Long-term trends in native mammal capture rates in a jarrah forest in south-western Australia

Abstract

Summary The south-western Australian forests and woodlands are important refugia for many species of native mammals that were once widespread across the continent. In the late 1960s, the Perup jarrah forest was identified as being particularly rich in native mammals. Following light selection logging in the 1960s and early 1970s, the forest was primarily managed for the conservation of fauna in recognition of its outstanding conservation value. Detailed fauna studies commenced in 1974 following a preliminary survey and trapping in 1971. Mammal trapping has continued in the Perup forest for twenty-six years, making that forest the site of one of the longest mammal monitoring studies in Australia. Long-term trends in the capture rates of four species, Bettongia penicillata (woylie), Dasyurus geoffroii (chuditch), Isoodon obesulus (quenda) and Trichosurus vulpecula (common brushtail possum), reveal that capture rates, which could be interpreted as mammal abundance, coincide with the level of effort to control the introduced fox (Vulpes vulpes). In the absence of fox control during the early 1970s capture rates of native mammals were less than 12% (i.e. fewer than 12% of traps set caught an animal overnight). In the northern part of Perup forest the woylie was presumed extinct as none was trapped or observed. Between 1977 and 1998, with ongoing fox control, capture rates increased to more than 70%. The woylie showed the greatest increase in capture rate and was the most widespread and commonly caught animal. The capture rates of the other species also increased, but more than 80% of mammals captured were woylies. The high abundance of woylies in recent times has compromised the monitoring protocol, with virtually all traps set catching or being tampered with by woylies, rendering them unavailable to other less-abundant species. A new monitoring protocol is suggested to accommodate the high population density of native mammals.