Despite being numerous on the small, offshore islands, the quokka is classified as vulnerable. On the mainland, where it is threatened by introduced predatory species such as red foxes, cats, and dogs, it requires dense ground cover for refuge. Clearfell logging, agricultural development, and housing expansion have reduced their habitat, contributing to the decline of the species, as has the clearing and burning of the remaining swamplands. Moreover, quokkas usually have a litter size of one and successfully rear one young each year. Although they are constantly mating, usually one day after the young are born, the small litter size, along with the restricted space and threatening predators, contributes to the scarcity of the species on the mainland.