1
Assumptions in relation to Foxes in Tasmania
Prepared by: David Obendorf, March 2009
Decisions on fox control in Tasmania have often needed to be made in the face of
inadequate or imperfect knowledge. To assist this decision-making process, a range of
assumptions have been made.
In addition assumptions made in the past need to be continually reviewed to see if they
are still valid.
The purpose of this paper is to outline the assumptions made on the presence of foxes and
their ecology and provide a starting point to review these assumptions.
This paper has been developed through retrospective research of the documented
incidents, the timelines and through a consultative process to ensure the assumptions are
as robust as possible.
To assist review, assumptions made in 2002 are listed below in Table 1.
Any problematic or unresolved issues in these assumptions are taken up in the assumptions
listed in Appendix 1 to this paper.
There are a number of current questions relating to fox entry, establishment and spread
that require greater clarity. In most cases there is still no conclusive evidence available
to answer these. This means that to develop management requirements some
assumptions must be made. Where an assumption can not confidently be made, a
precautionary approach needs to be taken.
Questions that require answers:
 Are there free-ranging foxes currently in Tasmania? Yes/No Reliability rating
 How long have foxes been living in Tasmania? Before 1970, since at least 1970’s, only
after 2000/2001
 What are the likely routes of entry of live foxes into Tasmania?
 What are the basic requirements for foxes to successfully establish in Tasmania?
 What environmental factors would foxes living in Tasmania - prior to ~19981 - have
been exposed to?
 Currently, what is the relative risk of different routes for the entry of foxes into
Tasmania (i.e. a risk categorisation)?
 If foxes are present and widely distributed in Tasmania, can the use of 1080-meat baits
eradicate foxes?
1
In May 1998 a live fox disembarked from a Brambles freight ferry at the port of Burnie, NW Tasmania
Prepared by: Dr David Obendorf, Wildlife Veterinarian BVSc(Hons), B(A)Sc, PhD
Address: 7 Bonnington Road, West Hobart, TAS, 7000; email: davidobendorf@tassie.net.au Phone: 03 6234 5561
2
Appendix 1 (pages 4-9) looks at the validity of a range of assumptions that have been or
could be made.
The paper explores the assumptions supporting a fox control program that has now run for
over 7 years. It categorises each assumption as (1) an invalid assumption based on current
knowledge, (2) a valid assumption based on current knowledge or (3) a known fact. This
mechanism provides an objective basis to examine what support exits for an assumption,
and logically progresses an assumption to a fact, or discounts them.
Also attached to the paper are tabulated fox incidents:
Attachment 1 - Fox incidents involving the collection of forensic material with follow-up
investigation. [TASMANIAN FOX TIMELINE & INCIDENTS 2001-2009.doc]
This was an earlier attempt to look at known facts and assumptions in relation to assessing
the fox risk for Tasmania.
Attachment 2 - Investigations of specific incidents involving the recovery of biological
material derived from or identified as ‘fox’ in Tasmania. [Fox incidents involving the
collection of forensic material with follow-up investigation.doc]
The Conclusion (pages 10-13) uses an accepted risk assessment matrix for defining the
likelihood of an unwanted incursion as well as qualifying the consequences of foxes for
Tasmania
Prepared by: Dr David Obendorf, Wildlife Veterinarian BVSc(Hons), B(A)Sc, PhD
Address: 7 Bonnington Road, West Hobart, TAS, 7000; email: davidobendorf@tassie.net.au Phone: 03 6234 5561
3
Table 1 - Assumptions made in 2002
Assumption
1. Live foxes are capable of entering
Tasmania
2. Live foxes have been seen freeranging in Tasmania.
3. Forensic evidence has linked the
presence of foxes in Tasmania to
specific locations in Tasmania.
4. Foxes have established and are
breeding in Tasmania.
5. The use of buried 1080-dried meat
baits is an effective tool for the
eradication of foxes in Tasmania.
6. Foxes exist at various locations
across Tasmania at very low
densities.
Justification
This is supported by the 31 May 1998
incident when a fox from Melbourne
travelled to Tasmania on a freight
vessel; the fox disembarked at the
Port of Burnie and was free-ranging
in the city and inner suburbs.
This is supported by the index
incident
reported
by
wildlife
biologist, Chris Spencer in May 2001
when he sighted a fox on Illawarra
Road in the Longford/Hadspen area.
Subsequently, a wildlife consultant,
Steve Cronin reported sighting a fox
at the rural property ‘Brambletye’
[near Conara] in September 2002.
This is supported by a number of
reported incidents involving the
recovery of a decomposed fox
carcass presumably shot on site in
September 2001. [see Attachment
1.]
Not supported by evidence in 2002.
No physical evidence that any baiting
at these sites has killed foxes.
Focus of alleged sightings in the
Northern Midlands. Not supported by
physical evidence in 2002. [Beginning
in 2005 and increasing to 2008, the
Fox
Eradication
Program
has
reported the recovery of scats
confirmed by DNA analysis to be fox
from Seymour & Gladstone in NE
Tasmania; near Oatlands, Conara,
Campbelltown in the Midlands;
Spreyton, Burnie and Barrington in
NW Tasmania].
Prepared by: Dr David Obendorf, Wildlife Veterinarian BVSc(Hons), B(A)Sc, PhD
Address: 7 Bonnington Road, West Hobart, TAS, 7000; email: davidobendorf@tassie.net.au Phone: 03 6234 5561
4
Appendix 1 - Assumptions on Foxes
1) Foxes have entered Tasmania
Known fact /valid assumption on current knowledge/invalid assumption
Dependant on the following other assumptions

Impact of assumption on management
 A significant unwanted vertebrate warranting eradication [the basis of Action
Plan to prevent European red fox into Tasmania 2001-2003 - DPIW July
2001; author: Sally Bryant]
Information to support
 Historically there are a number of documented and corroborated instances
where foxes were released at specific Tasmanian sites during the 19 th century
[see Action Plan (p5) - 19th & 20th century fox releases in agricultural districts
for sport.]
 Most recently this is supported by the July 1998 incident when a fox from
Melbourne travelled to Tasmania on a freight vessel; the fox then disembarked
at the Port of Burnie.
Conflicting information
 None
Information to further validate assumption
 Not required
2) Live mixed-sex foxes were intentionally and covertly introduced &
released into Tasmania within the last decade
Known fact/valid assumption on current knowledge/invalid assumption based on current
knowledge
Dependant on the following other assumptions
 Tasmania is an island and foxes require the agency of humans to enter
Tasmania.
 The agencies of entry include overt and intentional; covert and intentional; or
unintentional/accidental.
Prepared by: Dr David Obendorf, Wildlife Veterinarian BVSc(Hons), B(A)Sc, PhD
Address: 7 Bonnington Road, West Hobart, TAS, 7000; email: davidobendorf@tassie.net.au Phone: 03 6234 5561
5

Target areas of interest include ingress ports for containerised freight, vehicles
and travelling public.
Impact of assumption on management
 Given that the Tasmanian environment provides ample food & survival resources
of day-to-day existence and given their short life span, their continued intergenerational presence in Tasmania would require successful breeding.
 If proven, the intentional release of mixed sex foxes at several sites in the early
years of 21st century [2000 & 2001] would be the most significant basis for a
publicly-funded eradication program.
Information to support
 DPIW official prepared a dossier of information [Confidential Ministerial
Briefing Note - June 2001] based on a reported conversation with the principle
informant who named three suspects as being involved in this covert smuggling,
rearing and release activity.
Conflicting information
 Mid-year 2001 a Police Taskforce used the information provided by DPIW officials
to commence an investigation. The Taskforce was unable to find any
corroborative evidence to substantiate the allegation of malicious intentional
introduction of fox cubs and the release of foxes within Tasmania.
Information to further validate assumption
 Several individuals with family or community connections to rural properties
and/or horse & hound hunt clubs have alleged that live foxes were smuggled
into Tasmania for fox-hunting. These reports go back as far as the 1940’s.
 At least one individual [Don Davey of Launceston] has confidently recalled
seeing, on one occasion, three fox carcasses on the back of Land Rover utility in
the early 1970’s. [The Midlands property and the exact origin of these foxes
were not divulged.]
3) Foxes have existed, in recent times, in Tasmania
Known fact /valid assumption on current knowledge/invalid assumption
Dependant on the following other assumptions
 Tasmania is an island and foxes require the agency of humans to enter Tasmania
(by overt, covert or inadvertent means)
Prepared by: Dr David Obendorf, Wildlife Veterinarian BVSc(Hons), B(A)Sc, PhD
Address: 7 Bonnington Road, West Hobart, TAS, 7000; email: davidobendorf@tassie.net.au Phone: 03 6234 5561
6
Impact of assumption on management
 Given that the Tasmanian ecology provides ample natural foods & habitats of
day-to-day existence, their continued inter-generational persistence requires
successful breeding and survival under existing Tasmanian conditions.
 Re-introductions of foxes by various routes of entry would require ongoing
surveillance and management.
Information to support
 This is supported by the index incident reported by wildlife biologist, Chris
Spencer in May 2001 when he sighted a fox on Illawarra Road in the
Longford/Hadspen area. Subsequently, wildlife consultant, Steve Cronin
reported sighting a fox at the rural property ‘Brambletye’ [near Conara] in
September 2002.
 The Fox-free Taskforce has complied listings of witnesses who have reported
alleged sightings of foxes; some of these sights have been rated as ‘excellent’.
The Taskforce has recorded more than 1500 fox sightings.
 There are reports from the general public who allege sighting single foxes in
earlier decades (as far back as 1970s).
Conflicting information
 None
Information to further validate assumption
 Collate and review existing data and assess reliability and focussing field efforts
in validation.
4) Forensic evidence links the presence of foxes to specific locations in
Tasmania
Known fact/valid assumption on current knowledge/invalid assumption
Dependant on the following other assumptions
 Assumes that the fox evidence is derived from local Tasmanian sites.
 Assumes the testimonies of the initial reporters are logically & scientifically
consistent with the time-space continuum of the forensic material collected
from the site.
 Assumes the physical evidence has not been falsified, fabricated and planted.
Impact of assumption on management
 Assumes that foxes occur (or occurred) at the site of recovery of confirmed
forensic evidence. [For example: DNA-positive fox scat is directly correlated to
the occupancy of foxes at that site; DNA-positive fox material (blood) is directly
correlated to its deposition by a fox at the site of recovery.]
Prepared by: Dr David Obendorf, Wildlife Veterinarian BVSc(Hons), B(A)Sc, PhD
Address: 7 Bonnington Road, West Hobart, TAS, 7000; email: davidobendorf@tassie.net.au Phone: 03 6234 5561
7
Information to support
 The Fox-free Taskforce has investigated several incidents involving the recovery
of fox remains [see Appendix 2].
 The Fox Eradication Program has collected carnivore scat from various parts of
Tasmania since 2005. To date upwards of 27 DNA-positive fox scats have been
identified.
 In March 2009 Fox Eradication Program reported that 5 of 25 Tasmanianrecovered DNA-positive fox scats had been genotyped and gender identified.
Conflicting information
 Independent forensic reviews of these incidents, including access to the
documentary evidence used by the FFTF, has questioned the authenticity of
original accounts of events; the chain of custody of evidence; the failure to keep
vital evidences for review; the forensic conclusions drawn about the time, cause
and place of presumed death of these foxes.
 In the case of the DNA-positive fox scats, no contemporaneous additional (and
distinctly site-specific) evidence of fox presence at these sites is available (e.g.
foot prints at sand traps, remote-sensor camera images, actual foxes, denning
locations etc).
Information to further validate assumption
 Review & independently assess important evidences and supporting
documentation
5) Foxes are breeding in Tasmania
Known fact/valid assumption on current knowledge/invalid assumption
Dependant on the following other assumptions
 Assumes the presence of both male and female foxes
 Assumes foxes can survive and reproduce successfully in Tasmania under
prevailing environmental conditions [including in the presence of Tasmanian
devils and the use of vertebrate poisons such as Compound 1080].
Impact of assumption on management
 Irrespective of any further introductions of foxes into Tasmania, any existing
foxes (of both genders) are capable of reproducing in the wild.
Information to support
 The recovery of dried remains of a juvenile fox recovered from the Bass Highway
at Lillico in February 2006.
Prepared by: Dr David Obendorf, Wildlife Veterinarian BVSc(Hons), B(A)Sc, PhD
Address: 7 Bonnington Road, West Hobart, TAS, 7000; email: davidobendorf@tassie.net.au Phone: 03 6234 5561
8

In March 2009 Fox Eradication Program reported that 5 of 25 Tasmanianrecovered DNA-positive fox scats were all derived from a different fox and that
three scats came from male foxes and one from a female fox with another
indeterminate.
Conflicting information
 Follow-up field searches in the vicinity of the Lillico fox (for the breeding den,
other siblings, predator kills etc) or forensic material collected (scats, hair and
footprints) did not confirm the existence of foxes in the vicinity.
 Government FEP website later suggested that the juvenile fox had been shot by
an anonymous rabbit shooter and transplanted to the road side in order to be
found.
 So far male and female fox scats have not been recovered in the same locality,
although the distance between these gender-identified fox scats is <50km.
 In the case of the 5 gender-identified fox scats, no contemporaneous additional
(and distinctly site-specific) evidence of fox presence at these sites is available
(e.g. foot prints at sand traps, remote-sensor camera images, actual foxes,
denning locations etc).
Information to further validate assumption
 Community intelligence of fox breeding activity - sightings, fox calls (in mating
season), targeted use of fox-scent detector dogs, sand traps, remote sensor
cameras, etc
6) Tasmanian foxes have been ‘controlled’ to very low numbers by
Compound 1080 poison
Known fact/valid assumption on current knowledge/invalid assumption
Dependant on the following other assumptions
 Foxes are highly sensitive to sodium monofluoroacetate [Compound 1080] both
through access to 1080-poisoned carrion and direct targeting through 1080-meat
baits.
 If foxes were present in Tasmania in the period when Compound 1080 was
widely used in rural and forestry areas of browsing animal control (1953-2002),
then their numbers would be reduced through access to 1080 poisoned
carcasses.
Impact of assumption on management
 Foxes scavenging on wildlife carcasses killed by Compound 1080 poison are
invariably killed.
 This assumption would in part explain the assumed low density of foxes in
Tasmania.
Prepared by: Dr David Obendorf, Wildlife Veterinarian BVSc(Hons), B(A)Sc, PhD
Address: 7 Bonnington Road, West Hobart, TAS, 7000; email: davidobendorf@tassie.net.au Phone: 03 6234 5561
9
Information to support
 Scientific evidence confirm the high sensitivity of foxes for 1080 LD50 ~ 0.09
mg/kgm body weight.
 Domestic dogs, another canid, have been regularly killed through ingestion of
1080-poisoned wildlife carcasses in Tasmania.
Conflicting information
 No fox carcasses have been recovered in the areas intensively 1080-baited to kill
foxes (see Map).
Information to further validate assumption
 If required, collaboration with Invasive Animal CRC & Vertebrate Pest Unit,
Victorian DPI at Frankston to conduct feeding trials with captive foxes.
7) Foxes in Tasmania can be eradicated by the use of buried 1080-meat
baits
Known fact/valid assumption on current knowledge/invalid assumption
Dependant on the following other assumptions
 Foxes are present in Tasmania (in low numbers)
 Foxes in Tasmania are the result of local breeding
Impact of assumption on management
 Are foxes present in Tasmania - at low densities with ample food resources likely to detect and eat buried 1080-meat baits?
 Would any foxes present in Tasmania be more likely to be killed by ingesting
1080 meat baits than through access to 1080-poisoned wildlife carcasses [i.e.
secondary poisoning via carrion feeding]?
Information to support
 Scientific evidence confirm the high sensitivity of foxes for 1080 LD50 ~ 0.09
mg/kgm body weight. This meat-bait delivery system is likely to be more
successful where fox numbers are high and natural food resources scarce.
Conflicting information
 There is no evidence to confirm that foxes can be eradicated by the use of 1080meat baits over a land mass the size of Tasmania.
 There is no instance where foxes were eradicated even with intensive bait
programs using very frequent delivery of unburied baits over large areas
occupied by foxes.
Prepared by: Dr David Obendorf, Wildlife Veterinarian BVSc(Hons), B(A)Sc, PhD
Address: 7 Bonnington Road, West Hobart, TAS, 7000; email: davidobendorf@tassie.net.au Phone: 03 6234 5561
10
Information to further validate assumption
 Initially the FFTF used a commerically prepared dried kangaroo meat bait 2 as
the substrate for the 1080-fox baits used in Tasmania. In more recent years the
FEP has commenced using the commercial Foxoff™ baits. Research suggests that
the palatability of the Foxoff™ baits for foxes is vastly inferior to the dried meat
baits with field trials demonstrating that foxes are more likely to bury these
Foxoff™ baits rather than eating them3.
8) Foxes exist in various parts of Tasmania at very low densities
Known fact /valid assumption on current knowledge/invalid assumption
Dependant on the following other assumptions
 Foxes have entered Tasmania and been reliably seen at various locations [i.e.
high credibility witnesses with very good fox recognition skills - Chris Spencer,
Steve Cronin].
 That foxes have dispersed from another established site and/or have reproduced
locally.
Impact of assumption on management
 If this assumption is correct then it questions the effectiveness of current
control strategies using 1080 buried-meat baits.
 If this assumption is correct, then there are valid grounds for enacting
legislation specifically related to the control/eradication of foxes on all
Tasmanian land tenures.
Information to support
 As of March 2009 the Tasmanian Fox Eradication Program has reported the
recovery of 27 scats confirmed by DNA analysis to be fox [Seymour & Gladstone
in NE Tasmania; near Oatlands, Conara, Campbelltown in the Midlands;
Spreyton, Burnie and Barrington in NW Tasmania].
Conflicting information
 No supporting photographic evidence of live foxes in Tasmania.
 No foxes shot by recreational hunters after 2001.
 Three separate $1000 fox rewards remain unclaimed since they were
implemented in September 2006.
Information to further validate assumption
 Deployment of infra-red sensor and camera units at scat location sites.
 Follow up use of fox-sniffer detector dogs at scat location sites.
2
Manufactured in Western Australia
von Polanen Petel et al (2001) Bait palatability influences the caching behaviour of the red fox (Vulpes vulpes).
Wildlife Research 28: 395-401.
3
Prepared by: Dr David Obendorf, Wildlife Veterinarian BVSc(Hons), B(A)Sc, PhD
Address: 7 Bonnington Road, West Hobart, TAS, 7000; email: davidobendorf@tassie.net.au Phone: 03 6234 5561
11
Conclusion
From the perspective of assessing the risk of foxes in Tasmania this review uses an
accepted risk assessment matrix for defining the likelihood of an unwanted incursion as
well as qualifying the consequences of foxes for Tasmania4.
Likelihood
It is factually proven that the likelihood that single foxes, from time to time, have gained
access to Tasmania by unintentional means - namely via bulk rural commodity shipments
and containerised freight from a fox-infested hub in the port of Melbourne. The likelihood
of entry risk is considered moderate to high.
Inadequate biosecurity and quarantine measures as the explanation for the sighting of live
foxes in Tasmania contrasts with the official explanation offered by the State
Government; namely a conspiracy to covertly smuggle fox cubs into Tasmania, rear them
in secret and then release them into the environment.
A third likelihood scenario relates to the possibility that single-gender foxes have been
deliberately introduced into Tasmania in the past.
Consequence
The consequences of fox establishment in Tasmania is universally agreed to be
potentially serious to biodiversity; establishment means successful breeding.
On this basis the risk assessment matrix would determine that there is high to very high
justification for preventing the entry, establishment and spread of foxes in Tasmania.
That said the assessment takes into consideration efforts to prevent the entry threat
through biosecurity measures in the form of port quarantine measures, inspections of
transport, freight and passenger vehicles arriving from fox endemic locations (i.e. from
Victoria) and through public awareness activities.
As this assumption review highlights, the eradication of the foxes that are believed to
exist in Tasmania relies on (1) accurate and verifiable bio-intelligence confirming the
presence of fox at a given site and (2) the use of effective tools for their detection and
elimination.
4
Binder, M (2002) The Role of Risk and Cost-Benefit Analysis in Determining Quarantine Measures. Productivity
Commission 2002; AFFA (Department of Agriculture, Fisheries and Forestry - Australia) 2000 Draft Import Risk on
the Importation of Apples from New Zealand, Biosecurity Australia [October 2000]
Prepared by: Dr David Obendorf, Wildlife Veterinarian BVSc(Hons), B(A)Sc, PhD
Address: 7 Bonnington Road, West Hobart, TAS, 7000; email: davidobendorf@tassie.net.au Phone: 03 6234 5561
12
The State Government fox eradication program has consistently referred to the ‘presence’
of foxes and not the ‘establishment’ of foxes.
The implicit in the Government’s policy is the assumption that if foxes have been
continuously present in various locations across Tasmania for at least the last 7 years,
then they must have reproduced, established themselves within the landscape and spread
to other regions.
As discussed in this paper the occurrence of single foxes does not constitute a breeding
population of foxes and greater emphasis has to be directed into firstly confirming that
foxes are breeding in Tasmania and secondly, if they are reproducing in Tasmania, what
has kept that population at such cryptic levels for so long?
If foxes have not reproduced in Tasmania then the only alternative explanation for their
continued presence (and the ongoing sightings) would be the continual introduction of
additional foxes. That would suggest that the State biosecurity measures for foxes are still
insufficient to prevent new incursions of foxes.
And the only explanation for the continued presence of foxes that are not reproducing
would be that the foxes have remained isolated as single animals, or are sterile, or are all
of one gender.
The recent information suggesting that fox scats of both sexes have been recovered from
sites in Tasmania would suggest that breeding potential exists. After 7 years of the
Government’s program the presence of their excreta and the lack of factual foxes is,
however, hard to comprehend.
Currently the State Government has identified several ‘hotspot’ locations where, based on
recurrence of suspicious incidents with evidence of fox presence, it is assumed that more
than one fox may be present.
Currently the program has also not been able to prove that foxes have reproduced at any
hotspot site, although it is assumed.
Currently the State Government’s only fox eradication tool is the deployment of buried
1080-meat baits. The use of this tool assumes that the foxes present in a given hotspot
will discover one of these baits, eat it and die.
There is no recorded evidence that the use of 1080-meat bait has eradicated foxes once
they have established breeding populations in new territories with ample food resources.
The difficulties the current program faces are manifold.
Prepared by: Dr David Obendorf, Wildlife Veterinarian BVSc(Hons), B(A)Sc, PhD
Address: 7 Bonnington Road, West Hobart, TAS, 7000; email: davidobendorf@tassie.net.au Phone: 03 6234 5561
13
Firstly, knowing as fact that foxes have successfully entered Tasmania - and perhaps have
done so on numerous occasions for many decades - yet having no clear evidence of the
establishment of local reproducing fox populations. Why?
Secondly, the assumption that there are several foxes present in several hotspot sites
[based on incidents and evidence] and applying a control tool on an ad hoc & arbitrary
basis - a tool for which there is no evidence can successfully eradicate the targeted
species.
Recommended priorities for useful action are:




Developing a suite of diagnostic and forensic methods to confirm the presence of foxes
at identified ‘hot-spot’ sites.
Collection of bio-intelligence on the establishment of mixed-gender foxes at identified
‘hot-spot’ sites.
The effectiveness of current control/eradication strategies employed in Tasmania.
Enacting special legislation to support the eradication of foxes across all Tasmanian
land tenures.
Prepared by: Dr David Obendorf, Wildlife Veterinarian BVSc(Hons), B(A)Sc, PhD
Address: 7 Bonnington Road, West Hobart, TAS, 7000; email: davidobendorf@tassie.net.au Phone: 03 6234 5561