Trappability of introduced and native rodents in different trap types in coastal forests of south-eastern Australia

Trapping is an invaluable tool for estimating community composition and population size and structure of mammals. Bias in the relative contribution of species to a community and the age and sex structure of populations can occur where the traps used do not equally trap all species, sexes or cohorts. The aim of this study was to compare the efficiency of enclosed Elliott traps and open wire cage traps in trapping the invasive black rat, Rattus rattus, and the native rodent, Rattus fuscipes. Both trap types were suitable for trapping R. fuscipes and there was no apparent bias in capture of sex and age classes. In contrast, black rats were considerably more trappable in cage traps. Juveniles were more readily trapped in Elliott traps than adults, but were still considerably undersampled where only Elliott traps were used. These findings have important implications for sampling invasive rodents in Australian forests where Elliott traps are commonly used to census small mammals. Only using Elliott traps will underestimate density, distribution and impacts of R. rattus in native habitats. Cage traps or a combination of traps are recommended for reliably trapping black rats and obtaining representative data on presence, abundance and distribution.