Suchergebnisse

The impact of feral goats (Capra hircus) on the rate of erosion in steep gorge country was estimated. The erosion (sediment flux) in a manipulated treatment area before and after the removal of goats was compared with erosion in two adjacent unmanipulated areas: one with goats at high density (~20 goats km–2) and one with very few goats (~0.2 goats km–2). Erosion was measured with 36 2-m-wide catch fences, collecting debris (soil and rock) moving down 40° slopes over 10 collection periods spanning 31 months. In the central manipulated area, goats were initially at high density but were completely removed during the third collection period.
Over the 10 collection periods, erosion was consistently greater in the area with many goats than in the area with few goats (mean five times greater, range 2.4–11.8). This difference was significant for 6 of the 10 collection periods. Before goats were removed from the manipulated treatment, the erosion in this area was not significantly different from that in the area with many goats, but was significantly greater than the area with few goats. After goat removal erosion in the manipulated area decreased relative to each of the other treatments. By the final collection period erosion in the manipulated (goats removed) area was significantly less than in the area with many goats, but not significantly different from the area with few goats.
Initial reduction in erosion following goat removal was rapid, followed by a continued slower decline over the next two years coincident with a relative increase in ground-cover vegetation. It was thought that both direct physical disturbance by the goats and secondary effects due to goat impacts on the substrate and ground-cover vegetation contributed to the increase in erosion associated with the presence of goats.

The impacts of feral goats in rainforests and thickets of the Macleay River system were studied. Rainforest floristics and diversity and goat browsing were measured over five years in a large-scale experiment with two experimental controls (density <1 goat km–2 and density ~20 goats km–2), and a goat-removal treatment (670-ha exclosure, initial density ~20 goats km–2). Feral goats browsed forb, shrub, tree and vine species. Sites with many goats were browsed at significantly higher levels than sites from which goats were removed and sites where goats occurred at very low density (<1 goat km–2). Contrary to findings in other studies, no plant species declined substantially where goat densities remained high throughout the study. Only the native forb Urtica incisa increased markedly following removal of goats. High goat numbers were not linked to increased exotic species abundances. At the community scale, species richness, diversity and evenness did not vary substantially among treatments in any year, nor did ordinations of sites (multidimensional scaling) reveal any pattern of site similarity between years that could be related to either goat presence or absence. Rainfall may have influenced plant density and masked the effects of feral goats. Rainforests in the region appear to be resilient to browsing under present feral goat densities, probably because goats feed predominantly in adjacent grassy woodlands and forests. However, we recommend a precautionary approach to feral goat management as these rainforests and thickets are of high conservation value.

The success of aerial shooting to control feral goats in arid and semi-arid
environments has lead to its widespread use in rugged and more densely
vegetated terrain elsewhere in Australia. In this experiment, the
method's effectiveness with and without the aid of ground spotters to
assist in locating goats was evaluated in such terrain in the Chandler River
Gorge near Armidale, New South Wales. The abundance of goats was estimated by
applying a correction factor (1.45) to indices of abundance made by ground
survey. Ground observers monitored success during the cull. Overall, only
31% of an estimated 462 goats were culled, at an average cost of
$61 per goat. In all, 50% of the goats were in herds never seen
by the helicopter crew, while the remaining 19% were individuals that
escaped (17% unseen from the air) from herds that were shot at.
Inconsistent culling success, combined with marked differences in the
behaviour of goats in different experimental blocks, suggested that variable
prior exposure to aerial shooting had a significant and confounding effect on
the experimental outcome. Where goats had no prior experience of aerial
shooting, culling success was 40% without spotter assistance and
59% with spotter assistance. Where there had been a history of aerial
shooting the ground observers reported a marked increase in evasive behaviour,
and the cull was only 21% even with spotter assistance. These results
show that aerial shooting is not as successful in this type of terrain as has
been assumed and suggest that its repeated or exclusive use will result in
declining effectiveness as goats learn to evade the helicopter.

Abstract Context Species Distribution Models (SDM) can be used to investigate and understand relationships between species occurrence and environmental variables, so as to predict potential distribution. These predictions can facilitate conservation actions and management decisions. Oxley Wild Rivers National Park (OWRNP) is regarded as an important stronghold for the threatened brush-tailed rock-wallaby (Petrogale penicillata), on the basis of the presence of the largest known metapopulation of the species. Adequate knowledge of the species' ecology and distribution in OWRNP is a key objective in the national recovery plan for the species occurring in the Park. Aims To model distribution using key GIS-derived environmental factors for the brush-tailed rock-wallaby in OWRNP and to ground-truth its presence through field surveys in areas of high habitat suitability. Methods We used Maxent to model the distribution of the brush-tailed rock-wallaby within OWRNP on the basis of 282 occurrence records collected from an online database, elicitation of informal records from experts, helicopter surveys and historic records. Environmental variables used in the analysis were aspect, distance to water, elevation, geology type, slope and vegetation type. Key results Vegetation type (37.9%) was the highest contributing predictor of suitable habitat, whereas aspect (4.8%) contributed the least. The model produced an area under the curve (AUC) of the receiver operating characteristic (ROC) of 0.780. The model was able to discriminate between suitable and non-suitable habitat for brush-tailed rock-wallabies. Areas identified in our model as being highly suitable yielded eight new occurrence records during subsequent ground-truthing field surveys. Conclusions Brush-tailed rock-wallaby distribution in OWRNP is primarily associated with vegetation type, followed by distance to water, elevation, geology, slope and aspect. Field surveys indicated that the model was able to identify areas of high habitat suitability. Implications This model represents the first predicted distribution of brush-tailed rock-wallaby in OWRNP. By identifying areas of high habitat suitability, it can be used to survey and monitor the species in OWRNP, and, thus, contribute to its management and conservation within the Park.

Between 2000 and 2002 two populations of the spotted-tailed quoll (Dasyurus maculatus) were studied on the New England Tablelands using trapping surveys and radio-tracking. Overall, 85 individuals were trapped, but only two individuals were trapped throughout the 26 months of the study. Trapping was male-biased (74%). Adult males (>1 year) were substantially larger than females. On average, males travelled longer distances than females, and the maximum distances recorded were 8.1 and 3.9 km for a male and female respectively. Home ranges of males overlapped substantially, whereas those of females appeared to be exclusive. Mortality rates and the turnover in the quoll populations appeared to be substantial and at the beginning of autumn the populations comprised ~50% juveniles.