Responses of dingo (Canis familiaris) populations to landscape-scale baiting

Activity May Not Reflect the Numbers: An Assessment of Capture Rate and Population Density of Dingoes (Canis familiaris) Within Landscape-Scale Cell-Fencing

Most human-carnivore conflicts arise from the impact of predation on livestock. In Australian rangelands, considerable resources are allocated to constructing exclusion fences and implementing control measures to manage dingo populations for sustainable livestock enterprise. Assessing the effectiveness of these measures is crucial for justifying the investment. We used a replicated experimental design to examine the effect of landscape-scale dingo-proof exclusion fences ('cell-fencing') on activity and population density of dingoes in the Southern Rangelands of Western Australia. We monitored dingo populations for 22-24 months across six study sites nested within a landscape of about 75,000 km2 and defined 'fence level' as the number of dingo-proof fences enclosing each study site. We used camera trap capture rate (number of independent capture events per 100 trap nights) as a metric for dingo activity (including the availability of resources as other potential covariates), estimated dingo density using spatially explicit mark-resight models, and tested the relationship between capture rate and estimated density of dingoes for each study site. Significant variation in both metrics was observed between sites and across time. Fence level and prey occurrence significantly influenced dingo activity. The annual mean dingo density estimate across study sites was below two dingoes per 100 km2 (i.e., 0.02 dingoes per km2; the maximum value believed to be compatible with small livestock) at only one study site in the first year, but it was higher across all sites during the second year of monitoring. Dingo activity correlated with estimated dingo density at only two sites, suggesting differences in dingo behaviour and detection across the six study sites. This study provides experimental evidence that camera trap capture rate is not a reliable method for assessing variations in the population size of dingoes. These results have implications for monitoring outcomes of dingo control programs across Australia.

Land use and dingo baiting are correlated with the density of kangaroos in rangeland systems

Rangelands worldwide have been subject to broadscale modification, such as widespread predator control, introduction of permanent livestock water and altered vegetation to improve grazing. In Australia, these landscape changes have resulted in kangaroos (i.e. large macropods) populations increasing over the past 200 years. Kangaroos are a key contributor to total grazing pressure and in conjunction with livestock and feral herbivores have been linked to land degradation. We used 22 years of aerial survey data to investigate whether the density of 3 macropod species in the southern rangelands of Western Australia was associated with: (i) land use, including type of livestock, total livestock, density of feral goats, type of land tenure, and kangaroo commercial harvest effort; (ii) predator management, including permitted dingo control effort, estimated dingo abundance, and presence of the State Barrier Fence (a dingo exclusion fence); and (iii) environmental variables: ruggedness, rainfall, fractional cover, and total standing dry matter. Red kangaroos (Osphranter rufus) were most abundant in flat, open vegetation, on pastoral land, where area permitted for dingo control was high, and numbers were positively associated with antecedent rainfall with a 12-month delay. Western grey kangaroos (Macropus fuliginosus) were most abundant on flat, agricultural land, but less abundant in areas with high permitted dingo control. Euros (Osphranter robustus) were most abundant in rugged pastoral land with open vegetation, where permitted dingo control was high. While environmental variables are key drivers of landscape productivity and kangaroo populations, anthropogenic factors such as land use and permitted dingo control are strongly associated with kangaroo abundance.

Are canid pest ejectors an effective control tool for wild dogs in an arid rangeland environment?

Abstract Context Wild dogs are a significant pest species of livestock production and native wildlife in Australia. A suite of control tools is used to mitigate predation impacts. Baiting with sodium fluoroacetate is the most commonly used control tool in Australia; however, its effectiveness can be reduced by interference by non-target species, and in some contexts by microbial degradation of the toxin. Canid pest ejectors (CPEs) are a mechanical device with an attractant ‘lure head’ designed to eject a lethal toxin into the mouth of canids pulling on the lure head. A range of lure heads can be used to attract canids to pull, and trigger CPEs. Aims We aimed to determine whether uptake of CPEs by wild dogs in an arid rangeland environment could cause a decline in a wild dog population. We also aimed to determine whether there are particular lure heads that increase the rate of CPEs being triggered by wild dogs. Methods We deployed one hundred CPEs over four sessions of control across three properties in the southern rangelands of Western Australia from 2018 to 2020. Each session consisted of 2 months of CPE deployment with two different lure heads, totalling eight lure head types over the entire study. All CPEs were monitored using camera traps. Key results Wild dog density varied over the study period. In all four control sessions, a decrease in wild dog density was recorded (–46%, –5%, –13%, –38%). Wild dog activity events on camera and their interest in CPEs differed between sessions and lures (i.e. higher with scent-based lures). Non-target species did not interfere with CPEs significantly, despite a higher number of activity events by non-target species than wild dogs. Conclusions CPEs caused a reduction of 5–46% of wild dog density when deployed in the southern rangelands of Western Australia. Non-target interference was minimal when using CPEs for wild dog control. Implications Use of scent-based lures on felt lure heads is recommended for successful use of CPEs for wild dog control in arid rangeland environments. Future on-ground wild dog control should include CPEs as a complementary tool for the reduction of wild dog density.

Terrestrial mesopredators did not increase after top-predator removal in a large-scale experimental test of mesopredator release theory

Removal or loss of top-predators has been predicted to cause cascading negative effects for ecosystems, including mesopredator release. However, reliable evidence for these processes in terrestrial systems has been mixed and equivocal due, in large part, to the systemic and continued use of low-inference study designs to investigate this issue. Even previous large-scale manipulative experiments of strong inferential value have been limited by experimental design features (i.e. failure to prevent migration between treatments) that constrain possible inferences about the presence or absence of mesopredator release effects. Here, we build on these previous strong-inference experiments and report the outcomes of additional large-scale manipulative experiments to eradicate Australian dingoes from two fenced areas where dingo migration was restricted and where theory would predict an increase in extant European red foxes, feral cats and goannas. We demonstrate the removal and suppression of dingoes to undetectable levels over 4–5 years with no corresponding increases in mesopredator relative abundances, which remained low and stable throughout the experiment at both sites. We further demonstrate widespread absence of negative relationships between predators, indicating that the mechanism underpinning predicted mesopredator releases was not present. Our results are consistent with all previous large-scale manipulative experiments and long-term mensurative studies which collectively demonstrate that (1) dingoes do not suppress red foxes, feral cats or goannas at the population level, (2) repeated, temporary suppression of dingoes in open systems does not create mesopredator release effects, and (3) removal and sustained suppression of dingoes to undetectable levels in closed systems does not create mesopredator release effects either. Our experiments add to similar reports from North America, Asia, Europe and southern Africa which indicate that not only is there a widespread absence of reliable evidence for these processes, but there is also a large and continually growing body of experimental evidence of absence for these processes in many terrestrial systems. We conclude that although sympatric predators may interact negatively with each other on smaller spatiotemporal scales, that these negative interactions do not always scale-up to the population level, nor are they always strong enough to create mesopredator suppression or release effects.