Do foxes suppress feral cats?

Foxes and feral cats are both well-known as threats to our native small mammals. But what happens to the population of one predator when the other is controlled? And what does this mean for our native small mammal populations?

One theory in ecology is that when a larger predator is suppressed, the ecological niche it occupies is filled by the next predator down the food chain – therefore pressure on shared prey species is maintained, or even enhanced.

Given foxes and cats prey on many of the same species, this ‘mesopredator release’ theory is a major concern for invasive predator control programs, such as fox-baiting, which do not also target feral cats.

With fox control being undertaken across the Otways since 2017 and in the Glenelg region since 2005, University of Melbourne PhD candidate, now Dr Matthew Rees, decided to investigate the impact of these fox control programs on feral cats.

By identifying individual cats in over 24,000 remote camera images and tracking their movements throughout the forests, Matt found cat densities tended to be higher with fox control. This effect appeared dependent on the level of fox suppression: feral cat density was highest where fox-baiting had occurred across broad scales for the longest.

He also noticed that cats may be adapting their daily rhythms to avoid foxes when they live in the same area; while both species are usually most active at night Matt found that cats became more active during the day when there were more foxes.

While Matt’s study found evidence that fox control may benefit feral cats, the net-outcome on native prey species remains unclear. While fox control has been effective for protecting larger threatened prey species (such as Long-nosed potoroos in the Glenelg region), Matt’s study highlights the need to also monitor species particularly susceptible to feral cats, such as native rodents and small marsupials.

One unexpected finding from the study was how many feral cats there were in the Otways compared to the Glenelg region to begin with, highlighting that density of feral cats in wet forests may have been underestimated in the past.

You can hear more from Matt in this recently recorded ARI Seminar: https://www.ari.vic.gov.au/seminars

Rees, M. W., Pascoe, J. H., Le Pla, M., Robley, A., Birnbaum, E. K., Wintle, B. A., & Hradsky, B. A. (2023). Mesopredator release among invasive predators: Controlling red foxes can increase feral cat density and alter their behaviour. Journal of Applied Ecology, 00, 1– 15. https://doi.org/10.1111/1365-2664.14402

Rees, M.W., Pascoe, J.H., Wintle, B., Le Pla, M., Birnbaum, E. and Hradsky, B. (2019).  Unexpectedly high densities of feral cats in a rugged temperate forest. Biological Conservation vol. 239. https://doi.org/10.1016/j.biocon.2019.108287