What do predator diets tell us about mammal declines in Kakadu National Park?

Abstract

Context Small- and medium-sized native mammals have suffered severe declines in much of northern Australia, including within protected areas such as Kakadu National Park. Several factors have been implicated in these declines but predation, particularly by feral cats (Felis catus), has been identified as potentially the most direct cause of decline for many species. Aims We evaluated how prey frequency changed in cat and dingo scats in Kakadu from the early 1980s to 2013–15, with this period spanning a severe decline in the small- and medium-sized mammal fauna. Methods Chi-square test of independence and Fisher’s exact test were used to compare prey frequencies between dingoes and cats, and among years to assess significance of temporal change. Key results Small-sized native mammals were the prey item occurring at the highest frequency in scats for both dingoes and cats in the 1980s. Prey content in dingo and cat scats differed in the 2010s with macropods predominating in the scats of dingoes, and medium-sized native mammals predominating in cat scats. The frequency of occurrence of small-sized native mammals declined in both dingo and cat scats between the 1980s and 2010 sampling periods, while the frequency of occurrence of medium-sized native mammals remained constant in dingo scats and increased in cat scats. Conclusions Small mammals were a major component of the diets of both dingoes and cats in Kakadu in the 1980s, when small mammals were much more abundant. Despite marked reduction from the 1980s to the 2010s in the capture rates of both small- and medium-sized native mammals, some species continue to persist in the diets of cats and dingoes at disproportionally high frequencies. Both predators continue to exert predatory pressure on mammal populations that have already experienced substantial declines. Implications Although predation by feral cats is a major threat to small- and medium-sized native mammals, dingoes may also play an important role in limiting their recovery. Disturbance from fire and grazing by introduced herbivores has been shown to augment predatory impacts of feral cats on native mammals. Predation more generally, not just by feral cats, may be exacerbated by these disturbance processes. Management programs that solely focus on mitigating the impact of feral cats to benefit threatened species may be inadequate in landscapes with other significant disturbance regimes and populations of predators.