Feral goats threaten the biodiversity of native plants and animals and compete with domestic livestock for food water and shelter.
Description
The goat was one of the first animals to arrive in Australia with the First Fleet in 1788. Present feral goat populations are descendants of animals introduced for a variety of reason since that time.
Goats were spread around Australia by settlers, railway construction gangs and miners who used these domesticated animals as a source of milk and meat. These domestic goats escaped, were abandoned or were deliberately released and established feral herds.
Distribution
Feral goats are found in many areas of NSW, including arid and semi-arid rangelands, as well as higher rainfall and agricultural areas of eastern NSW. They have benefited from sheep grazing practices and the provision of artificial water points throughout the dryer regions of NSW.
Feral goats are most common on rocky or hilly country in the semi-arid rangelands. These areas provide security from predators and disturbance by humans. They are not normally found on flat treeless plains. However, they can be found on flat country with dense shrub cover.
Favourable habitat requires availability of shelter, surface water and an abundance of preferred food species. Large numbers of goats do not occur in areas where dingoes are abundant.
Diet
Goats are generalist herbivores that select the highest quality food available.
They will eat:
- foliage, twigs, bark, flowers, fruit and roots
- plant litter, seeds and fungi
- many poisonous or bitter plants and species avoided by sheep and cattle.
Though goats will eat just about anything, they are highly selective feeders and specific shrubs, grasses or herbs may comprise the principal part of the goats diet at different times or at different locations.
During dry times goats need to drink water. An average-sized goat will drink between 2 and 4.5 L of water per day, depending upon temperatures, humidity and reproductive status. Some goats, particularly those in temperate or wet climates, can obtain most of their water requirements from their food and can survive in areas with no permanent fresh water.
Reproduction
Feral goats can breed at any time of the year.
Female goats (does):
- can begin breeding at 6 months of age or when they weight 15 kg
- have a gestation period of 150 days
- can breed again soon after giving birth, therefore can give birth twice a year
- often have twins or triplets, although successfully raising all three triplets is rare
- leave the herd and give birth in a protected location, and the kids are active soon after birth. They are often hidden by their mothers and only visited for feeding for the first few days before following their mothers on her travels.
Goats have the potential to double their population every 1.6 years in the absence of mortality caused by human control efforts and predation.
Social structure
Feral goats are social animals and are found in herds, the basic social unit being adult females and their recent offspring. The males leave these matriarchal groups to form loose associations with similar aged males or larger mixed-aged groups, which associate with the female's home range during the breeding season but range over larger areas at other times.
Group size within herds of feral goats varies on both a daily and seasonal basis. Much of the seasonal variation seems to be related to the availability of surface water. When water is abundant, groups are generally small and well dispersed. During drier months, groups come together and increase in size, consisting of both males and females of all age classes.
During droughts they tend to congregate in large numbers, 500 to 800 goats and remain near water.
Group composition is highly variable. Feral goats are continually forming, breaking and re-amalgamating herds. Many new associations are formed when congregating around water sources.
Life span and mortality
The mortality rate of kids from birth to 6 months is high. Natural mortality rates amongst older goats are unknown but assumed to be about 10%. Adult mortality rates, from all causes including hunting and harvesting are about 26% in temperate regions.
Wild dogs, foxes, wedge-tailed eagles and feral pigs are all predators of feral goats. Wild dogs are the main predators of adult goats and appear to affect feral goat distribution. In northern Australia, goats are rarely present unless wild dogs are absent or controlled to low densities. Foxes are the main predators of feral goat kids in eastern Australia.
Goat populations can rapidly replenish after vigorous control programs. High levels of removal of feral goats from a population may increase survival rates and result in a faster than normal rate of increase. Goats have the potential to double their population every 1.6 years in the absence of mortality caused by human control efforts and predation.
Movements and home ranges
A good knowledge of the home range of feral goats is a prerequisite to both the effective management of this animal as a resource and the establishment of appropriate strategies for control.
The size of the home ranges of feral goats varies across Australia, being smaller in areas where food, water and shelter are freely available and much larger in semi-arid pastoral regions. The boundaries of these areas are not rigidly defined and are not actively defended to exclude other goats.
Feral goats in higher rainfall areas with ample water and food have small, non-exclusive home ranges generally of about 1.0 to 13.5 km2, with males having larger ranges than females. In pastoral regions goat movements are generally much larger, with non-exclusive home ranges. These are usually centred close to, or around, permanent water. Radio tracking of goats on Yerilla Station, in the pastoral area of Western Australia showed the average female home range was 50 km2 ranging from 14 to 118 km2. Males averaged 271 km2, ranging from 102 to 460 km2. Data recorded from the Broken Hill region also confirm similar large home ranges.
Long distance movements of goats have been recorded in semi-arid regions. One male in western NSW moved 87 km in a 10-month period. This degree of mobility makes goat control very difficult, as the rate of reinfestation can be very high. It also makes eradication or containment almost impossible in the event of an exotic disease outbreak. However, feral goats in higher rainfall zones are more sedentary, with few goats moving permanently outside their home range.
Impacts
Competition and habitat degradation by feral goats are listed as a Key Threatening Process (KTP) under the Threatened Special Conservation Act 1995.
Feral goats:
- compete with both native animals and domestic livestock for food, water and shelter especially during drought conditions
- have very destructive grazing habits, as they can completely strip shrubs of bark and leaves
- can destroy the vegetation cover and disturb the balance of species in a vegetation community
- spread weeds
- cause soil erosion by overgrazing areas and disturbing the soil with their movements sharp hoofs and pawing of the ground
- damage, heritage sites, infrastructure and fencing.
Feral goats can carry internal and external parasites, some of which affect sheep and cattle. They can:
- can carry and spread ovine footrot
- act as a reservoir for, and be a vector of, exotic diseases, including foot and mouth, rabies, bluetongue and rindepest.