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) To characterize the riparian bird assemblage, and its variation, in a large area of northern Australia; (b) to examine the distinctiveness of this assemblage in relation to the broader landscape; (c) to consider the influence of disturbance on this assemblage; (d) to examine temporal variability in the riparian assemblage, and especially evidence for seasonal movements between riparian and non-riparian areas.Location c. 620,000 km 2 of the seasonal tropics of the Northern Territory, Australia.Methods (a) Synchronous sampling of birds in riparian and adjacent non-riparian areas at 100 sites stratified across 13 catchments and an extensive rainfall gradient. (b) Repeat visits to 13 of these sites at contrasting seasons. (c) Analysis of a larger distributional database to assess the relative occurrence of records in riparian areas relative to nonriparian areas.Results Species richness and the total abundance of birds was significantly greater in riparian zones than in matched non-riparian areas, especially where the riparian zones contained extensive cover of rain forest plants and Melaleuca . Similarity in bird species composition between riparian zones and adjacent non-riparian areas was generally low, and this distinction was greatest in lower reaches of the rivers and where the riparian zone contained no eucalypts. Bird species composition varied gradationally from riparian zones in high rainfall areas, through riparian zones in low rainfall areas and non-riparian zones in high rainfall areas, to non-riparian zones in low rainfall areas. Many species occurred widely across the riparian sites sampled. Of ninety-four species recorded from more than five sites, forty-five species were significantly more abundant in riparian zones than in matched non-riparian zones, whereas this pattern was reversed for only twelve species. There was little association between foraging group and preference for riparian zones. Species had highly idiosyncratic distributions across the riparian samples, with the most common trend being an association with mean annual rainfall. Many species were significantly more closely associated with riparian zones in lower rainfall areas than in higher rainfall areas. Indeed, many species typical of higher rainfall areas extended into lower rainfall areas only, or mainly, along riparian strips. There was some temporal fluidity in bird species composition of riparian zones, suggesting seasonal movements between riparian zones and the surrounding landscape. There was little evidence that disturbance was a major factor influencing the distribution of riparian birds, probably because other major geographical and environmental gradients probably dwarfed the influence of the relatively minor variation between samples in disturbance. Main conclusionsThe bird fauna of riparian areas is distinct from that of the surrounding savannas, and especially so in lower rainfall areas. Riparian vegetation allows many species to extend their distributions into lower rainfall areas. The riparian assemblage is l...

Bat surveys are frequently undertaken using ultrasonic detectors to determine the species present in an area on the basis of the identity of echolocation calls. We compared three techniques for using the Anabat II detector: the detector pointed along tracks (flyways) versus the detector pointed across tracks (non-flyways); recording output to audio cassette (analogue) versus direct recording to computer (digital); and active hand-held recording versus static automatic recording. In addition, we derived a species-accumulation curve from all-night Anabat recordings in the wet–dry tropics of the Northern Territory. We found no significant difference between flyway and non-flyway recordings; significantly more calls were identified from digital recordings; and significantly more species were detected using hand-held than static recordings. Species-accumulation analysis suggests that the minimum time required to achieve a satisfactory (80%) inventory of bat species at a site is during the three-hour period immediately after sunset. We use our findings to make recommendations for the design of bat surveys using the Anabat II detector.

Fires burn vast areas of the monsoonal savannas of northern Australia each year. This paper describes the contemporary fire regimes of two ecologically similar, relatively large national parks (Litchfield—1464 km2; Nitmiluk—2924 km2) in the Top End of the Northern Territory, over 8 and 9 years, respectively. Fire histories for both parks were derived from interpretation of LANDSAT TM imagery, supplemented with NOAA-AVHRR for cloudy periods at the end of the 7-month dry season (c. April–Oct). Data concerning seasonality, extent and frequency of burning were analysed with respect to digital coverages for the park as a whole, landscape units, vegetation types, infrastructure and tenure boundaries. Ground-truth data established that interpreted accuracy overall, for 2 assessment years, ranged between 82 and 91% for both parks. Over 50% of Litchfield and 40% of Nitmiluk was burnt on average over this period, with Litchfield being burnt substantially in the earlier, cooler, and moister, dry season, and Nitmiluk mostly in the parched late dry season, after August. On both parks the current frequency of burning in at least low open woodland / heath habitats is ecologically unsustainable. Both parks are prone to extensive fire incursions. The data support earlier regional assessments that the average fire return interval is around 2 years in at least some areas of northern Australia. Nevertheless, comparison of contemporary fire regimes operating in three major regional national parks shows distinct differences, particularly with respect to the extent and seasonality (hence intensity) of burning in relation to different landscape components. Management implications are considered in discussion.

Forty-seven 50 m × 50 m quadrats were sampled systematically for vertebrates at Litchfield National Park, northern Australia, in both 1995–96 and 2001–02. A total of 184 vertebrate species was recorded from this sampling, of which 92 species were recorded from five or more quadrats. There was substantial change in the reported species composition of these quadrats between these two periods: the mean Bray–Curtis index for similarity in species composition from the baseline to subsequent sampling of a quadrat was only 22.1 (for an index that varies from 0 for complete turnover in species to 100 for unchanged composition). For individual species, correlations across quadrats in the abundance scores from baseline to resampling varied from –0.12 to 0.85. Matched-pairs testing showed that there was significant change in abundance for 18 species from the baseline to repeat sampling, and significant increase in total bird species richness and total native mammal abundance, but significant decrease in reptile species richness. Fire history was recorded biannually for 40 of the 47 quadrats. Fire was very frequent, with quadrats being burnt in an average of 3.65 years of the six years between fauna samples. Three aspects of this fire history (total number of years of fires, number of fires in the late dry season, and interval from the last fire to the date of resampling) were related to change in the fauna composition of quadrats. Neither the similarity in species composition, nor change in richness or total abundance of all vertebrates or of the four taxonomic classes considered (frogs, reptiles, birds and mammals) were significantly correlated with these components of the fire history of sampled quadrats. This lack of association was possibly because the monitoring period was too short to show pronounced directional change, because the system was responding to many factors other than fire, because the variations in abundance were too large and the number of samples too small to detect true associations, or because fire histories preceding baseline sampling were not considered. The apparent instability of fauna species and communities in this system provides a considerable challenge for broad-brush (that is, vertebrate community–wide) monitoring. Power analysis demonstrated that, for most species, more than 1000 sample sites are needed to be 90% certain of detecting a 20% change in abundance, and with a 10% chance of accepting a Type I error. This level of sampling effort is commensurate with the current level of vertebrate sampling in this region. Broad-brush monitoring approaches such as described here are valuable, but need also to be complemented by more targetted monitoring for individual threatened species or species of particular management interest.