Aspects of the ecology of the cat, fox and dog in the south-east forests of NSW : their potential impact on native species in forests managed for the production of timber

Abstract

The principle objective of this study was to examine the potential impact of the Cat, Fox and dog on native species, in particular those that are prey of these predators, in native forests that are principally managed for the production of timber in south-east NSW. This was examined initially by investigating the relative effectiveness of four techniques for surveying the Cat, Fox and dog, viz:- (i) spotlighting, (ii) scat surveys, (iii) scent-station surveys; and (iv) hair-tube surveys. The results from the surveys provided information on: (i) the distribution of the Cat, Fox and dog in relation to roads, forest edges and remote forest environments; and (ii) the relative abundance of the Fox and dog in the region. The results from the surveys were also used to investigate habitat attributes that potentially influence the abundance of the Fox and dog in the region. The extent that the Cat, Fox and dog used habitat in the vicinity of roads and habitat away from roads also was investigated using hair-tubes and radiotracking techniques. Scat surveys provided information on the diet of the Fox and dog. Results from diet analyses and spotlight surveys were used to explore whether the Fox and dog were opportunistic or selective in their choice of prey. The relative risk of prey species to predation by the Fox and dog also was assessed. Finally, the data collected in this study provided an opportunity to explore the efficacy of poison-baiting for reducing the abundance of the Fox and dog in the region during the period of the study. v The study region was stratified using environmental domains (Richards et al. 1990) to place it in a broader environmental context and to identify the environmental variation within it. To provide a comparative basis for field research, the environmental domains were grouped into two areas, viz:- the coastal and escarpment area. Within each of the two areas 15 sites were identified for survey purposes. Spotlighting, scat collection, scent-stations and hair-tubes were found not to be equally effective for surveying the Cat, Fox and dog in the region. Spotlighting was found to be the least effective method for detecting these species. Scat surveys provided information on the distribution and relative abundance of the Fox and dog, but was ineffective for detecting the Cat. Hair-tubes detected the Cat and dog, but not the Fox, despite observations of the Fox close to hair-tubes. With the exception of data collected from scat surveys, statistical analyses were limited due to small sample sizes. As a consequence, some of the analyses are descriptive and should be considered as an exploratory investigation only. The dog was found to be equally abundant both in the coastal and the escarpment areas, and significantly more abundant and widespread than the Fox. The Fox was significantly more abundant in the coastal area. The abundance of the Fox and dog varied significantly between survey periods and there was significant variation in their abundance within each area. Following poison-baiting, the abundance of the Fox and dog decreased at sites where poison-baiting occurred. However, this was not statistically significant. Hair-tube surveys detected the Cat and dog on roads, in edge habitat (areas within 500 m of a road) and in areas more than 1.5 km from roads (or remote areas). The Fox was also detected in all three habitat types from scats and by observation. In addition, radio-tracking found that one Cat preferred habitat more than 500 m from roads. The remains of 29 mammal species were found in the scats of the Fox and dog during the study. Large mammal species (i.e., those with an adult body weight greater than 10 kg), and in particular the Swamp Wallaby, were the most common prey of the dog. Large mammals formed more than 50% of its diet. Correspondingly, these species were also found to be most at risk from predation by the dog. Medium-sized marrunal species (i.e., those with an adult body weight between 0.75-10 kg) formed approximately one-third of the diet of the dog. The remainder of the diet consisted of small mammal species (i.e., those with an adult body weight less than 0.75 kg). Small mammals were the most common prey of the Fox. The Dusky Antechinus, Brown Antechinus, Bush Rat and Black Rat each formed more than 5% of the diet of the Fox. These species were also found to be more at risk from predation by the Fox than large and medium-sized mammals. Approximately one-third of the diet of the Fox consisted of medium-sized mammals, in particular the Rabbit, closely followed by the Common Ringtail Possum. The extent to which the Fox and the dog were opportunistic or selective predators was not clear from this study. Overall, the most common large and medium-sized species in the diet<> of the dog and Fox also were relatively more abundant (e.g., the Swamp Wallaby, brushtail possums and Common Ringtail Possum). This suggested that the dog and Fox hunted these species in proportion to their abundance (i.e., opportunistically). However, this relationship was not always consistent. The abundance of the dog, rainfall, and time since logging were found to be significantly correlated with the abundance of the Fox in the region. A number of factors, such as resource partitioning of prey by the dog and Fox, potentially greater abundances of small mammals in drier forests, and relative ease of foraging by the Fox in recently logged and perhaps unlogged forests, may have partially explained these results. No habitat attributes were found to explain significantly the abundance of the dog in the region. The results from this study clearly indicate that the Cat, Fox and dog are widespread in the region and the Fox and dog are relatively abundant. The evidence from this study and other studies suggest that in forest environments most mammal species, with the exception of bats and some arboreal species, are potential prey for these predators. This may have consequences for the survival of native species, particularly Critical Weight Range (CWR) species (i.e., those with an adult body weight between 35-5500 g) and ground-dwelling mammals that are rare and/ or endangered, in these forests. As small mammals were found to be most at risk from predation by the Fox, it may be a greater threat to CWR species and species that are rare and/ or endangered. It is possible that high levels of predation by feral predators can suppress small populations to the extent that they cannot recover (i.e., predator-pit) and thus are more prone to extinction from stochastic events. In the absence of knowledge, such as the range of prey densities over which feral predators exert a regulatory role, endangered and naturally rare prey species may be able to persist in the presence of the Cat, Fox and dog provided that: (i) relatively dense understorey vegetation (i.e., their habitat) is maintained to provide refugia; and (ii) feral predator populations are effectively controlled to minimise their potential impact.