This article provides a context to, attempts an explanation for, and proposes a response to the recent demonstration of rapid and severe decline of the native mammal fauna of Kakadu National Park. This decline is consistent with, but might be more accentuated than, declines reported elsewhere in northern Australia; however, such a comparison is constrained by the sparse information base across this region. Disconcertingly, the decline has similarities with the earlier phase of mammal extinctions that occurred elsewhere in Australia. We considered four proximate factors (individually or interactively) that might be driving the observed decline: habitat change, predation (by feral cats), poisoning (by invading cane toads), and novel disease. No single factor readily explains the current decline. The current rapid decline of mammals in Kakadu National Park and northern Australia suggests that the fate of biodiversity globally might be even bleaker than evident in recent reviews, and that the establishment of conservation reserves alone is insufficient to maintain biodiversity. This latter conclusion is not new; but the results reported here further stress the need to manage reserves far more intensively, purposefully, and effectively, and to audit regularly their biodiversity conservation performance.

Aim To compare fire behaviour and fire management practice at a site managed continuously by traditional Aboriginal owners with other sites in tropical northern Australia, including the nearby Kakadu National Park, and relate those observations to indicators of landscape condition. Location Dukaladjarranj, a clan estate in north‐central Arnhem Land, in the seasonal tropics of northern Australia. The site abuts a vast sandstone plateau that is an internationally recognized centre of plant and animal biodiversity. Methods Ecological assessments included: (1) mapping of the resource base of the estate from both traditional and ecological perspectives; (2) aerial survey of the extent of burning, distribution of the fire‐sensitive native pine Callitris intratropica, rock habitats, and a range of macropod and other fauna resources; (3) fauna inventory; (4) detailed ecological assessment of the status of fire‐sensitive vegetation; and (5) empirical assessment of the intensities of experimental fires. Ethnographic information concerning traditional fire management practice was documented in interviews with senior custodians. Results Experimental fires lit during the study were of low intensity compared with late dry season fires reported elsewhere, despite weather conditions favouring rapid combustion. In contrast to other parts of the savanna, fuel loads comprised mostly leaf litter and little grass. We found that (i) a large proportion of the estate had been burned during the year of the study (ii) burned sites attracted important animal food resources such as large macropods (iii) important plant foods remained abundant (iv) well represented in the landscape were fire sensitive vegetation types (e.g. Callitris intratropica Baker & Smith woodlands) and slow growing sandstone ‘heath’ typically dominated by myrtaceaous and proteaceous shrubs (v) diversity of vertebrate fauna was high, including rare or range‐restricted species (vi) exotic plants were all but absent. Traditional practice includes regular, smaller fires, lit throughout the year, and cooperation with neighbouring clans in planning and implementing burning regimes. Main conclusions We attribute the ecological integrity of the site to continued human occupation and maintenance of traditional fire management practice, which suppresses otherwise abundant annual grasses (Sorghum spp.) and limits accumulation of fuels in perennial grasses (Triodia spp.) or other litter. Suppression of fuels and coordination of fire use combine to greatly reduce wildfire risk and to produce and maintain diverse habitats. Aboriginal people derive clear economic benefits from this style of management, as evidenced by abundant and diverse animal and plant foods. However, the motives for the Aboriginal management system are complex and include the fulfillment of social and religious needs, a factor that remains important to Aboriginal people despite the rapid and ongoing transformation of their traditional lifestyles. The implication of this study is that the maintenance of the biodiv...

Context. Australia has a lamentable history of mammal extinctions. Until recently, the mammal fauna of northern Australia was presumed to have been spared such loss, and to be relatively intact and stable. However, several recent studies have suggested that this mammal fauna may be undergoing some decline, so a targeted monitoring program was established in northern Australia’s largest and best-resourced conservation reserve. Aims. The present study aims to detect change in the native small-mammal fauna of Kakadu National Park, in the monsoonal tropics of northern Australia, over the period of 1996–2009, through an extensive monitoring program, and to consider factors that may have contributed to any observed change. Methods. The small-mammal fauna was sampled in a consistent manner across a set of plots established to represent the environmental variation and fire regimes of Kakadu. Fifteen plots were sampled three times, 121 plots sampled twice and 39 plots once. Resampling was typically at 5-yearly intervals. Analysis used regression (of abundance against date), and Wilcoxon matched-pairs tests to assess change. For resampled plots, change in abundance of mammals was related to fire frequency in the between-sampling period. Key results. A total of 25 small mammal species was recorded. Plot-level species richness and total abundance decreased significantly, by 54% and 71%, respectively, over the course of the study. The abundance of 10 species declined significantly, whereas no species increased in abundance significantly. The number of ‘empty’ plots increased from 13% in 1996 to 55% in 2009. For 136 plots sampled in 2001–04 and again in 2007–09, species richness declined by 65% and the total number of individuals declined by 75%. Across plots, the extent of decline increased with increasing frequency of fire. The most marked declines were for northern quoll, Dasyurus hallucatus, fawn antechinus, Antechinus bellus, northern brown bandicoot, Isoodon macrourus, common brushtail possum, Trichosurus vulpecula, and pale field-rat, Rattus tunneyi. Conclusions. The native mammal fauna of Kakadu National Park is in rapid and severe decline. The cause(s) of this decline are not entirely clear, and may vary among species. The most plausible causes are too frequent fire, predation by feral cats and invasion by cane toads (affecting particularly one native mammal species). Implications. The present study has demonstrated a major decline in a key conservation reserve, suggesting that the mammal fauna of northern Australia may now be undergoing a decline comparable to the losses previously occurring elsewhere in Australia. These results suggest that there is a major and urgent conservation imperative to more precisely identify, and more effectively manage, the threats to this mammal fauna.

Aim A third of all modern (after 1500) mammal extinctions (24/77) are Australian species. These extinctions have been restricted to southern Australia, predominantly in species of ‘critical weight range’ (35–5500 g) in drier climate zones. Introduced red foxes (Vulpes vulpes) that prey on species in this range are often blamed. A new wave of declines is now affecting a globally significant proportion of marsupial species (19 species) in the fox‐free northern tropics. We aim to test plausible causes of recent declines in range and determine if mechanisms differ between current tropical declines and past declines, which were in southern (non‐tropical) regions. Location Australian continent Methods We used multiple regression and random forest models to analyse traits that were associated with declines in species range, and compare variables associated with past extinctions in the southern zones with current tropical (northern) declines. Results The same two key variables, body mass and habitat structure, were associated with proportion‐of‐decline in range throughout the continent, but the form of relationships differs with latitude. In the south, medium‐sized species in open habitats of lower rainfall were most likely to decline. In the tropics, small species that occupy open vegetation with moderate rainfall (savanna) are now experiencing the most severe declines. Throughout the continent, large‐bodied species and those in structurally complex habitats (rainforest) are secure. Main conclusions Our results indicate that there is no mid‐sized ‘critical weight range’ in the north. Because foxes are absent from the tropics, we suggest that northern Australian marsupial declines are associated with predation by feral cats (Felis catus) exacerbated by reduced ground level vegetation in non‐rainforest habitats. To test this, we recommend experiments to remove cats from some locations where tropical mammals are threatened. Our results show that comparative analysis can help to diagnose potential causes of multi‐species decline.