The first European settlers to Australia brought with them dairy goats while subsequent introductions of various breeds used for meat and fibre have also occurred. Multiple escapes, abandonments and deliberate releases of all of these breeds have given rise to what we now know as the feral goat Capra hircus. While the feral goat is derived recently from mixed domestic origins, their earlier, wild ancestry is from the arid Middle-East making it well adapted for survival and persistence in the Australian semi-arid woodlands and rangelands including the South Australian Murray Mallee.
Feral goat populations have increased across much of the Australian rangelands over recent decades where they compete for feed in a pastoral setting with sheep. Their numbers and distribution are better understood in the pastoral zone where landholders are very conscious of their competitive impact and broad scale control methods are more effective. Of recent times they have also been seen as a valuable commodity with the price of goat meat increasing markedly on a growing export market. However feral goats are also found in the agricultural zone, and in the South Australian Murray Mallee they are known particularly from the sandy country adjoining the Victorian border and the Western Murray plains adjoining the rangelands to the north.
The arid adaptation of feral goat digestive biology means that they have the ability to extract their nutrient and energy requirements from a very wide range of vegetation types. Like most herbivores they will concentrate on the best feed available at any time and place but they are capable of digesting extremely fibrous and hard plant material or will even eat the thorny tissues on some plants while they are in the green and growing phase. The range of plants and tissue forms that is palatable to feral goats is far broader than that of sheep and even kangaroos meaning they are able to persist longer in any location and inflict far greater grazing impacts if not controlled.
Feral goats also extract much of their water requirements from the vegetation meaning in wetter periods they can range for 2-3 days away from standing water. In hotter, drier seasons and in drought however feral goats need to drink daily. These adaptations mean that feral goats can usually maintain an essentially sedentary habit and have fairly small home ranges. Conversely, tracking studies show that they are capable of long distance episodic movements presumably in response to dwindling local resources, then settling again into a sedentary existence once a suitable new location has been found.
When vegetation condition improves in response to cooler wetter seasons and large rainfall events such as La Niña, feral goat home ranges increase in size as they are able to range further from water and their population sizes can increase rapidly. Their great flexibility in diet and ability to respond quickly to changes in vegetation and the environment enables feral goats to have far greater impacts beyond competition with livestock and native herbivores for food.
As goats tend to strip the soft tissue from plant stems leaving bare terminals, they often remove not only the leaves but also the reproductive organs of plants preventing fruiting and the recruitment of new individuals. Since shrubby plant recruitment in the mallee tends to be episodic (in response to the same conditions that can give rise to increases in goat numbers) any new recruits that do germinate are then very susceptible due to their soft palatable growing tissues. After prolonged grazing pressure this results in changes in the floristic composition of native vegetation as plant species are lost from the community starting with the most palatable species. Shrubs that grow under these grazing conditions also take on unnatural physical forms. Shrubs must grow beyond a height of almost two metres to get foliage beyond reach since feral goats routinely stand on their hind legs to reach food if necessary. Feral goats in high densities and in harsh conditions can also chew stems back to the thickness of a finger. Subsequent regrowth from these tissues results in heavily modified plant form. These floristic and structural changes along with soil erosion from hard hooves and the subsequent lack of leaf litter and ground covering vegetation can destroy the habitat of native fauna including many species of ground frequenting and shrub dwelling bird species as well as reptiles and small mammals.
Goat browse impact monitoring in the Riverland Biosphere has shown that targeted removals of goats by trapping, shooting and mustering along with removal of access to standing water can have a lasting reduction in feral goat impact. Harvesting of animals alone is unlikely to be cost effective even with high meat prices if the goal is to reduce goat populations sufficiently to release pressure on vegetation and habitat. However in areas where unused dams have been flattened or access to stock water has been otherwise controlled, individually remeasured plants that show evidence of repeated historical browse events have put on significant growth in five years since initial measurements.
Since the increase of feral goat population size (as conditions improve) is likely to be proportional to the base (reserve) population that survives through drought, long term effective control is also dependent upon persistent and targeted removals when overall population densities are low. This is best achieved through monitoring for signs of goats and trapping around water sources. Feral goats can be detected by their distinctive hoof prints, droppings and signs of browse on native vegetation. In semi-arid woodlands and rangelands, stems chewed back to a thickness much greater than a match-stick are likely the result of goat browse.
Advice on feral goat control can be sought from Natural Resources SA Murray-Darling Basin local district NRM Officers or by phoning the Natural Resources Centre, Murray Bridge on 8532 9100.
Photo caption: Feral goats trashing a malleefowl mound south of Lameroo.
Photo credit: Fiona Gray, DEWNR
The feral goat browse monitoring in the Riverland Biosphere project was supported by the SA Murray-Darling Basin Natural Resources Management Board through funding from the Australian Government’s National Landcare Programme and the NRM Levies.