Millions of feral cats roam Australia, where they grow fat and sleek on a diet that includes large helpings of native mammals. Now, Brett Murphy at Charles Darwin University in Darwin, Australia, and a large cast of co-authors have combined estimates of cat prevalence with surveys of mammalian remains in cat poo and stomachs to estimate the total number of their prey.

According to the scientists’ data, feral cats living in natural landscapes kill 815 million mammals each year, of which 56% are native species. These numbers are considerably larger than the at least 2.1 million native mammals killed by land clearing each year.

The researchers note that pet cats, even those that are amply provided for at home, still kill large numbers of mammals — about 180 million annually. These are predominately non-native species found in urban and suburban areas.

A higher proportion of native-mammal remains was found in cat scats from northern Australia than in poos from the more urbanized south, where native creatures have fared poorly.