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Modelling from the University of Melbourne helped Phillip Island Nature Parks decide how and when to scale back its fox eradication activities.
Phillip Island Nature Parks declared its fox eradication strategy a success in 2017. To make this decision, the organisation needed to balance the risks of declaring success too soon with the costs of continuous search and eradication efforts.
Modelling from University of Melbourne researchers helped to determine when the eradication efforts could be safely stopped in favour of ongoing monitoring.
Since 2017, animal populations that are vulnerable to fox predation – such as little penguins and other ground-nesting birds – have rebounded on the island. Only one fox has been detected, and it was found quickly using remote cameras and detection dogs.
In 2006, Phillip Island Nature Parks implemented an eradication strategy to remove all foxes from the island. Red foxes (Vulpes vulpes) were first spotted on Phillip Island in the early 1900s. Fox predation was a significant threat to native species such as little penguins.
After several years of eradication efforts, park managers needed help to determine when to declare their strategy a success. Foxes can be difficult to detect, so even if no evidence of foxes is found, they may still be on the island. Monitoring and removal cost around AU$160,000 a year in 2012. Park managers had to balance the cost of continuing their efforts unnecessarily – if eradication had been achieved – with the risks of ending them too soon. Stopping the fox control measures prematurely could allow populations to rebound, causing environmental damage and requiring many more years of management.
Developing the solution
Phillip Island Nature Parks had used five methods to find and remove foxes on the island: trapping, baiting, hunting, spotlighting and den searches. In the first few years of the eradication strategy, the goal was to substantially reduce the fox population. The strategy then moved to a ‘clean-up’ phase, where the last few remaining foxes were removed. Determining when to end the clean-up phase and begin the ‘post-eradication’ phase, which focused on preventing future fox incursions, proved difficult.
A team from Phillip Island Nature Parks led by Dr Duncan Sutherland worked with a University of Melbourne team led by Professor Michael McCarthy. Together, they developed a mathematical model to estimate the number of foxes on the island from 1986 to 2012 and to determine how effective the five control methods were in finding and removing foxes. Using this model, the researchers could estimate the number of foxes in the future depending on what control measures were used. They balanced this information with the costs of each control method, as well as the costs of repeating the eradication efforts if they were stopped prematurely.
Based on the modelling, Parks staff began using remote cameras and dog detection teams, which have a higher probability of finding foxes.
The researchers also used the model to determine how long Parks staff would need to maintain their intense control and monitoring efforts after the last sign of any fox in order to confidently declare that the species had been eradicated. The last fox was detected in August 2015, and Parks staff declared their eradication strategy a success in October 2017. Ongoing monitoring ensures that any newly arriving foxes are detected quickly and can be removed.
As a result of the fox eradication, it was safe to reintroduce eastern barred bandicoots to Phillip Island in 2017. This species, which is highly susceptible to fox predation, was previously classified by the Victorian Government as ‘extinct in the wild’. Thanks to the successful establishment of new populations on several islands in Victoria, the species has now been reclassified as ‘endangered’. Parks staff are also in the process of reintroducing and protecting other threatened species that struggle to persist in the presence of foxes.
Banner image: Phillip Island Nature Parks
ARC Discovery Project (DP110101499)
ARC Future Fellowship (FT100100923)
ARC Centre of Excellence for Environmental Decisions
Rout TM, Kirkwood R, Sutherland DR, Murphy S, McCarthy MA (2014) When to declare successful eradication of an invasive predator? Animal Conservation 17: 125–132. doi: 10.1111/acv.12065
Kirkwood R, Sutherland DR, Murphy S, Dann P (2014) Lessons from long-term predator control: a case study with the red fox. Wildlife Research 41: 222–232. doi: 10.1071/WR13196
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First published on 30 August 2022.
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