Bait-delivered cabergoline for the reproductive control of the red fox (Vulpes vulpes): estimating mammalian non-target risk in south-eastern Australia

Non-Lethal Dose-Response Models Replace Lethal Bioassays for Predicting the Hazard of Para-Aminopropiophenone to Australian Wildlife

Para-aminopropiophenone (PAPP) is a potent methaemoglobin (MetHb) forming agent used for the lethal control of exotic carnivores and mustelids. To assess the sensitivity of Australian wildlife to PAPP we developed an in vivo assay that did not use death as an endpoint. Sub-lethal dose-response data were modelled to predict PAPP doses required to achieve an endpoint set at 80% MetHb (MetHb₈₀). The comparative sensitivity of non-target mammals referenced to this endpoint was found to be highly variable, with southern brown bandicoots (Isoodon obesulus) the most sensitive species (MetHb₈₀ = 6.3 mg kg^-1) and bush rats (Rattus fuscipes) the most tolerant (MetHb₈₀ = 1035 mg kg^-1). Published LD₅₀ estimates were highly correlated with PAPP doses modelled to achieve the MetHb₈₀ endpoint (r² = 0.99, p < 0.001). Most dose-response data for native mammals were collected in the field or in semi-natural enclosures, permitting PAPP and placebo dosed animals to be fitted with tracking transmitters and transponders and released at their point of capture. A protracted morbidity and mortality was observed only in Australian ravens (Corvus coronoides). The combination of sub-lethal dose-response assay and survival data collected in the field provided more relevant information about the actual hazard of pest control agents to non-target wildlife species than laboratory-based lethal-dose bioassays. We discuss the need to replace lethal-dose data with biologically meaningful insights able to define a continuum of toxicological hazards that better serve the needs of conservation and veterinary scientists and wildlife managers.

Toward reliable population density estimates of partially marked populations using spatially explicit mark-resight methods

Camera traps are used increasingly to estimate population density for elusive and difficult to observe species. A standard practice for mammalian surveys is to place cameras on roads, trails, and paths to maximize detections and/or increase efficiency in the field. However, for many species it is unclear whether track-based camera surveys provide reliable estimates of population density.Understanding how the spatial arrangement of camera traps affects population density estimates is of key interest to contemporary conservationists and managers given the rapid increase in camera-based wildlife surveys.We evaluated the effect of camera-trap placement, using several survey designs, on density estimates of a widespread mesopredator, the red fox Vulpes vulpes, over a two-year period in a semi-arid conservation reserve in south-eastern Australia. Further, we used the certainty in the identity and whereabouts of individuals (via GPS collars) to assess how resighting rates of marked foxes affect density estimates using maximum likelihood spatially explicit mark-resight methods.Fox detection rates were much higher at cameras placed on tracks compared with off-track cameras, yet in the majority of sessions, camera placement had relatively little effect on point estimates of density. However, for each survey design, the precision of density estimates varied considerably across sessions, influenced heavily by the absolute number of marked foxes detected, the number of times marked foxes was resighted, and the number of detection events of unmarked foxes.Our research demonstrates that the precision of population density estimates using spatially explicit mark-resight models is sensitive to resighting rates of identifiable individuals. Nonetheless, camera surveys based either on- or off-track can provide reliable estimates of population density using spatially explicit mark-resight models. This underscores the importance of incorporating information on the spatial behavior of the subject species when planning camera-trap surveys.

Trends in anecdotal fox sightings in Tasmania accounted for by psychological factors

There has been little evaluation of anecdotal sightings as a means to confirm new incursions of invasive species. This paper explores the potential for equivocal information communicated by the media to account for patterns of anecdotal reports. In 2001, it was widely reported that red foxes (Vulpes vulpes) had been deliberately released in the island state of Tasmania (Australia), although this claim was later revealed to be baseless. Regardless, by 2013 a total of 3153 anecdotal fox sightings had been reported by members of the public, which implied their distribution was wide. For each month in 2001-2003, we defined a monthly media index (MMI) of fox-related media coverage, an index of their relative seasonal abundance (abundance), and a factor denoting claims of fox evidence (claimed evidence) regardless of its evidentiary quality. We fitted a generalized linear model with Poisson error for monthly totals of anecdotal sightings with factors of year and claimed evidence and covariates of MMI, abundance, and hours of darkness. The collective effect of psychological factors (MMI, claimed evidence, and year) relative to biophysical factors (photoperiod and abundance) was highly significant (χ² = 122.1, df = 6, p < 0.0001), whereas anticipated changes in abundance had no significant influence on reported sightings (p = 0.15). An annual index of fox media from 2001 to 2010 was strongly associated with the yearly tally of anecdotal sightings (p = 0.018). The odds ratio of sightings ranked as reliable by the fox eradication program in any year decreased exponentially at a rate of 0.00643 as the total number of sightings increased (p < 0.0001) and was indicative of an observer-expectancy bias. Our results suggest anecdotal sightings are highly susceptible to cognitive biases and when used to qualify and quantify species presence can contribute to flawed risk assessments.

Fertility control in wildlife: review of current status, including novel and future technologies

Overpopulation of selected groups of animals is widely recognised as an issue that can have adverse effects on several current global problems, such as animal and human health, conservation and environmental changes. This review will, therefore, focus on recent novel contraception together with future technologies that may provide additional contraceptive methods.

Is sodium fluoroacetate (1080) a humane poison?

Sodium fluoroacetate (1080) is widely used for the control of vertebrate pests in Australia. While the ecological impact of 1080 baiting on non-target species has been the subject of ongoing research, the animal welfare implications of this practice have received little attention. Literature relevant to the humaneness of 1080 as a vertebrate pest control agent is reviewed in this paper. Previous authors have largely concentrated on the perception of pain during 1080 toxicosis, giving limited attention to other forms of distress in their assessments. Authors who suggest that 1080 is a humane poison largely base their conclusions on the argument that convulsive seizures seen in the final stages of 1080 toxicosis indicate that affected animals are in an unconscious state and unable to perceive pain. Other authors describe awareness during seizures or periodic lucidity that suggests central nervous system (CNS) disruption cannot be assumed to produce a constant pain-free state. Some literature report that 1080 poisoning in humans is painless and free of distress, but this is contradicted by other clinical studies. Using available data an attempt is made to reassess the humaneness of 1080 using the following criteria: speed and mode of action, appearance and behaviour of affected animals, experiences of human victims, long-term effect on survivors, and welfare risk to non-target animals. It is concluded that sodium fluoroacetate should not be considered a humane poison, and there is an urgent need for research into improving the humaneness of vertebrate control methods in Australia.

Stability of cabergoline in fox baits in laboratory and field conditions

Cabergoline is a potent inhibitor of prolactin release and a potential fertility control agent for foxes. To understand how cabergoline could behave in baits deployed for fox control, we conducted laboratory and field trials to investigate the stability of cabergoline when (1) in solution, (2) injected into a bait (deep-fried liver and Foxoff®) and (3) exposed to a range of environmental conditions, including burial. Cabergoline, dissolved in a 1% acetic acid solution, and its carboxylic acid hydrolysis product can be assayed using high-performance liquid chromatography. When stored at 4°C and at room temperature, cabergoline in solution was stable for up to 36 days. When stored under cool (≤15°C), dry conditions, cabergoline (800 µg) in commercial Foxoff® and deep-fried ox-liver baits was stable for 28 and 7 days, respectively; stability was reduced by increases in temperature (tested up to 40°C) and humidity. Recovery of cabergoline from buried baits exposed to a range of field conditions decreased rapidly in the first week, but after 56 days remained detectable at levels of 6–22% of the injected amounts. This study has important implications for baiting campaigns that use cabergoline for fox control.

Home range, habitat selection and diet of foxes (Vulpes vulpes) in a semi-urban riparian environment

Between 2000 and 2002 the home range, habitat selection and diet of foxes were examined in the Dandenong Creek Valley, Melbourne, Australia. The mean home range was 44.6 ha (range 19.2–152.6 ha). A significant selection towards blackberry and gorse used as diurnal shelter was found during the day with an active avoidance of less structurally complex vegetation types. Although there was obvious selection of certain habitats, the diet of the foxes was highly general and opportunistic and thus offers little potential as a factor to manipulate in order to reduce fox abundance. Given the strong preference for blackberry and gorse as a shelter resource, a habitat-manipulation strategy is suggested whereby patches of blackberry and gorse are removed and replaced with less structurally complex vegetation. Such a strategy has the potential to influence the density of foxes in semi-urban riparian environments such as those discussed in this study.

Prolactin in the brushtail possum (Trichosurus vulpecula): development of homologous radioimmunoassay using recombinant possum prolactin

We report the production of recombinant possum prolactin (posPrl), and its use in the development and validation of a highly specific homologous radioimmunoassay for the measurement of prolactin (Prl) in brushtail possums. This enabled the subsequent investigation of some basic mechanisms involved in the regulation of Prl secretion in this species. Recombinant posPrl spanning the entire coding region was expressed in Escherichia coli, resulting in a 199 amino acid protein with a molecular weight approximately 23 kDa. The potency of posPrl was 45.3 +/- 4.8% that of ovine Prl in a radioreceptor assay using possum mammary gland receptors and induced a 3.4 +/- 0.8-fold increase in progesterone secretion in primary possum granulosa cells. Antiserum (G27) was raised against recombinant posPrl and was highly specific for possum Prl (approximately 30% binding at 1:60,000 final dilution), and exhibited negligible cross-reactivity (<0.0001%) with possum growth hormone. Serial dilutions of pituitary gland extracts, and plasma samples from male and female possums gave parallel inhibition curves to recombinant posPrl standards in the assay. Biological validation of the RIA included treating possums with drugs known to alter Prl secretion in other mammals. In seasonally anoestrous female possums, administration of 20 microg thyrotropin-releasing hormone (TRH) resulted in a 15-fold increase (P < 0.01) in plasma Prl concentrations. In mid-late lactating female possums, a bolus of cabergoline (dopamine agonist; 75 microg) reduced (P < 0.05) plasma Prl levels to baseline for 24 h, while repeated administration (6 x 75 microg at 12 h intervals) suppressed (P < 0.01) plasma Prl concentrations until 24h after the last injection. Prolonged inhibition of Prl levels subsequently caused marked (P < 0.01) attenuation in rate of bodyweight increase of pouch young. The amplitude of the Prl surge in response to a bolus of TRH (15 microg) was 5-fold lower in cabergoline-treated, compared to control mid-late lactating possums. In conclusion, we report the development and validation of a robust and sensitive RIA for measuring Prl concentrations in the plasma of brushtail possums.

Increasing the target-specificity of the M-44 ejector by exploiting differences in head morphology between foxes and large dasyurids

The M-44 ejector (ejector) is a more target-specific means of lethal control of red foxes (Vulpes vulpes) than conventional meat baits, which may expose a wide range of non-target species to the bait toxicant. Owing to the threshold pulling force required to activate the ejector, undesired exposure is eliminated in many smaller animals that cannot generate this force. However, the spotted-tailed quoll (Dasyurus maculatus) and the Tasmanian devil (Sarcophilus harrisii) remain potential non-target species because of their larger size. In this study, we report on the development of a collar that excludes devils and quolls by exploiting differences in their head morphology relative to that of red foxes. The collar potentially prevents bait removal by larger non-target species, while still allowing all adult foxes access to the bait to trigger the ejector mechanism. Spotted-tailed quolls small enough to access the bait are theoretically too small to trigger the ejector mechanism set at a threshold pulling force of 2.7 kg.

Predicting mammalian target-specificity of the M-44 ejector in south-eastern Australia

Meat-based baits are currently used for the control of the exotic red fox (Vulpes vulpes) in south-eastern Australia. Thirty-one quadrupedal endemic mammals are considered to be potentially bait consuming (PBC) and may be exposed to bait toxicants. Mechanical toxicant ejectors may be more selective if some PBC species cannot apply enough upward force to trigger them. A simple relationship between body mass and pulling force was sought to enable estimates of ejector specificity to be made. The pulling force applied to ejector baits was measured for the red fox and six endemic mammals. The relationship between body mass and pulling force was highly significant (P < 0.001) and the resulting regression equation was used to estimate the highest pulling forces for 31 quadrupedal mammals based upon the largest body mass recorded for each species. In a sample of 640 foxes, taken by a range of methods in south-eastern Australia, the lowest adult body mass detected from January to September was 3 kg and declined only when cubs were present in the population from October to December. An ejector trigger force of 26.46 N was estimated to allow foxes weighing >3 kg to trigger the device, while eliminating exposure of 26 of the 31 PBC mammals. Appropriate toxicant selection and dose rates may ensure that four out of five susceptible mammals are less likely to be affected by unwanted exposure.

Fox control using a para-aminopropiophenone formulation with the M-44 ejector

The M-44 ejector (‘ejector‘) has proven to be a highly target-specific means of delivering toxicants to the exotic European red fox (Vulpes vulpes) in south-eastern Australia. Para-aminopropiophenone (PAPP) is a potent methaemoglobin (MetHb) forming compound in canids. A formulation of PAPP, dimethylsulphoxide (DMS0) and condensed milk was investigated as a new toxicant formulation for delivery by the ejector. Dosage of eight foxes in the laboratory with a sequential dose demonstrated that the formulation caused a dose-dependent and rapid elevation of MetHb. A strong inverse correlation between MetHb and oxyhaemoglobin concentrations was detected in each case. The symptoms of the toxicosis in the laboratory included progressive cyanosis, lethargy and then collapse when MetHb levels reached 56-76%. A polynomial model was a good fit for describing the relationship between sub-lethal doses of PAPP and the resulting peak MetHb levels. In a pen trial, an ejector was fitted with a bait and loaded with a standard dose of 226 mg PAPP in the same formulation and set at one end of a pen. After voluntarily triggering the ejector, all five foxes in this trial became progressively more lethargic and either lay prostrate or collapsed after 14-25 min, and death was confirmed after a mean of 43 min. We compared some clinical features of PAPP toxicosis with 15 cases of lethal sodium fluoroacetate (1080) poisoning using 0.5 mg kg-1 1080. PAPP produced a mean time to death that was 7.7 times faster than 1080, with the onset of first symptoms being 15 times faster. It was associated with much less activity prior to death and convulsions, spasms and paddling commonly associated with 1080 poisoning after collapse were not detected during PAPP toxicosis. We conclude that the PAPP formulation appears to be a rapidly acting and apparently humane lethal agent for fox control when used in conjunction with the ejector.