In drier districts, all sexually mature females in a herd may come into oestrus at the same time and it is thought that this is synchronised by male sexual activity. This can reduce the effects of predation by having a glut of potential victims in the form of young kids all of the same age.
Females can begin breeding at 6 months of age or when they weigh over 15 kg. Males reach sexual maturity at approximately 8 months, but competition for access to oestrus females is fierce and it is unlikely that young males are able to mate until they become large, dominant individuals. Females may become pregnant in their first year and can become pregnant again soon after giving birth, as lactation does not stop oestrus or pregnancy.
Therefore, they can breed twice in a year, as their usual gestation period is only days. Twins and triplets are common, although it is very rare for all three triplets to be raised to independence. The average litter size is 1. Females that are about to give birth leave the group and give birth in a protected spot. Kids are fully active soon after birth, but most, although not all, are hidden by their mothers and visited only for feeding.
A few days after birth they join the mother on her travels. Females may then remain separate from herds containing adult males for 1 to 2 months. The mortality rate of kids from birth to 6 months is high. 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. 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, to 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.
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 vary 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. In pastoral regions goat movements are generally much larger, with non-exclusive home ranges.
These are usually centred close to, or around, permanent water. Adult male goats are also highly reliant on scent to indicate dominance and physical condition. Adult male goats display dominance through a variety of contact and non-contact methods. Non-contact threats include staring, facing a rival with the chin down and horns forward, rushing or rearing. Encounters where physical contact occurs include pushing, head butting, engaging horns and rearing up and clashing. Feral goats are highly social animals and have reasonably complex systems of communication which includes smell, sight and sound.
When a female goat detects danger, she will stand rigid with ears towards the source of alarm. Kids respond by running to the relative safety of the female.
Female goats may also snort loudly and repeatedly to alert nearby goats to the danger. Depending on the threat, the group may flee, move away slowly, or return to their previous activities. Feral goats are opportunistic browsers that generally select the highest quality foods available.
They will eat:. Despite their tendency to select high-quality foods, feral goats can eat most plant species in Australia. This includes many plants that are toxic, spiny and bitter which sheep and cattle are likely to avoid. An average-sized goat requires between 2 and 4. Despite this, some goats in cooler and wetter climates are able to obtain the majority of their water from their food, meaning they are capable of surviving in areas with limited permanent fresh water.
Feral goats can establish populations in any area where food, water and protection from predators is available. In Victoria, feral goats tend to be able to establish and maintain populations in the semi-arid environments of the north west and the mountainous terrain of the Grampians, Alpine and East Gippsland regions.
In mountain regions, feral goats can live at high altitudes where there is food and water available. Goats are skilled rock and log climbers, and regularly use caves and rock overhangs for shelter. Wild dogs and dingoes are the most significant predators of feral goats in Australia. Feral pigs, crocodiles, foxes and large eagles may also prey upon feral goats, particularly goat kids.
Feral goats are susceptible to many exotic livestock diseases that are not present in Australia including:. Feral goats are also susceptible to several endemic diseases currently found in Australia including:.
Additionally, feral goats may also spread diseases to domestic livestock including sheep and goat herds. Feral goats can breed all year round, but breeding tends to peak during autumn with less in spring.
Feral goat breeding is influenced by environmental factors including drought, population dynamics, food and water availability. Despite variations in breeding seasons, all sexually mature female goats commonly come into oestrus at about the same time. As many populations of feral goats have a higher proportion of females than males, population growth can be high.
It is generally accepted that a population has the potential to double in size every 1. Female goats are sexually mature from six months of age and can produce young twice a year, with a gestation period of only days.
Twins and triplets are relatively common among domestic and feral goat populations, but most feral goats tend to have singles or twins. Dispersal of feral goats depends on availability of food, water and shelter. Feral goats prefer to maintain a small home range and traditional camp sites where possible, but will disperse when food and water becomes scarce.
Young female goats will stay with their family group throughout their lives, while males will leave these groups at puberty and join bachelor groups. From day-to-day large herds may will separate into smaller subgroups during the day and re-unite at night at common camp sites.
As a selective browser, feral goats can drastically impact on specific plant communities over a relatively short period. Goats are also capable of climbing trees where branches and trunks are on suitable angles, enabling them to graze much higher than kangaroos or sheep.
Their damage is most obvious and most severe on small islands. Many pastoralists in Australia now consider the capture and sale of feral goats to be an essential part of their business. Local eradication is usually only possible on small islands and in some mainland pockets.
In most areas, sustained management is required. Managers need to understand the relationship between the density of feral goats and the damage that they cause so that they can determine how to maximise the benefits compared to the costs of management.
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