Lessons from long-term predator control: a case study with the red fox

Context. Predator-control aims to reduce an impact on prey species, but efficacy of long-term control is rarely assessed and the reductions achieved are rarely quantified. Aims. We evaluated the changing efficacy of a 58-year-long campaign against red foxes (Vulpes vulpes) on Phillip Island, a 100-km(2) inhabited island connected to the Australian mainland via a bridge. The campaign aimed to eliminate the impact of foxes on ground-nesting birds, particularly little penguins (Eudyptula minor). Methods. We monitored the success rate of each fox-control technique employed, the level of effort invested if available, demographics of killed foxes, the numbers of penguins killed by foxes and penguin population size. Key results. The campaign began as a bounty system that ran for 30 years and was ineffective. It transitioned into a coordinated, although localised, control program from 1980 to 2005 that invested considerable effort, but relied on subjective assessments of success. Early during the control period, baiting was abandoned for less effective methods that were thought to pose fewer risks, were more enjoyable and produced carcasses, a tangible result. Control was aided by a high level of public awareness, by restricted fox immigration, and by a clear, achievable and measurable target, namely, to prevent little penguin predation by foxes. Carcasses did prove valuable for research, revealing the genetic structure and shifts in fox demographics. The failure of the program was evident after scientific evaluation of fox population size and ongoing fox impacts. In 2006, the campaign evolved into an eradication attempt, adopting regular island-wide baiting, and since then, has achieved effective knock-down of foxes and negligible predation on penguins. Conclusions. Effective predator control was achieved only after employing a dedicated team and implementing broad-scale baiting. Abandoning widespread baiting potentially delayed effective control for 25 years. Furthermore, both predator and prey populations should be monitored concurrently because the relationship between predator abundance and impact on prey species is not necessarily density dependent. Implications. Critical to adopting the best management strategy is evaluating the efficacy of different methods independently of personal and public biases and having personnel dedicated solely to the task.