J. C. Z. Woinarski

Very large area requirements for frugivorous birds in monsoon rainforests of the Northern Territory, Australia

Frugivorous birds in the Northern Territory, Australia move among patches of monsoonal rainforest and require many patches to maintain their populations. Using bird survey data from 149 rainforest patches and GIS coverage of all of the ca. 15,000 patches in the Northern Territory, we analyzed the relationship between the occurrence of six frugivorous bird species, patch area, and various measures of patch isolation. Rose-crowned fruit-doves (Ptilinopus regina) and pied imperial-pigeons (Ducula bicolor) exhibited strong relationships with a particular isolation measure: the percentage of rainforest within 50 km of the study patch. This result was not a statistical artifact of correlations between the measure and floristic or geographical variation between patches. Yellow orioles (Oriolus flavicintus) and common koels (Eudynamys scolopacea) were also influenced by this isolation measure, but various other factors (e.g. patch size and proximity to coastal areas) were more significant. Figbirds (Sphecotheres viridis) and great bowerbirds (Chlamydera nuchalis) were not particularly affected by patch isolation, and are probably not strongly dependent on rainforest. These relationships can be used to predict the consequence of destroying patches: for example, if half of the rainforest patches in the Darwin region were destroyed, our models predict that 80% of the pigeons and 90% of the doves would disappear. A threshold value was apparent for the pigeon, dove, and koel, suggesting that a critical degree of connectedness between patches over a very large area (32 km2 of rainforest in a 7900 km2 circle) is necessary to maintain these species.

The conservation status of rodents in the monsoonal tropics of the Northern Territory

The rodent fauna of the monsoonal tropics of the Northern Territory comprises 23 native species and two introduced species. Three species (Zyzomys maini, Z. palatalis and Pseudomys calabyi) are endemic to the area, and four species (Pseudomys hermannsburgensis, P. desertor, P. johnsoni and Notomys alexis) enter the area only on its southern (arid) fringe. The rodent fauna is closely related to that of the Kimberley, Western Australia. Distribution maps for all species are given. One species (Z. palatalis) has an extremely restricted range and is regarded as critically endangered. The lack of information on the distribution and abundance of rodents in general in this area is evident in the national classification of five of its species (Xeromys myoides, Mesembriomys macrurus, Notomys aquilo, Pseudomys desertor and Pseudomys johnsoni) as Insufficiently Known. The two introduced rodents (Mus domesticus and Rattus rattus) are virtually restricted to urban and highly modified areas, although R. rattus also occurs on one uninhabited island. In contrast to that of much of the rest of Australia, this rodent fauna has apparently retained its full complement of species since European colonisation. This enduring legacy is attributable largely to the relatively limited modification of its environments. However, three species (Mesembriomys macrurus, Rattus tunneyi and Conilurus penicillatus) appear to be declining. The pattern of decline in these species, and in the mammal fauna generally, is obscured by the very limited historical data. However, declines appear most pronounced in the cattle country of the Victoria River District and Gulf regions. Priorities for the management of this rodent fauna include survey of poorly known areas, survey for poorly known species, monitoring of rodent communities, and landscape-wide management of the three pervasive processes with probably greatest impacts – fire, grazing and feral predators.

Distributional patterning of mammals on the Wessel and English Company Islands, Arnhem Land, Northern Territory, Australia

Eighteen non-marine mammal species (including seven species of bats) were recorded from a total of 49 islands in the Wessel and English Company island chains off north-eastern Arnhem Land, Northern Territory. Most individual species were restricted to, or had higher incidence on, larger islands, and species richness as a whole increased as island size increased. The most notable exception was the semi-aquatic Hydromys chrysogaster, which occurred relatively equitably across island sizes; this species, two bat species and the macropod Petrogale brachyotis were recorded from islands smaller than 10 ha. However, the variation between islands in the number of native terrestrial mammal species was not best predicted by island size, but rather by a combination of sampling effort and altitude (which explained 64% of the deviance in species richness), or altitude and distance to larger land mass (explaining 63% of deviance). Richness–area patterns for individual islands in these chains were reasonably consistent with those of other islands sampled in northern Australia. However, the fauna of the Wessel and English Company groups as a whole was less rich than that of the Pellew and Kimberley islands, and individual islands appeared to have lower species richness than comparable mainland areas. Species that were notably absent or that were recorded from relatively few islands include large macropods, Tachyglossus aculeatus, Antechinus bellus, Phascogale tapoatafa, Sminthopsis spp., Mesembriomys gouldii, Rattus colletti, Leggadina lakedownensis and Pseudomys calabyi. Some of these species may be absent through lack of suitable habitat; others have presumably disappeared since isolation, possibly due to Aboriginal hunting. Richness at the quadrat (50 × 50 m) scale was generally very low. Habitat relationships are described for the 7 species recorded from more than 5 quadrats. At a quadrat-scale, the richness of native mammals was greater on islands larger than 1000 ha than on islands smaller than 1000 ha. Quadrat-scale species richness varied significantly among the islands sampled by the most quadrats (even when the comparison was restricted to either of the two most extensive vegetation types), but this variation was not closely related to either area or altitude. The two most frequently recorded species, the rodents Melomys burtoni and Zyzomys argurus, showed distinct habitat segregation on islands where both were present, but tended to expand their habitat range on islands where only one of the species occurred. The most notable conservation feature of the mammal fauna of the Wessel and English Company Islands is the occurrence of the golden bandicoot, Isoodon auratus, a vulnerable species apparently now extinct on the Northern Territory mainland. Four feral animal species (Rattus rattus, Canis familiaris, Bubalus bubalis and Capra hircus) were recorded from a total of 6 islands.

Seasonal habitat use by flying‐foxes, Pteropus alecto and P. scapulatus (Megachiroptera), in monsoonal Australia

Distributions of flying-fox (Pteropus alecto and P. scapulatus) were examined in relation to use of habitat in the essentially natural landscape of northern Australia. There were differences between the species in terms of the vegetation used for roosting and foraging, which were related to the reproductive cycle and seasonal variation in temperature, rainfall and the availability of preferred foods. Important habitats of P. alecto varied seasonally and included floodplain, mangrove, monsoon rainforest, Melaleuca open-forest, and Eucalyptus miniata/E. tetrodonta open-forest and woodland. The minimum scale at which conservation of P. alecto should be attempted is in the order of 5000 km2, based on seasonal patterns of habitat use. The size of this area will make conservation via traditional reserves difficult and conservation of important habitats outside reserves will be needed. Habitats protected for the benefit of P. alecto will also benefit P. scapulatus but because P. scapulatus is more mobile, displays greater yearly variation in distribution and is less well understood than P. alecto, appropriate conservation actions are less certain.

Historical changes in the bird fauna at Coomooboolaroo, northeastern Australia, from the early years of pastoral settlement (1873) to 1999

Abstract Across most of northern Australia, the historical record is generally insufficient to serve as a baseline for interpreting the impacts of European settlement on fauna. A notable exception is the pastoral property Coomoobolaroo (454 km2) in central Queensland, where the ornithologist Charles Barnard maintained a detailed record of bird fauna from 1873 to 1933. We re-surveyed the property in 1999, and collated other information on its current avifauna, giving 242 species in total recorded over the period 1873–1999 (of which we had sufficient information to ascribe trends to 200 species). The bird fauna of Coomooboolaroo has undergone substantial change, across both of the periods 1873–1933 and 1934–1999. From 1873 to 1999, 45% of species declined or were lost from the property, compared with 13% of species that either colonised the property or increased. Most of the latter are widespread species or those known to benefit from clearing and land development. This extent of change appears at least as high as that reported for most comparable studies elsewhere in Australia, despite these being conducted at sites that have been subjected to superficially greater environmental degradation. The greatest rates of loss occurred among birds associated with softwood scrub (dry rainforest), grasslands and swamps. Smaller species were more susceptible to decline, but change in status was not significantly associated with foraging style nor different between residents and migrants. Many of the species that have declined at Coomooboolaroo have also declined in many other geographic regions, habitats and land-uses. Change in status at this property can be attributed to diverse factors, including changes in predation pressures; environmental change due to altered fire regimes and/or grazing by livestock; and vegetation clearance at both property and regional scales. The multiplicity and complex interrelationships of such factors renders it difficult to predict assemblage-level change.

Population and habitat characteristics of the golden bandicoot (Isoodon auratus) on Marchinbar Island, Northern Territory.

The presence of the golden bandicoot (Isoodon auratus) on Marchinbar Island off north-eastern Arhemland, Northern Territory, was confirmed by means of morphological features, hair characteristics and allozyme electrophoresis. Evidence of I. auratus was found at most points sampled along the 50-km length of Marchinbar Island. The species showed a strong habitat preference for low heath or shrubland on sand or sandstone, a combination that covers some 70% or 140 km2 of the island. No sign was found in the remaining forest/thicket or strand/Casuarina habitat. No major changes occurred in the distribution of the species between seasons, and individuals maintained overlapping home ranges of similar size, about 10-35 ha. Considerable variation occurred in the characteristics of sites used for daytime shelter, including rocky shelves, shrubs and Triodia hummocks. Different shelter sites were frequently occupied on consecutive days. Foraging sites were sparsely vegetated and diet consisted mainly of a broad range of invertebrates. It is likely that the rocky habitat of Marchinbar Island is sufficiently dissected to ensure the availability of suitable habitat without the necessity of a managed fire regime. The bandicoot population on Marchinbar Island has at least two terrestrial predators, wild dogs (Canis familiaris) and carpet pythons (Morelia spilota). The current predation pressure is not considered to threaten the existence of the bandicoots on the island; however, the addition of another predator species (e.g. the feral cat) may create unacceptable conditions.

Rodents of the arid Northern Territory: conservation status and distribution

At the time of European entry, 18 species of rodent occurred in the arid zone of the Northern Territory, including two endemic species, Zyzomys pedunculatus and Pseudomys johnsoni. The tally is somewhat inflated, as the arid Northern Territory is on the margins of the distribution for seven of these species. The historical record for this fauna is generally reasonably good, due to important collections around the end of the nineteenth century, some landmark studies (notably by H.H. Finlayson) earlier this century, documentation of Aboriginal knowledge, and the recent discovery and analysis of fossil and sub-fossil deposits. Notwithstanding this good historical baseline, recent research has added three native species to the fauna, and re-discovered one species, Z. pedunculatus, earlier feared extinct. Over the last 200 years, four species (Leporillus apicalis, Notomys amplus, N. longicaudatus and Pseudomys fieldi) have disappeared, and a further five species (N. cervinus, N. fuscus, P. australis, Rattus tunneyi and Z. pedunculatus) have declined considerably, with several of these perhaps no longer present in the area. The decline in this rodent fauna is matched, or indeed surpassed, by declines in the arid-zone bandicoots, small macropods and large dasyurids. But notably the small dasyurids have generally suffered few declines. There has been differential decline within the rodent fauna, with declines mainly affecting larger species, species with the most idiosyncratic diets, and species occurring mainly in tussock grasslands and gibber plains. The main conservation and management actions required to safeguard what is left of this fauna are carefully targetted studies examining the effect of threatening processes, complemented by landscape-wide amelioration of these threats. Additional autecological studies are also needed for some species, and some exceptionally poorly known areas should be surveyed. Current work examining the distribution, ecology and management requirements of the endangered Z. pedunculatus is a major priority.

Hollow use by vertebrates in the Top End of the Northern Territory

Information on forest use and dependence on tree hollows was collated for vertebrates in the Top End of the Northern Territory. The proportion of the total fauna that used hollows was 40% for mamma...

Vegetation of the Wessel and English Company Islands, North-eastern Arnhem Land, Northern Territory, Australia

Vegetation patterning is described for two neighbouring continental island chains off Arnhem Land, Australia. A total of 684 species was recorded from 57 islands, with reasonably comprehensive lists for 36 of these islands. Almost 90% of the deviance in plant species richness was associated with island size. The richness of plants dispersed by sea and/or vertebrates was proportionally greater on small islands; that of relatively poor dispersers was greater on larger islands. Twelve vegetation communities were defined by classification of plant species composition in 226 50 × 50-m quadrats. There was no relationship between island size and species richness at the quadrat level, at least for the most extensive vegetation types. The vegetation of the islands is now composed of two main elements—an original set of communities (mostly of heath, tussock grassland and eucalypt open forest) whose species have poor inter-island dispersal, and a set of more recent colonists (mostly of strand, mangrove and coastal thicket communities). The former group is allied to the sandstone flora of western Arnhem Land, but is species-poor in comparison, as the islands lack the deep gorges which drive much of the species richness of western Arnhem Land. The latter group comprises many species with a broad geographic range across tropical coastal areas, including many species which have been shown elsewhere to be highly vagile. Many species of the former set appear to have been lost from the smaller islands. The island flora has been influenced by three sets of human managers. Aboriginal use of the islands has been long-standing and probably resulted in a fire regime which may have accentuated environmental patchiness. Centuries of wet-season use of some islands by Macassan trepang-harvesters, ending early this century, has apparently left few effects other than the persistence of occasional small populations of an introduced food tree. In contrast, European use of these islands has been minimal and fleeting, but is associated with the introduction of most weeds.

A different fauna?: captures of vertebrates in a pipeline trench, compared with conventional survey techniques; and a consideration of mortality patterns in a pipeline trench

We sampled the vertebrate fauna caught in a pipeline trench near Daly Waters, Northern Territory in the mid Dry season of 1999, and compared the species composition with that of a standardised quadrat-based survey protocol (using pitfall traps, Elliott traps and nocturnal and diurnal active searches). The proportion of records of snakes, pygopodids, frogs, two dragon species, the gecko Diplodactylus ciliaris and the rodent Pseudomys delicatulus was markedly greater in the pipeline than in the quadrat-based survey; this disparity was also evident in a pronounced size difference in the reptile species composition of the two techniques. The comparison demonstrates that the standard survey protocol has substantial biases against some species and groups of species and that additional sampling effort or specific new trapping techniques may be required for these taxa.The species composition of captures in this pipeline study differed substantially from the results from a larger section of this pipeline route con...