Brumbies are wild horses that evolved from ordinary domesticated horses. These animals escaped from their domesticated human environments and reverted to being wild animals. They look pretty much like common everyday horses. The only difference is that they are wild. These wild horses are referred to as Feral horses.
Horses arrived in Australia with the first European settlers on the First Fleet in 1788. Many additional horses were imported from that time onwards.
Predominately used in farming, transportation and horse racing, these animals were usually grazed in unfenced properties, and many subsequently escaped. The first recorded case of a wild horse was in 1804. We are not certain if this animal escaped or was abandoned by its owner. As horses were replaced by mechanisation, many horses were intentionally released into the 'wild' and had to fend for themselves.
Feral horses look pretty much like the common everyday domesticated horses. Having descended from animals that had survived the treacherous journey by sea from England, Europe, and Asia, where only the strongest horses survived, Brumbies are particularly hardy and have adapted well to the harsh Australian Outback. Being free-roaming, feral horses are usually leaner and more muscular than domesticated horses. It is estimated that there are about 400,000 feral horses in Australia today.
The horse is a herbivorous, ungulate placental mammal. That is; it eats only vegetation, has hooves, carries its young inside its body and feeds its babies milk. A horse can live f0r 20-30 years.
Horses are herbivores whose food of choice is grass. They also eat fobes (flowering, herbaceous broad-leaf plants) and browse on tree branches and shrubs. Horses have a single small stomach, unlike cows which have four that are much larger. For this reason, to get enough food, a horse must feed for 15 to 17 hours each day. Horses often eat soil and visit mineral and salt licks to supplement their diets with essential nutrients, including salt, potassium, sodium, calcium, and magnesium, which are present in the soil but lacking in their diets.
Feral horses have adapted well to the Australian environment. They are found in various habitats such as tropical grasslands, wetlands, semiarid plains, rocky ranges, temperate ranges, sub-alpine forests, and some small offshore islands. They prefer grassland and shrub-land with plentiful water and pasture. They can travel up to 50 km a day in search of food and water.
The biggest threats to brumbies are droughts when they may starve to death of hunger and thirst, and by regularly culling by humans to keep their numbers in check.
The impact of feral horses on native Australian flora and fauna is indeed real. However, the true magnitude of the problem hasn't been clearly determined, and much exaggeration and misinformation prevails. The environmental impacts attributed to the feral horse are just as applicable and relevant to other ungulates (hoofed animals) such as sheep and cattle raised on a massive scale by pastoralists and farmers. From an Australian environmental perspective every one of these ungulated animals also have significant impact the Australian environment. Because the horse is no longer an economically beneficial animal it is overly vilified.
Ungulates such as horses are hoofed animals, while all Australian native animals are essentially soft-footed. Australian native vegetation, having evolved without being trampled by hard hooves, suffer significant damage from hoofed animals.
The detrimental impacts of the feral horse are as follows.
Horses trample and overgraze near streams and water catchments increasing run-off and reducing water quality. This can lead to downstream siltation and water ponding. Trampling in waterways also kill underwater vegetation, and increase stream depth and stream pugging (compacting the soil).
The hard hooves of feral horses increase soil compaction, soil erosion and soil loss. This, in turn, reduces water infiltration and soil productivity.
By consuming and trampling native vegetation, feral horses may impact local plant species diversity thereby altering the local vegetation.
In Australia, 156 species of non-native plants can germinate in horse dung, including 16 noxious weeds. Furthermore trampling and killing native vegetation facilitates weed invasion.
By altering and impacting on the local fauna, feral horses indirectly impact the viability of native Australia animals which rely on specific plant species for survival.