Age, Movements and the Management of the Wedge-Tailed Eagle, Aquila-Audax, in Arid Western Australia

The breeding of the Wedge‐tailed Eagle Aquila audax was investigated in four areas of the arid zone of Western Australia from 1968 to 1976, with some supporting data from the adjacent Mediterranean zone. Breeding was dependent on, and geared to, the occurrence of a minimum level of available prey. In the arid zone the seasonally most regular occurrence of the low rainfall, combined with greatest diversity of vegetation and prey, was associated with the most regular breeding and the greatest annual productivity of young per pair. At the other extreme, where an identical mean annual rainfall was distributed more erratically between seasons and years and was combined with a less diverse flora, the prey available to eagles was restricted to virtually one species–the introduced European rabbit Oryctolagus cuniculus. In this situation there were gaps of up to 4 years between the breeding of eagles, because of major fluctuations in the size of the population of its rabbit prey. Their density was actually greatest in those areas where the widely fluctuating food supply occasionally allowed them to breed with considerable success; however, this did not compensate fully for the irregularity of breeding. Where the prey available was thus restricted to a single species and was least stable, the area may have been unable to support a population which could maintain itself without recruitment from outside.Breeding success in the Mediterranean zone was higher than in the arid zone. The Wedge‐tailed Eagle's breeding strategy is conservative (with ’k‐selected‘ characteristics), but this study shows that it is ecologically successful in both zones, although least so where the climate is extremely erratic.

SummaryRidpath, M.G. & Brooker, M.G. (1987), Sites and spacing of nests as determinants of Wedge-tailed Eagle breeding in arid Western Australia. Emu 87, 143–149.Wedge-tailed Eagles Aquila audax in the arid zone of Western Australia built their nests mainly in the top half of typical members of the commonest species of trees higher than 4 m. Most nests in the arid zone were 2–6 m from the ground, with a few at less than 1 m, and in the mediterranean zone at 4–16 m. Breeding success in the arid and mediterranean zones did not vary with the height of the nest and was similar in live and dead trees. Most territories contained several nest-sites, used and re-used in different years. The availability of nest-sites did not limit breeding density in the arid zone. Mean size of territories in the arid zone ranged from 30 to 100 km2 and was probably related to long-term availability of prey. The smallest territories occurred in the areas of most erratic rainfall, where prey were very scarce for long periods and very abundant for brief periods. We conclude that territoriality sets an upper limit to the density of potential breeding pairs in any particular habitat.

Australia's arid zone is characterized by unpredictable extremes in climate, and abundance and quality of biotic resources. Ecological theory and definitions derived from relatively stable environments in the northern hemisphere do not fit well in Australian deserts. We illustrate this by describing a range of moving behaviours of 46 radio-collared red kangaroos in the Gascoyne region of Western Australia, which we believe are facultatively employed to maximize survival in arid environments. Tracking occurred every 2 months on average during the last 6 months of a 23-month long drought and for the following 27 months. Home range size was highly variable and averaged 18.4 ± 5.0 km 2 for adult females [MAP(95) ± 1 SEM] and 36.1 ± 17.2 km 2 for adult males

The Litoria rubella species complex (L. capitula and L. rubella) is distributed across much of continental Australia, southern New Guinea, and the Tanimbar Islands of Indonesia, in habitats ranging from deserts to tropical forests. We carried out an appraisal of molecular genetics, advertisement calls, and morphological variation in the species complex. Analyses of thousands of nuclear gene SNPs and nucleotide sequences from the mitochondrial ND4 gene identified four reciprocally monophyletic lineages in both marker types, two exclusively in Australia, one in Australia/New Guinea and one from the Tanimbar Islands. The advertisement calls of the three lineages on continental Australia have overlapping but significant differences in the number of pulses in the notes, dominant frequency, and call duration, particularly where the lineages come into contact. The Tanimbar Islands lineage is genetically and morphologically distinct and represents L. capitula. Molecular and advertisement call data together support the recognition of three species in Australia: a widespread central arid and northern tropics lineage, a western arid zone lineage, and an eastern mesic lineage. Litoria rubella sensu stricto is widespread across the tropical Kimberley and Top End regions, southern New Guinea, the central arid zone, and the Murray Darling Basin, making it an extreme climate-generalist. SNP data indicates that L. rubella has gene flow to the north of the Lake Eyre Basin but not the south, making it a possible ring species. The western arid zone lineage does not differ in appearance or advertisement call from L. rubella but is geographically disjunct and phylogenetically distinct. The eastern lineage is primarily distributed to the east of the Great Dividing Range and Cape York in Queensland. We redescribe L. rubella sensu stricto, describe the eastern lineage and western arid lineage as new species, L. pyrina sp. nov. and L. larisonans sp. nov. respectively. Although L. rubella and L. larisonans sp. nov. are morphologically similar, they do not overlap in distribution, making identification non-problematic. Litoria pyrina sp. nov. can be distinguished from L. rubella at contact zones by having advertisement calls with a higher dominant frequency. We investigated the history and morphology of the type for L. mystacina and designate it a nomen dubium. The three Australian species are likely to have a conservation status of Least Concern as they are widespread and abundant, with no significant threats. Little is known about L. capitula from the Tanimbar Islands outside of the few existing museum specimens.

SummaryAlthough studies of seed banks in arid ecosystems are commonplace, they are lacking for the large arid zone of Western Australia. Across the six major plant communities fringing a large salt lake within this zone, topsoil (0–5 cm depth) was collected from 12 to 36 sites per community. Samples were dried, spread out on a bed of vermiculite in seedling trays and placed in a well‐watered glasshouse to determine the readily germinable component of the soil seed bank. Subsamples of topsoil were treated with smoke water, hot water or flooding to help determine seed bank of species with dormancy mechanisms. As with other studies of arid seed banks, large numbers of grasses and forbs emerged from the topsoil, with relatively small numbers of woody perennial species and hummock grasses (Triodia spp.) present, even in communities where such species were dominant. There were, however, a few exceptions where a reasonable density of dominant trees/shrub seed was present in topsoil. Soil treatment generally had limited effect on composition and density of emergent seedlings. Although floristic similarity between soil seed banks and corresponding above‐ground vegetation was modest, there were clear differences in soil seed bank composition between communities. The implications of the results for using topsoils to restore landforms of the study area after mining or other disturbance are discussed.

Long‐term studies are required to reveal responses by long‐lived, top‐order predator populations to ongoing seasonal fluctuations. However, such investigations are rare in the Australian context. Between 2009 and 2019, the breeding density and productivity of an arid and a mesic wedge‐tailed eagleAquila audaxpopulation, each occupying an area of 2800 km2, were compared (11–98 pairs monitored annually). Breeding pairs spaced themselves evenly in both study areas, with no significant difference between the average arid zone nearest‐neighbour distance of 5.32 ± 1.98 km (n = 44) and that determined for the mesic zone (4.88 ± 2.32 km,n = 54). This similarity in spacing suggests a maximum average density is tolerated by these territorial raptors. By contrast, annual breeding success (proportion of pairs fledging young) and productivity (fledged young per pair) differed significantly between the two populations, with rainfall (but not temperature) influencing reproduction. In the arid zone, the proportion of successful pairs per occupied breeding home range was consistently low each year (mean = 12 ± 7% fledged broods per pair, range 0–26%) and positively correlated with annual rainfall. In the mesic zone, it was consistently high each year (mean = 69 ± 9%, range 57–91%) and not significantly correlated with annual rainfall. Overall productivity figures showed similar differences, with 0.13 and 0.77 fledglings per pair per year for arid (n = 9 years) and mesic (n = 11 years) eagles, respectively. Such low arid zone productivity, the lowest ever recorded for the species, could have long‐term implications in the face of the increased frequency of extreme weather events. That breeding density can be independent of climatic factors provides new insight into the way a largeAquilaspecies integrates with Australia’s predominantly arid environment. This study provides an important baseline data set for continued research on long‐term occupancy and productivity trends.

Long-range movements of small mammals in arid Australia: implications for land management

Regional decadal precipitation reconstructions for the arid and semi-arid zones of northwestern China were established by the use of different palaeoclimate archives such as ice-cores, tree-rings, lake sediments and written historical documents. Local rainfall reconstructions from single sites were averaged to obtain regional precipitation records for a western and eastern region of an arid and semiarid zone of northern China, respectively. All established regional precipitation curves display 5 dry periods, each lasting about 50 years. Meanwhile, precipitation reconstructions show regional dissimilarities. During the last 500 years, the trends of precipitation change in the eastern arid region are basically consistent with those in the western and eastern regions of the semiarid zone. Precipitation variations in the western arid region are unique, showing significant local patterns of rainfall variability. Maximum entropy method (MEM) spectral estimates show that each regional precipitation series contains stationary century-scale periodicities of about 120a. Singular spectrum analysis was applied to isolate the century-scale oscillation signals from the regional proxy precipitation series. Significant periods with wavelengths of 121.4a, 154.6a, 124.3a, 118.6a, 108.5a and 121.4a were found that explain 26.56%, 26.44%, 28.87%, 18.67%, 33.48% and 34.04% of the variances of the original series for the western arid zone, the eastern arid zone, the whole arid zone, the western semiarid zone, the eastern semiarid zone and for whole northern China, respectively.

Decadal-scale precipitation variations in arid and semiarid zones of northern China during the last 500 years

Post-Eocene climate change across continental Australia and the diversification of Australasian spiny trapdoor spiders (Idiopidae: Arbanitinae)

Can pastoral grazing management satisfy endorsed conservation objectives in arid Western Australia?

The Gascoyne River catchment in arid Western Australia was presented as a desertification case study at the United Nations Conference on Desertification in Nairobi in 1977. The Gascoyne is similar to many other areas in Western Australia that were seriously degraded following the introduction of domestic livestock in the late 19th century. However, there have been many improvements in land manage- ment since the 1970s, with good evidence that much of the rangelands are now in better condition. These improvements have been the result of a combination of fac- tors, including: a comprehensive resource inventory; range assessment and ongoing monitoring information; a mixture of regulation and empowerment; capacity-building using a variety of approaches; and regional scale strategies aimed at taking a co-ordinated approach to land management issues. A strong emphasis on science was used to address technical issues and to improve the understanding of ecosystem dynamics. Of course, individual land managers play the primary role in land management. It is their day-to-day decisions that determine whether the land will continue to degrade or improve. In Western Australia, land managers are better educated than in the past, have a better sense of community expectations for land management and generally practice a more benign style of land management than their forebears.

Mangrove trees tend to be larger and mangrove communities more diverse in tropical latitudes, particularly where there is high rainfall. Variation in the structure, growth and productivity of mangrove forests over climatic gradients suggests they are sensitive to variations in climate, but evidence of changes in the structure and growth of mangrove trees in response to climatic variation is scarce. Bomb-pulse radiocarbon dating provides accurate dates of recent wood formation and tree age of tropical and subtropical tree species. Here, we used radiocarbon techniques combined with X-ray densitometry to develop a wood density chronology for the mangrove Avicennia marina in the Exmouth Gulf, Western Australia (WA). We tested whether wood density chronologies of A. marina were sensitive to variation in the Pacific Decadal Oscillation Index, which reflects temperature fluctuations in the Pacific Ocean and is linked to the instrumental rainfall record in north WA. We also determined growth rates in mangrove trees from the Exmouth Gulf, WA. We found that seaward fringing A. marina trees (∼10 cm diameter) were 48±1 to 89±23 years old (mean ± 1σ) and that their growth rates ranged from 4.08±2.36 to 5.30±3.33 mm/yr (mean ±1σ). The wood density of our studied mangrove trees decreased with increases in the Pacific Decadal Oscillation Index. Future predicted drying of the region will likely lead to further reductions in wood density and their associated growth rates in mangrove forests in the region.

Seasonal changes in standard metabolic rates in the white-browed scrubwren Sericornis frontalis (Acanthizidae) from arid, semi-arid and mesic environments

Context Some ecologists argue that nesting success and abundance of wedge-tailed eagles (Aquila audax) are strongly linked to the abundance of introduced wild rabbits (Oryctolagus cuniculus). Consequently, concerns were expressed about eagle population viability when the biological control agent rabbit haemorrhagic disease virus (RHDV) heavily reduced rabbit numbers. However, observations following the spread of rabbit haemorrhagic disease (RHD) in Australia and Spain (where Aquila adalberti is an equivalent of A. audax) question this assertion. Eagle numbers did not fall even though rabbits declined regionally by up to 90% in both countries. Aims To reconsider the assumption of a strong link between rabbit abundance and wedge-tailed eagle breeding and population maintenance. Dispelling misconceptions, if any, about the eagles’ dependence on rabbits would benefit the future management of both eagles and rabbits. Methods We reviewed the literature associated with claims that eagles were heavily dependent on rabbits and asked whether these views could be substantiated given the lack of changes in eagle abundance following the spread of RHD. Data on eagle egg-clutch size and nesting success were also reviewed. Conclusions There is little evidence that eagles depend heavily on rabbits as prey. Instead, as rabbits decline, more kangaroos, reptiles and birds are eaten, partly because more native prey becomes available. Eagles have a high proportion of rabbits in their diets mainly where degradation of natural ecosystems, including that caused by rabbits, results in native prey being rare or unavailable. There has been minimal variation in average clutch size following major perturbations in rabbit population size. Implications Rather than perpetuating the idea that high populations of rabbits are needed for wedge-tailed eagle conservation, resources would be better re-directed into understanding continental-scale eagle population dynamics. This would provide a more rational framework to assist decisions on future biological control agents for rabbits.