Field assessment of the risk of feral cat baits to nontarget species in eastern Australia

Feral cats (Felis catus) pose a significant threat to wildlife, agriculture, and human health through predation, disease transmission, and competition with native animals. Controlling feral cats and their impacts, however, is challenging. New and emerging 1080-based feral cat baits have shown promising results in western and central Australia; however, the safety of these new baits for nontarget species in eastern Australia, where many native animals are more sensitive to compound 1080 (sodium fluoroacetate) than their western conspecifics, has not been assessed. We investigated the uptake of 499 toxic Eradicat^® baits by nontarget animals across five different eastern Australian environs and the uptake of nontoxic Eradicat and Hisstory^® baits at an additional two sites. Using field-based observations of species eating or removing baits, we determined that 13 nontarget species (eight mammals, four birds, and one reptile) were at high risk of individual mortality, with individuals of 11 of those 13 species (seven mammals, four birds) observed consuming enough toxic Eradicat in a single visit to ingest a lethal dose of 1080. Feral cats (the target species) consumed only 3.1% of monitored baits, which was only 52% of the 31 baits they encountered. We recommend undertaking targeted population monitoring of species identified at high risk of individual mortality, to determine whether Eradicat baits present a population-level risk to these species. Our findings suggest that the small-sized Eradicat baits present a greater risk to nontarget species in eastern Australia than the larger traditional 1080-based meat baits used for the control of wild dogs and foxes. Our study highlights the importance of performing risk assessments for different bait types, even when the same toxin is used, and of performing site-specific nontarget risk assessments of new baits such as Eradicat to assist developing guidelines for their safe and effective use in different environs. Integr Environ Assess Manag 2022;18:224-244. © 2021 State of Queensland. Integrated Environmental Assessment and Management © 2021 SETAC.

Measuring, evaluating and improving the effectiveness of invasive predator control programs: Feral cat baiting as a case study

Reducing the impacts of invasive predators is a key objective for conservation managers, livestock producers and human health agencies globally. The efficacy of invasive predator control programs, however, is highly variable. To improve control efficacy, managers require a fundamental understanding of the factors that contribute to the success or failure of a control program. Using a predator baiting program as a case study, we measured the efficacy of baiting as a control tool to significantly reduce feral cat (Felis catus) populations. We used camera traps and cat-borne GPS collars to monitor changes in feral cat populations at a baited site and an unbaited site, using a Before-After, Control-Impact (BACI) design. We also identified five key elements required for a successful baiting program (bait encounter rate, availability, attractiveness, palatability and lethality) and simultaneously measured these to identify areas for potential improvement. Baiting was ineffective at reducing feral cat populations; collared cat mortality was only 11% (1/9), with camera traps revealing negligible reductions in the number of cat detection events (9%), naïve occupancy (15%), and no significant change in the relative abundance of feral cats (F_1,54 = 0.8641, P = 0.357). Several factors contributed to the poor control efficacy. Bait encounter rates were low, with cats active along tracks (where baits were laid) < 4% of the time. Cats encountered only 14% (7/50) of monitored baits, but none were eaten. Initially, baits appeared attractive to cats; however meat ants and desiccation rapidly decreased bait palatability. Bait availability to cats declined rapidly, with 36% of monitored baits (18/50) removed by non-target species within the first 48 h. The mortality of one collared cat and chemical assays confirmed that, on average, each bait contained sufficient 1080 to kill a large (>5 kg) feral cat. Our findings suggest that altering bait deployment patterns, increasing bait densities and improving bait palatability could potentially improve the efficacy of baiting programs to reduce feral cat populations. Our study provides a framework to measure and evaluate the key elements that contribute to efficacy of pest control programs, and to identify opportunities for improving outcomes of future control programs.

Population dynamics of house mice in Queensland grain-growing areas

Context Irregular plagues of house mice cause high production losses in grain crops in Australia. If plagues can be forecast through broad-scale monitoring or model-based prediction, then mice can be proactively controlled by poison baiting. Aims To predict mouse plagues in grain crops in Queensland and assess the value of broad-scale monitoring. Methods Regular trapping of mice at the same sites on the Darling Downs in southern Queensland has been undertaken since 1974. This provides an index of abundance over time that can be related to rainfall, crop yield, winter temperature and past mouse abundance. Other sites have been trapped over a shorter time period elsewhere on the Darling Downs and in central Queensland, allowing a comparison of mouse population dynamics and cross-validation of models predicting mouse abundance. Key results On the regularly trapped 32-km transect on the Darling Downs, damaging mouse densities occur in 50% of years and a plague in 25% of years, with no detectable increase in mean monthly mouse abundance over the past 35 years. High mouse abundance on this transect is not consistently matched by high abundance in the broader area. Annual maximum mouse abundance in autumn–winter can be predicted (R2 = 57%) from spring mouse abundance and autumn–winter rainfall in the previous year. In central Queensland, mouse dynamics contrast with those on the Darling Downs and lack the distinct annual cycle, with peak abundance occurring in any month outside early spring. On average, damaging mouse densities occur in 1 in 3 years and a plague occurs in 1 in 7 years. The dynamics of mouse populations on two transects ~70 km apart were rarely synchronous. Autumn–winter rainfall can indicate mouse abundance in some seasons (R2 = ~52%). Conclusion Early warning of mouse plague formation in Queensland grain crops from regional models should trigger farm-based monitoring. This can be incorporated with rainfall into a simple model predicting future abundance that will determine any need for mouse control. Implications A model-based warning of a possible mouse plague can highlight the need for local monitoring of mouse activity, which in turn could trigger poison baiting to prevent further mouse build-up.