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Quantifying the cost‐effectiveness of alternative sampling methods is crucial for efficient biodiversity monitoring and detection of population trends. In this study, we compared the cost‐effectiveness of three novel sampling methods for detecting changes in koala (Phascolarctos cinereus) occupancy: thermal drones, passive acoustic recorders and camera trapping. Specifically, we fitted single‐season occupancy‐detection models to data recorded from 46 sites in eight bioregions of New South Wales, Australia, between 2018 and 2022. We explored the effect of weather variables on daily detection probability for each method and, using these estimates, calculated the statistical power to detect 30%, 50% and 80% declines in koala occupancy. We calculated power for different combinations of sites (1–200) and repeat surveys (2–40) and developed a cost model that found the cheapest survey design that achieved 80% power to detect change. On average, detectability of koalas was highest with one 24‐h period of acoustic surveys (0.32, 95% CI's: 0.26, 0.39) compared to a 25‐ha flight of drone surveys (0.28, 95% 0.15, 0.48) or a 24‐h period of camera trapping consisting of six cameras (0.019, 95% CI's: 0.014, 0.025). We found a negative quadratic relationship between detection probability and air temperature for all three methods. Our power and cost analysis suggested that 148 sites surveyed with acoustic recorders deployed for 14 days would be the cheapest method to sufficiently detect a 30% decline in occupancy with 80% power. We recommend passive acoustic recorders as the most efficient sampling method for monitoring koala occupancy compared to cameras or drones. Further comparative studies are needed to compare the relative effectiveness of these methods and others when the monitoring objective is to detect change in koala abundance over time. [ABSTRACT FROM AUTHOR]

Context: Management actions that suppress introduced predator densities can benefit the population recovery of native species. Nevertheless, ensuring that predator management produces measurable population-level benefits can be influenced by multiple factors affecting species detection. Monitoring designs using multiple survey methods may perform better than increasing sampling effort with single-method protocols. Aims: This study aimed to estimate individual and cumulative detection probabilities and site occupancy estimates from the use of five different monitoring methods to survey a native mesopredator, the lace monitor (Varanus varius). Second, we assessed the effect of lethal red fox (Vulpes vulpes) baiting on lace monitor detection probabilities and site occupancy estimates collected from each monitoring method. Methods: Multi-method sampling for Varanus varius occurred at 76 sites across lethal fox baited and non-baited habitats in East Gippsland, Victoria. Bayesian site occupancy models were used to estimate the effects of detection method and fox-baiting treatments on Varanus varius detection probability and site occupancy. Key results: Method-specific detection probabilities (P = 0.00–0.12) and site occupancy estimates (Ψ = 0–0.53) varied considerably among methods, but combinations of multi-method monitoring improved lace monitor detection probability (P = 0.11–0.18) and site occupancy (Ψ = 0.87 ± [0.66–0.93]−0.91 ± [0.76–0.97] mean ± [95% credible intervals]) above any single method. However, there was extreme heterogeneity in the size and direction of the introduced predator baiting effect on method-specific lace monitor detection. Three methods (box traps and two different visual search surveys) all indicated lace monitor detection probabilities increased in fox-baited sites. However, sand pads reported a decrease in lace monitor detection at fox-baited sites, whereas pipe traps obtained no detections. Conclusions: Combining detection data from all methods led to the inference of a positive fox-baiting effect, albeit with a smaller magnitude and better certainty than that estimated using a reduced method monitoring design, which had fewer detection data after excluding biased detection from sand pads. Implications: Using a multi-method monitoring approach improved lace monitor detection and reduced sampling effort. However, depending on sampling methodology, the management effects on lace monitors can change. Different wildlife sampling methods may provide various impressions of the extent of occurrence or occupancy of any given species, and influence views on the benefit or otherwise of management interventions. Therefore, multiple survey methods are expected to provide better insights into how native species respond to management actions. This study showed that different survey methods result in different inferences regarding management effects on lace monitors. Photograph by Tim Jessop. [ABSTRACT FROM AUTHOR]

Context: Small and medium-sized native mammals have declined precipitously across northern Australia. Feral cats have been implicated in causing declines and ongoing suppression of populations. Aims: The aim of the present study was to evaluate the response of small and medium-sized native mammal populations when cat predation was removed. Methods: A field experiment was conducted in a tropical savanna environment of northern Australia. Three experimental treatments were applied to six plots to compare and contrast responses of native mammals to predator exclusion and the additive effects of frequent fire. Plots were monitored regularly between 2013 and 2017. Key results: After 4 years of monitoring, no significant difference in capture rates of native mammals was detected between cat-accessible plots and those where they were excluded. Conclusions: There was no evidence of population recovery of native mammals in response to predator exclusion. There was some evidence that frequent burning, independent of cat exclusion, adversely affects native mammal diversity. Implications: Although predation by feral cats is a major threat to small and medium-sized native mammals, disturbance from fire, and grazing by introduced herbivores, have been shown to significantly impede native mammal population recovery in tropical savanna ecosystems. Management programs that solely focus on suppressing feral cat populations may be inadequate in ameliorating ongoing mammal declines in landscapes with other significant disturbance regimes. Feral cats have been implicated in driving declines of small native mammals in northern Australia, but it remains uncertain to what extent cat predation is primarily responsible for such declines, or for suppressing their recovery. We monitored population responses of native mammals to cat exclusion, and the potential interactive effects of fire. Native mammal populations did not increase in response to cat exclusion but are negatively impacted by frequent burning regimes. Photograph by the Northern Territory Government. [ABSTRACT FROM AUTHOR]

Keywords: Bathurst Island; feral cat; fire management; grazing; herbivores; Melville Island; native mammals; northern Australia; population density. For example, there has been zero feral cat detections from around 12 600 camera-trap nights conducted on Bathurst Island since 2014; this is despite stray cats being present in and around the community of Wurrumiyanga ([11]) and feral cats being occasionally sighted away from communities (C. Kerinauia, pers. comm.). Although cat activity patterns and movement could indeed vary between these islands, the most plausible explanation, is that cat density is much lower on Bathurst Island compared with Melville Island. The session-specific model indicated that feral cat density at Pickertaramoor (0.21 cats km SP -2 sp ) was more than double that of Cache Point (0.09 cats km SP -2 sp ), however confidence intervals overlapped substantially (Table 2). [Extracted from the article]