The decline of small to medium-sized (35-5500 g) non-flying mammals in northern Australia is one of our most urgent conservation issues. In Kakadu National Park, the site with the most substantial long-term evidence base, populations of many species have collapsed since the 1970s. This pattern has repeated across the north, and only a few high-rainfall regions retain a largely-intact assemblage of mammals.
The threats are uncertain, although there is evidence that feral cats (present in the region since the 19th Century) and altered fire regimes play key roles. Cats may act synergistically with high-intensity fires, which remove ground-level vegetation cover, increasing mammals’ exposure to predation. Recent work shows cats: (1) can rapidly extirpate native rodents in experimental trials; (2) prefer habitats burnt by high-intensity fires, where they hunt more efficiently. There is evidence that frequencies of high-intensity fires increased with the loss of customary Indigenous fire management. Cattle may have similar impacts to fire, removing groundcover and facilitating predation. Other potential drivers, which have received little attention, include: (1) disease; (2) fire-driven reductions in habitat quality (e.g. reduced understorey diversity, abundance of hollow trees and logs).
Research to resolve the threats is key to formulating an effective management response. However, high rates of decline demand immediate attempts to sustain remnant populations. Management trials could focus on: (1) intensive fire management (to maintain long-unburnt habitat, prevent high-intensity fires); (2) cat suppression; (3) improving habitat quality (e.g. removing cattle, providing nest boxes). Many northern islands have retained mammal species that have declined drastically on the mainland, and also offer potential translocation sites. Biosecurity for these islands is critical, and, if cats are present, eradication should be considered.