A study published in the research journal Biological Conservation says that feral cats now live in over 99.8 percent of Australia’s land area. The animals also cover nearly 80 percent of the area of the country’s islands.

Overall, the cat population is between 2.1 million and 6.3 million. The findings were from the study by more than 40 environmental scientists in Australia. The feral cat population threatens the country’s native wildlife, the researchers say. The team says that developing methods to control the population are needed.

“At the moment feral cats are undermining the efforts of conservation managers and threatened species recovery teams across Australia,” said Sarah Legge from The University of Queensland. “It is this difficulty which is pushing conservation managers into expensive, last resort conservation options like creating predator free fenced areas and establishing populations on predator-free islands.

Creating predator free fenced areas and establishing populations on predator-islands for wildlife are important for preventing species extinctions, the researchers say. However, these expensive methods are now enough. While the population of feral cats is less dense in Australia than in North America and Europe, the damage the animals do in the country is more devastating.

In the country’s heavily urbanized areas, feral cat population can be 30 times greater than in their natural environment. “Australia is the only continent on Earth other than Antarctica where the animals evolved without cats, which is a reason our wildlife is so vulnerable to them. This reinforces the need to cull feral cats humanely and effectively,” says Gregory Andrews, Australia’s Threatened Species Commissioner.

“With feral cats having already driven at least 20 Australian mammals to extinction, I’m so glad the Threatened Species Strategy is investing in science like this. This science reaffirms the importance of the ambitious targets to cull feral cats that I am implementing with the support of Minister Frydenberg under the Threatened Species Strategy.”