasion of undesirable flora, fauna and
disease, vehicle collisions and environmental pollution (Keller et al. 2004; Goosem 2007;
Fahrig & Rytwinsk 2009; Soanes & van der Ree 2009). These effects, in particular barrier
effects and road mortality, can be devastating for arboreal mammals that depend on trees for
their survival (Goosem et al. 2005).
Populations of obligate arboreal species suffer almost complete isolation of fragmented
populations as a result of the construction of roads and development of other infrastructure
(Jones et al. 1994a, Wilson et al. 2007). Facultative arboreal species can also be severely
affected as they are at risk from both predators and vehicles when they attempt to cross roads
on the ground (Dique et al. 2003).
One such species is the western ringtail possum, which is endemic of the southwest of
Western Australia, the only biodiversity hotspot on mainland Australia (Myers et al. 2000),
and is especially susceptible to the clearing necessary to build roads and other infrastructure
because they are strictly arboreal, have small home ranges and have a limited geographic
range, which is subject to rapid development (de Tores et al. 2004; Clarke 2011).
To manage them during developments western ringtail possums are generally
translocated, often to inappropriate areas, without adequate research to determine whether
this is the best course of action (A. Wayne pers. comm.). For example, at the Leschenault
Peninsula many translocations have been attempted but after initial successes, these
populations crashed and the cause is still unknown (McCutcheon et al. 2007).
While generally used for the conservation of threatened or endangered species,
translocations are used increasingly to resolve human-animal conflicts such as that generated
by the development of roads (Lindenmayer & Burgman 2005) but very few studies so far
have investigated the benefits of moving these animals away compared with keeping them in
their original areas of occupation (Griffith et al. 1989; Cowan 2001; Eymann et al. 2006;
Roselan 2009; Clarke 2011).
Roselan (2009) conducted the only study so far that examined the survival rates of
common brushtail possums that were left within their home range during the clearing for the
6 construction of the Mandurah Entrance Road, now named Mandjoogoordap Drive, in
Western Australia. She found that all brushtail possums were still alive at the end of the fivemonth study in contrast with Pietsch (1994) who found that only two out of ten translocated
common brushtail possums survived for more than ten weeks. However, in Roselan’s (2009)
study none of the animals were actually moved away from the area for comparison with those
managed in situ. Additionally, no similar study has been conducted on the western ringtail
possum during the clearing for the construction of a road.
The construction of Bunbury Outer Ring Road Stage 1 provided the opportunity to
conduct research to study the effects of the road construction on the arboreal mammals found
in the area. Extensive searches and trapping revealed that three arboreal species were present
in the area: the western ringtail possum, the common brushtail possum and the brush-tailed
phascogale (Phascogale tapoatafa), which are all within the Critical Weight Range defined
by Burbidge & McKenzie (1989) as the weight range of mammals that have suffered severe
declines after European settlement, mainly due to introduced predators and habitat
destruction. As these are arboreal species that spend most of their lives in trees, they can be
severely affected by the loss of these trees or the loss in continuity of the canopy (Laurance &
Laurance 1996).
The management plan included the removal and relocation of animals found directly on
the road alignment to undisturbed vegetation within the study area (McCarthy 2011). At the
same time an area of bushland purchased by Main Roads WA 0.5km north of the road
alignment provided an opportunity to compare the survival of animals that were translocated
or retained on site in remaining habitat near the road alignment with those in an area not
directly impacted by the road construction.
We hypothesised that animals that had to be moved away from the clearing site would
have a lower survival rates than those that were kept within their home ranges, both within
the road construction area and at the reference site where animals were left completely
undisturbed.
Methodology To test this hypothesis we studied the survivorship of fauna relocated from the road
alignment to adjacent vegetation and compared it with that of fauna left within their home
ranges next to the road alignment and of fauna living undisturbed in the reference site. Study species The three study species are arboreal and spend most of their lives in trees. They are
nocturnal, foraging in the canopy at night and resting during the day.
The western ringtail possum is classified as ‘vulnerable’ under the Environment
Protection and Biodiversity Act 1999 and the IUCN (IUCN 2012), and ‘rare or likely to
become extinct’ under the Wildlife Conservation Act 1950. Averaging between 820 and
1020g for both sexes, the western ringtail possum is a folivore that is able to construct its
own nest, called a ‘drey’, composed of twigs and leaves from surrounding vegetation, so it
does not rely solely on tree hollows for nesting (Jones et al. 2004). They rarely descend from
the trees where they live to travel along the ground, and are therefore threatened by habitat
destruction and fragmentation (Jones et al. 1994b; Clarke 2011). They occur in patchy
distributions in the south west of Western Australia, in areas dominated by peppermint trees
7 (Agonis flexuosa). This patchy distribution and specific habitat means that all populations of
western ringtail possums are important for the conservation of this species (Clarke 2011).
Although the common brushtail possum is classified as ‘least concern’ by the IUCN
(IUCN 2012) the subspecies T. V. hypoleucus found in the southwest of Western Australia is
in decline (Wayne et al. 2005). Once it was widespread throughout the whole of Western
Australia, but it is now restricted to the southwest of Western Australia (Bennett et al. 1991).
Unlike the western ringtail possum it is more willing to move along the ground and it is more
omnivorous in its diet. This species nests in tree hollows or rabbit burrows when no other
nesting sites are available (Wayne et al. 2005).
The brush-tailed phascogale is classified as near threatened (IUCN 2012), and is
vulnerable to similar threats as the western ringtail possum and the brushtail possum (Rhind
& Bradley 2002). A small (110g and 150g for females and males respectively), carnivorous
dasyurid, the brush-tailed phascogale is highly threatened in many areas of the south west and
little researched, so its conservation is important (Soderquist 1995; Rhind & Bradley 2002).
Nesting exclusively in tree hollows, and feeding primarily on invertebrates found underneath
the bark of trees, the brush-tailed phascogale is highly vulnerable to habitat loss and
fragmentation, particularly of those trees bearing tree hollows (Rhind 1996; Scarff et al.
1998; van der Ree et al. 2001; van der Ree et al. 2006). Like other small dasyurids, it
displays the phenomenon of the male die off, in which all males die shortly after the mating
season (Soderquist 1995).
Study area The study area comprised the vegetated and partially cleared land abutting each side of
the BORR Stage 1. Construction of this road severed a contiguous section of eucalypt
woodland that included tuart (Eucalyptus gomphocephala), marri (Corymbia calophylla) and
jarrah (Eucalyptus marginata) as the main overstorey species, with groves of sheoak
(Allocausarina fraseriana), paperbark (Melaleuca rhaphiophylla), banksia (Banksia spp.) and
peppermint known to contain western ringtail possums (McCarthy 2011).
The study area encompassed a range of land uses, tenure and vesting. Much of this
area was proposed to be vested as secure conservation estate and comprised a 100ha block of
bushland located some 500m north of the proposed alignment, which was purchased as an
offset by MRWA. Within the study area we selected three different sites: a release site where
animals were relocated if found directly on the road alignment, a treatment site, which was
the vegetation immediately adjacent to the road alignment and a representative reference site,
located in the offset bushland north of the alignment (Figure 1; Hunter 2012). The release
site was chosen due to the presence of peppermint and other tree species with good canopy
connections that would provide food, shelter and nesting materials for western ringtail
possums.
Capture of animals At the start of the study, the road alignment and the reference site were trapped using
wire cage traps (220x220x450mm, Sheffield Wire Products, Welshpool WA) baited with
universal bait (a mixture of peanut butter, rolled oats and sardines) and pieces of apple to
capture small and medium size mammals. The same areas were intensively surveyed through
spotlight searching to locate and catch western ringtail possums. To capture western ringtail
8 possums we used a purpose built immobilising dart gun or a pole syringe because they do not
usually enter traps (de Tores and Elscott 2010).
Captured animals were placed in cloth bags and transported to the Department of
Environment and Conservation’s Lechanault Field Station where they were anaesthetised
using isoflurane gas anaesthesia. Anaesthesia was first induced with 5% isoflurane and 2
litres of oxygen per minute. When the animals were fully unconscious, the isoflurane was
reduced to 1.5% when anaesthetising brushtail possums, and 2% when anaesthetising western
ringtail possums or brush-tailed phascogales. The oxygen was kept constant at 2 litres of
oxygen per minute. Respiration and heart rate were monitored throughout the anaesthesia.
Figure 1: Aerial photograph of the study site (from Hunter 2012). The blue dots represent the trap sites.
Animals captured on the road alignment, marked in yellow, were relocated to the release site. The
reference site was chosen as it is continuous vegetation that was unaffected by the road construction
activities, while the release site was chosen as it was the nearest continuous vegetation that was as close
as possible to the road alignment where the animals were originally captured.
9 Standard morphometric data including weight, head-body length, pes length, pouch
condition and presence or absence of pouch young for females, and testes width and length
for males were recorded while the animals were sedated. An ear tissue biopsy was also
collected from each animal for genetic analyses. Animals were implanted with microchips or
Passive Integrated Transponders (PITs, Trovan, Central Animal Records, Keysborough,
Victoria).
The two possum species were fitted with movement sensitive mortality collars
(Biotrack Ltd, Dorset, UK; or AVM Instrument Company, Ltd, Colfax, California, USA),
which changed the frequency emitted when the animals had remained still for more than
three to four hours. The brush-tailed phascogales were fitted with Biotrack Ag357 collars
that were too small to include this function. All collars weighed less than 3% of the body
weight of the animals. Animals were released at night at least five hours after recovery from
the anaesthesia. Any non-target species captured were released immediately at the point of
capture except for reptiles found directly on the road alignment, which were relocated to the
reference site.
Clearing for the construction of the road commenced on 19 March 2012 and a fauna
relocator attended with the aim of relocating any animals still left in the vegetation. Any
trees that were within the road alignment were pushed over slowly in the hope that any
animals would be able to escape or to be captured and relocated. Indeed two female western
ringtail possums were found at night on vegetation that had been pushed over during the day.
They were captured, fitted with radio collars and released at the release site. A third western
ringtail possum was spotted by the fauna relocator on the cleared vegetation but it could not
be captured.
Monitoring of animals Radio tracking was conducted using a handheld Sirtrack 3 element Yagi antenna and
battery operated ‘Biotel’ RX3 radio receiver (Bio Telemetry Australia, St Agnes, SA). Both
the day (resting) location and the night location were determined at least once a week for
each animal. Differential GPS locations of the trees on which the animals were found were
recorded using a Thales Mobile Mapper Pro GPS and post processed using the
MobileMapper Office software (Thales Australia, NSW). Each recorded location was also
marked using flagging tape.
Collars of possums that had not moved for several hours transmitted a mortality signal,
and were tracked until the collar was recovered where possible. When a mortality event
occurred, the radio collar and any remains of the animal were collected using sterile gloves.
Radio collars were swabbed for saliva from putative predators and the samples were analysed
at the Helix DNA laboratory (Helix Molecular Solutions Pty Ltd, Leederville WA) to
determine the predator species involved (fox, cat, dog or chuditch) through melt curve
analysis (Berry and Sarre 2007).
Before and during the clearing operations we captured and relocated a total of five
western ringtail possums, three females and two males, which were found directly on the
road alignment. Three male western ringtail possums were captured near the alignment and
released at their point of capture and another six, three males and three females, were
captured at the reference site, one male in March and the other five in July 2012.
Brushtail possums and brush-tailed phascogales were captured at the reference site, but
the only phascogale that was caught near the road alignment managed to remove its radio
10 collar within a day of release and was therefore excluded from the study. Due to this
unbalance in numbers it was possible to an extent to compare the data that were collected at
the reference, treatment and relocation sites for western ringtail possums but not for the
brushtail possums and brush-tailed phascogales.
Statistical analyses Survivorship of the animals at the three different sites was determined using the known
fate model in Program MARK (Cooch & White 2010). The sex of the animal, weight and
head-body length of the animal, average maximum and minimum temperatures between
radio-tracking periods and rainfall were included in the models as additional factors to
determine whether they affected the survival of the animals.
The home ranges of the animals were determined using he 95% kernel contours found
in Ranges 8 (Anatrack Ltd, Dorset, United Kingdom), as this has been determined to be the
most accurate type of home range analysis when appropriate sample sizes and smoothing
parameters are used (Comport et al. 1996). These home ranges of the individuals were then
grouped into their respective species and areas, and an ANOVA was performed to test for
differences in home ranges between species and within species.
Other environmental variables of the area in which the arboreal animals were found in
were also considered, such as the animals’ preferred day/rest location, the species of tree that
the animals were found most often in, how high up the animals were in the tree and general
characteristics of the animals that were radio collared. These variables can help determine
the requirements to maintain an arboreal population in any area and the differences found
between this population of arboreal animals and populations in other locations.
The population size of brushtail possums at the reference site was estimated using a
robust design model in Program Mark. The robust design model used a Huggins closed
capture model and a number of different candidate models for capture probabilities were
compared against each other with the best fitting model was chosen as the one with the
lowest Akaike’s Information Criterion value corrected for small sample sizes (AICc,
Anderson et al. 1994).
Results Three of the five relocated western ringtail possums died during the course of the study,
two due to presumed predation by foxes as shown by the presence of fox DNA on their
collars. The term presumed is used here because the animals could have been scavenged by
foxes after their death. One possum presumably died because its collar became caught on a
branch. However, the carcase could not be retrieved so the cause of death is uncertain (Table
1). Western ringtail possums that were kept on site near the road and those at the reference
site all survived to the end of the study.
Survivorship was markedly different within all models for the relocated western ringtail
possums, with probabilities of surviving the whole of the period on average below 25%
(Table 2). Individual variables, such as the sex, weight and length of the animals had no
impact on the survivorship between these groups.
11 Table 1. Arboreal mammals captured and radio collared at the reference, treatment and release sites within
the study area and their fate by the start of September 2012.
Site Species ID Sex Fate Reference
Reference
Reference
Reference
Brushtail possum
Brushtail possum
Brushtail possum
Brushtail possum
BCF006
BCF012
BCM009
BCM013
Female
Female
Male
Male
Reference
Reference
Reference
Reference
Reference
BCM017
BCM018
BCM019
PCF008
PCF010
Male
Male
Male
Female
Female
Reference
Reference
Reference
Reference
Reference
Reference
Reference
Reference
Reference
Release
Brushtail possum
Brushtail possum
Brushtail possum
Brush-­‐tailed Phascogale
Brush-­‐tailed Phascogale
Brush-­‐tailed Brush-­‐tailed Phascogale
Brush-­‐tailed Phascogale
Phascogale
Ringtail possum
Ringtail possum
Ringtail possum
Ringtail possum
Ringtail possum
Ringtail possum
Ringtail possum
PCF011
PCF015
PCM014
RCF026
RCF027
RCF028
RCM021
RCM029
RCM030
RTF005
Female
Female
Male
Female
Female
Female
Male
Male
Male
Female
Release
Release
Ringtail possum
Ringtail possum
RTF022
RTM001
Female
Male
Release
Release
Treatment
Treatment
Treatment
Treatment
Ringtail possum
Ringtail possum
Phascogale
Ringtail possum
Ringtail possum
Ringtail possum
RTM002
RTF024
PTM003
RTM004
RTM020
RTM025
Male
Female
Male
Male
Male
Male
alive alive alive alive dead(possible fox predation) Alive Alive unknown Alive dead (possible fox predation) Unknown Dead (male d ie-­‐off) Alive Alive Alive Alive Alive Alive Alive Dead (possible fox predation Dead (collar caught in t ree) Dead (possible fox predation) alive unknown alive alive alive Table 2. Survivorship models for western ringtail possums between sites in Bunbury below delta AICc values
of 2.0. Relocated animals had much lower survival rates than the other two groups.
12 Factors included in model AICc ΔAICc Treatment Release Reference Site + Mean min temp + rainfall 35.960 0.00 1.000 0.198 1.000 Site + rainfall 37.337 1.377 1.000 0.208 1.000 Site 37.559 1.599 1.000 0.201 1.000 Site + Mean max t emp + rainfall 37.932 1.972 1.000 0.213 1.000 Only one of the brushtail possums radio tracked at the reference site died during the
study. This was a male and the cause was possibly predation given the nature of the remains
and bite marks found on the collar, but DNA analysis was inconclusive.
Of the five brush-tailed phascogales radio tracked at the reference site, two were
confirmed dead, and another was only ever located on the same tree, both day and night for
four months, suggesting the animal had either been able to remove the collar, or had died in
the tree.
The western ringtail possums radio tracked during the study were found at three distinct
locations corresponding to the treatment, release and reference sites (Figure 2). This shows
that the animals did not move between these sites throughout the study and that relocated
animals moved large distances of up to 1.2km from the original release site.
Figure 2. The locations of individual western ringtail possums radio tracked throughout the study were
clustered in three separate areas corresponding to the treatment (red), release (yellow) and reference
sites (blue). Animals moved up to 1.2km away from the release site while non-relocated animals
remained close to where they were originally found.
The large distances travelled by the relocated western ringtail possums resulted in this
group of animals having the largest home range, of 37.3+29.50ha compared to 8.8±5.40ha at
the treatment site and 2.6±2.00ha at the reference site. However, these differences were not
significant due to the small numbers and large standard errors (p=0.371; Table 3).
13 Table 3. Home range estimates (ha) and standard errors for western ringtail possums radio tracked at the
treatment, release and reference sites. Due to the large standard errors these differences were not
statistically significant.
Site Mean (ha) Standard error Minimum Maximum 8.8 37.3 2.6 5.40 29.50 2.00 0.7 0.8 0.2 19.2 155.0 12.7 Treatment Release Reference Incremental area plots demonstrated that new locations for night tracking were still
frequent by the end of the study, showing that we had not yet reached the extent of their
levels of movement, or the size of their home ranges.
The population of brushtail possums at the reference site was estimated at 21±9.3
individuals. Of the species living at the reference site the brush-tailed phascogales had the
largest home ranges, approximately three times the size of the home ranges of the brushtail
possums and over 15 times the size of the home ranges of western ringtail possums (Table 4).
Table 4. Home ranges estimates (ha) and standard errors of the study species living at the reference site.
Species Western ringtail possum Brushtail possum Brush-­‐tailed phascogale Mean (ha) Standard error Minimum Maximum 2.7 11.2 35.0 2.00 2.60 22.60 0.2 4.1 5.4 12.7 24.3 124.8 Discussion The results of this study indicate that relocating western ringtail possums to an area
unaffected by road development might not be beneficial for this species, especially in the
presence of introduced predators. Two out of five relocated western ringtail possums
succumbed, presumably due to fox predation, soon after they were relocated within the
release site. All of the relocated possums made large movements of up to 1.2km away from
their point of release, possibly in search of optimal habitat or, in the case of males, potentially
searching for females. It is very likely that during these movements the animals had to come
to the ground where they were at much greater risk of predation by foxes.
Foxes were regularly sighted in the area, and half way through the study period a fox
baiting and shooting program was implemented in an attempt to reduce the impact of foxes
on the relocated western ringtail possums. Local farmers also reported that foxes were
prevalent in the area, and implemented their own fox control strategies, but maintained that
the fox problem had not been eliminated, and that foxes were still seen moving through their
lands. After fox control operations started around the road construction site, we did not
observe any more deaths of possums. Foxes have been known to prey on western ringtail
possums despite the specie’s arboreal lifestyle (Jones et al. 1994a, b). Fox predation has
been the cause of many translocation failures in Australia, and it has been suggested that with
effective control of exotic predators many conservation efforts in Australia would be
successful (Cowan 2001; Sheean et al. 2012).
14 The construction of roads can increase the predation risk because predators, in
particular foxes, have been known to utilise clearing tracks and roads to move around (Ramp
et al. 2006; Goosem 2007). The facilitation of foxes into the area may explain the failure to
trap ground-dwelling native animals at the treatment site. Clearing for access ways to the site
had been conducted before trapping started, and might have allowed foxes easy access into
the area. Indeed foxes were observed frequently at night while we were searching for
western ringtail possums in the area to be cleared. The presence of introduced predators at
the treatment site may have also caused brushtail possums that are not known to be trap-shy
to become so. Indeed at least two common brushtail possums were sighted at the treatment
site but all attempts to trap them, including targeted trapping where they had been spotted,
failed. No deaths of radio collared western ringtail possums occurred at either the reference or
the treatment sites, even though the treatment site was directly affected by the road
construction operations. So it appears that the vicinity of heavy machinery, people and noise
during the day when the road construction took place did not affect the short-term survival of
these possums.
Unfortunately there was no replication for this study and sample sizes were extremely
small to draw firm conclusions. The duration of this study was also insufficient to include all
of the seasons, as this study was mostly conducted in winter. For this reason the effects of
seasonal variations in environmental variables such as temperature and humidity on
survivorship could not be properly examined.
A longer study would have been required to improve our estimates for the home ranges
of the study species because incremental area plots showed that asymptotes in the home
ranges had not been reached with the number of locations that we collected. Additionally
because two of the western ringtail possums died within a couple of weeks of being relocated
their home ranges could not be determined.
Many animals have been found to move large distances for some time after they have
been translocated to find an area in which to establish a home range (Cowan 2001; Massei et
al. 2010). In this study the relocated animals moved up to 1.2 km from their point of release
and must have crossed wide stretches of open ground to reach different patches of vegetation,
which would have increased the risk of falling victims to predators.
The home range of an animal should include all the requirements needed by that animal
in its lifetime (Worton 1989). While western ringtail possums are able to make their own
nesting sites in the form of dreys, the western ringtail possums in this study preferred to rest
in tree hollows. The relocated animals in this study might have found it difficult to find
suitable tree hollows and might have therefore wandered further in search of suitable resting
sites (van der Ree et al. 2006). If a shortage of nesting sites was indeed the reason for the
large movements made by the relocated animals, this might be addressed in future relocation
programs by the installation of nest boxes or artificial dreys, which may be used by the
relocated animals (Moore et al. 2010).
There are currently no published reports comparing the survival of relocated animals to
that of animals that were left within at least part of their original home range. Roselan (2009)
reported advantages from the practice of leaving common brushtail possums as close as
possible to their original home range in the only study that attempted to manage this species
on site during the construction of Mandjoogoordap Drive. This was in contrast to Cowan
(2001), who showed that brushtail possums moved extensively, sometimes travelling up to
7km to return to their original home range and Pietsch (1994) and Eymann et al. (2006), who
15 reported that up to 70% of common brushtail possums died within the first week from being
translocated. The above studies, however, were on the common brushtail possum, a species
considered more resilient than the western ringtail possum (Wayne et al. 2005). While the
western ringtail possums in this study did not appear to exhibit homing behaviour, they
moved away from the release site. By contrast, the possums that were retained in their
original home range areas near the road remained in the same area throughout the study.
There have been no other studies of western ringtail possums managed on site during
clearing of their habitat for the construction of a road and further research with a greater
numbers of animals needs to be conducted to determine the best management strategy for this
species.
At the reference site we studied the three species of arboreal marsupials away from the
disturbance of the road construction. Here, the brush-tailed phascogales moved great
distances as shown by their large home ranges. The only male brush-tailed phascogale radio
tracked in this study was also found in one of the treatment traps, over one and a half
kilometres away, during the second round of trapping. Its death in July was an expected
event, as brush-tailed phascogales exhibit the phenomenon of the male die-off, and all males
die after the mating season (Cuttle 1982; Rhind 2002). The female phascogales also travelled
great distances, with one individual even leaving the reference site to move into a small
group of eucalypts 300 metres away.
Compared to the western ringtail possum, brushtail possums are a more mobile species,
and spend time on the ground moving from tree to tree (Wayne et al. 2005). This movement
along the ground may have been the cause of the only brushtail possum’s mortality during the
study. The western ringtail possums in comparison spend very little time on the ground,
which could explain the lack of deaths in the reference site for this species. Unfortunately,
no brushtail possums were caught near the road alignment and the only brush-tailed
phascogale captured near the road lost its collar within a day, so we were unable to study how
the road construction affected these species.
Management Recommendations 1. Wherever possible western ringtail possums should be retained within their original
home range areas and, if possible, should be radio collared and monitored during
the clearing process to ensure that they are not present on trees that are being felled
or on vegetation piles that are being mulched. Alternatively the animals could be
captured and held in captivity during the clearing process to ensure they are not
injured or killed and then returned to their remaining home range area.
2. If relocation of western ringtail possums is required the area that they are released
at should be the subject of feral predator control, particularly for foxes. This
control should start before release and continue for at least several months so that
the animals are less likely to be predated upon while they have to move around to
establish new home ranges.
3. The provision of nest boxes should also be studied for relocated possums to
establish if they are suitable to overcome the potential lack of suitable nesting site
or nesting material. This should, however, include control release sites where nest
boxes are not provided to compare survivorship with and without nest boxes.
16 4. Further research is needed on a larger number of animals to assess the costs and
benefits of relocating western ringtail possums or retaining them in what remains of
their home ranges as management strategies during road construction operations.
5. Research is also required into the behaviour of introduced predators, particularly
foxes, in response to road construction activities, especially clearing. The
experience gained in this study suggests that the activity of foxes increases in the
area around disturbance events such as vegetation clearing for road construction. It
may therefore be beneficial for the conservation of native species in the area around
construction activities to implement fox control before, during and after
construction and/or clearing of vegetation.
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20 Appendix 1 List of animals captured during the project including their location (trap site is applicable or
location where captured), nicknames if collared, sex, microchip or ID and their fate.
Location Species Nickname if collared Sex Microchip/ID Fate/comment 06-­‐Mar-­‐12 06-­‐Mar-­‐12 07-­‐Mar-­‐12 07-­‐Mar-­‐12 T4 T37 T1 T12 Bobtail Rat Bobtail Bobtail 001 002 08-­‐Mar-­‐12 08-­‐Mar-­‐12 08-­‐Mar-­‐12 08-­‐Mar-­‐12 08-­‐Mar-­‐12 09-­‐Mar-­‐12 09-­‐Mar-­‐12 13-­‐Mar-­‐12 13-­‐Mar-­‐12 13-­‐Mar-­‐12 13-­‐Mar-­‐12 13-­‐Mar-­‐12 21-­‐Mar-­‐12 21-­‐Mar-­‐12 21-­‐Mar-­‐12 21-­‐Mar-­‐12 22-­‐Mar-­‐12 23-­‐Mar-­‐12 23-­‐Mar-­‐12 23-­‐Mar-­‐12 27-­‐Mar-­‐12 27-­‐Mar-­‐12 27-­‐Mar-­‐12 27-­‐Mar-­‐12 27-­‐Mar-­‐12 27-­‐Mar-­‐12 27-­‐Mar-­‐12 27-­‐Mar-­‐12 27-­‐Mar-­‐12 27-­‐Mar-­‐12 27-­‐Mar-­‐12 27-­‐Mar-­‐12 28-­‐Mar-­‐12 28-­‐Mar-­‐12 28-­‐Mar-­‐12 T56 T001 T003 T20 T21 T19 T38 T5 T12 T18 T54 T21 T013 T14 C27 C8 C2 C6 C22 C11 C3 C7 C5 C42 ? C41 C18 C32 C21 C17 C8 C33 C26 C21 C42 Phascogale Ringtail Ringtail Bobtail King’s skink Bobtail Rat King Skink Bobtail Magpie Cat King Skink Ringtail Ringtail Brushtail Phascogale Phascogale Brushtail Phascogale Phascogale Brushtail Brushtail Phascogale Phascogale Phascogale Brushtail Brushtail Brushtail Brushtail Phascogale Phascogale Brushtail Brushtail Brushtail Brushtail Conrad Michael Jackson Enrico Romeo Amelia Desiree Minnie Donna Jack Harkness Martha Jones Rose Tyler Anna The Doctor Iantho Sarah-­‐Jane Smith Rory Ricky Micky Jack Harkness Rose Tyler Donna Noble Desiree M M M M F F F F M F F F M M F F M M M M M ? Date Relocated to ref. site Collar found the day 000718AD20 after 000715D1DF Collar stuck in b ranch 00071A0E18 Killed by fox 003 Relocated to ref. site 004 Relocated to ref. site 005 Relocated to ref. site 006 Relocated to ref. site 007 Relocated to ref. site Taken to local vet 008 Relocated to ref. site 000715BC03 Alive 0007158FC2 Alive 000719FE20 Alive 0007158589 Died form h eart condition 00071A1BFA Alive 00071A206F Alive 000719F2BF Alive 000715C167 0006E6BED7 Alive 0007157C52 Alive 00071A2066 000715C488 Alive 000715D725 000715BF7F Killed by fox 000715D776 Alive 00071A2EDB Alive Alive Killed by fox Alive Alive 00071A206F 0007149B13 000715BF7F 21 28-­‐Mar-­‐12 C27 28-­‐Mar-­‐12 C17 28-­‐Mar-­‐12 C43 28-­‐Mar-­‐12 C8 28-­‐Mar-­‐12 C24 28-­‐Mar-­‐12 C5 28-­‐Mar-­‐12 T032 28-­‐Mar-­‐12 T030 28-­‐Mar-­‐12 alignment 28-­‐Mar-­‐12 alignment 28-­‐Mar-­‐12 C3 29-­‐Mar-­‐12 alignment 02-­‐Apr-­‐12 T35 05-­‐Jun-­‐12 T24 05-­‐Jun-­‐12 TP20 06-­‐Jun-­‐12 T19 06-­‐Jun-­‐12 T23 06-­‐Jun-­‐12 T25 06-­‐Jun-­‐12 T18 06-­‐Jun-­‐12 TP20 07-­‐Jun-­‐12 T25 07-­‐Jun-­‐12 T36 07-­‐Jun-­‐12 T17 07-­‐Jun-­‐12 TP7 07-­‐Jun-­‐12 TP20 08-­‐Jun-­‐12 T11 08-­‐Jun-­‐12 T17 08-­‐Jun-­‐12 T18 08-­‐Jun-­‐12 T24 08-­‐Jun-­‐12 TP20 08-­‐Jun-­‐12 TP4 08-­‐Jun-­‐12 TP16 22 Brushtail Phascogale Brushtail Brushtail Brushtail Phascogale Ringtail Ringtail Ringtail Ringtail Brushtail Ringtail Ringtail Magpie Rat Rat Magpie Rat Raven Mouse Magpie Rat Magpie Phascogale Mouse Raven Magpie Magpie Magpie Magpie Phascogale Rat Lucky Othello Felicity Primo Iantho Iantho ? ? M F M F M M F M M F M 00071A2EDB 00071A1BFA 0006C844C2 0006E6BED7 000715D776 0006C870AA 00071A22A4 0006C86924 0007189DD1 00071A22A4 0007190080 000718A4F4 000719F3A1 Killed by fox Alive Alive Alive Died from male d ie-­‐off