Enumerating a continental-scale threat: How many feral cats are in Australia?

The population size of feral cats in natural environments in Australia fluctuates between 1.4 and 5.6 million, depending on rainfall. An additional 0.7 million feral cats live in heavily modified environments like towns and intensive farms. The maps show the model predictions for cat density in natural environments across Australia during dry-average rainfall conditions (on the left) and after extensive rainfall events (on the right). They show that cat density is fairly uniform across the continent during average-dry conditions, but extensive rainfall events cause an increase in feral cat density in the inland of Australia. As predictors, the regression model includes mean annual rainfall, mean annual temperature, tree cover, ruggedness and fox presence/absence. For islands smaller than Tasmania, island area was also included as a predictor of density (small islands have higher cat densities). The dashed lines indicate the Tropic of Capricorn.