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

Abstract

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.

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

“…Theoretical analysis suggests that the proposed collar in combination with a suggested ejector activation force of 2.7 kg (Marks and Wilson 2005) can exclude all Tasmanian devils and spotted-tailed quolls from exposure to ejector toxicants. All devils in our sample were 'excluded' by the collar, but as only a single devil cub was available this result should be treated with caution until a larger sample of juvenile animals is available.…”

“…Further investigations are also required to determine the exposure risk of domestic animals using the 'collared' ejector. The present study uses the pull force equation generated by Marks and Wilson (2005). Marks and Wilson (2005) related body weight to the potential pull force of individual animals; however, variation in pull force between individuals of one species was not investigated.…”

“…This distance was used to determine the length of the collar that allowed access to a bait by foxes but ensured exclusion of devils and quolls. Previous research (Marks and Wilson 2005) showed that pulling force is allometrically related to body mass, as described by a general regression equation for quadrupedal species. The weight of any animal not excluded by the final collar design was used to predict the pulling force of which they were capable and their consequent ability to trigger an ejector set at the pull force threshold of 2.7 kg.…”

“…When an animal taking the bait exerts a pulling force that exceeds a certain force threshold, the ejector mechanism is triggered and a toxicant is propelled into the animal's mouth. The ejector mechanism is activated at a force between 1.6 and 2.7 kg (Connolly and Simmons 1984) and this excludes most native carnivores and omnivores such as Antechinus sp., bandicoots (Peramelidae) and eastern quolls (Dasyurus viverrinus) from being exposed to the bait toxicant (Marks and Wilson 2005). Although these animals can still access and consume the unpoisoned bait on the ejector, no exposure to the toxicant will occur because they are unable to trigger the mechanism.…”

Reintroduction of Tasmanian devils to mainland Australia can restore top-down control in ecosystems where dingoes have been extirpated

“…Nominal dose for dingoes is 6 mg of pure 1080 per bait (Fleming and Parker, 1991). Intensive fox control is achieved with 1080 meat baiting, nominal dose 3 mg of 1080 per bait (Claridge et al, 2010;Marks and Wilson, 2005). In the model we simulate this scenario by holding dingo and fox abundance at 0.…”