Many mammals in Australia's tropical north are in severe decline, yet understanding of the drivers of this decline is remarkably limited. Recently, Fisher et al. (Global Ecology and Biogeography, 2014, 23, 181−190) examined the traits that are associated with declining marsupial species in northern Australia. They concluded that, in this region, declines are most pronounced in the smallest species (those with the lowest body mass). This is in strong contrast to the significant declines that occurred earlier in central and southern Australia before the mid 20th century, which were most pronounced in medium-sized species, the so-called ‘critical weight range’ (35−5500 g). Here we show that Fisher et al. have misinterpreted their dataset; in northern Australia, the pattern of mammal decline in relation to body mass is remarkably similar to that in central and southern Australia, with mammal decline strongly concentrated in the critical weight range, suggesting fundamentally similar drivers between north and south.