Explainer: Feral horses in Australia

There are an estimated 400,000 feral horses roaming Australia, an incredible number when you consider that they were introduced to the continent just over 200 years ago by European colonisers.

Despite the detrimental impacts of feral horses on our native wildlife and landscape, their management remains a controversial issue, and debate about how to best manage their population continues.

Let’s explore the science behind the issue.

A bit of background

Horses arrived in Australia with the First Fleet in 1788; in subsequent years the originals were followed by shipments of working farm horses. The first record of them escaping into the bush or being abandoned was in 1804, and their populations have boomed in the intervening centuries.

Most feral horses today occur in the vast cattle production areas of the Northern Territory, Queensland and some parts of Western Australia and South Australia. There are also scattered populations in Victoria and New South Wales. The most famous – or infamous, depending on your point of view – featured extensively in the news of late is the brumby population in Kosciuszko National Park.

Feral horses have no known predators, and their only significant natural threats are drought and severe bushfires. Left to their own devices, it’s estimated the population will continue to increase at a rate of 20% per year.

This is bad news, as introduced horses have a plethora of negative impacts on the landscape, native plants and animals, further adding to the ecosystem loss already being induced by other issues such as climate change.

Feral horse ecological impacts

Australia isn’t home to any native hard-hoofed mammals, and feral horses can cause immense ecological damage as a result – particularly in the fragile high country of the Australian Alps, including Alpine and Kosciuszko national parks. This was explored in detail in the 2019 SCINEMA International Science Film Festival documentary, Underfrog.

As large herbivores, horses need to consume substantial amounts of vegetation. Their constant feeding has impacts on native species as they compete for resources, and this also causes soil erosion through the removal of vegetation. In central Australia, feral horses overgraze large areas because they can travel up to 55 kilometres from water in search of food, and this can force native wildlife from their habitats.

Their trampling causes further landscape erosion and vegetation damage, as well as damage to waterways such as creeks, rivers and waterholes. These impacts can become more pronounced during drought, as they quickly degrade areas close to remote waterholes and natural springs that would normally become refuges for native wildlife.

Horse trails over streams also cause them to widen, become shallower and reduce their flow speed. This has been particularly damaging to the endangered stocky galaxias fish – which is only found in the headwaters of Tantangara Creek in Kosciuszko – as it can result in fine sediment settling between cobbles and boulders on the stream floor, which is where the galaxias shelter and spawn.

Feral horses are also a vector for the introduction and spread of weeds that compete with native species, through seeds carried in their dung, manes and tails that can be carried over the large distances they travel.

It’s a long list and the effects are cumulative.

Efforts to curb populations

The Australian government has put measures in place to control the populations of other feral species – for instance, predators such as cats, foxes, and rabbits – so what makes the issue of feral horses so difficult to deal with?

Last week the ABC’s Four Corners aired a documentary, Feral, which explored the clash of cultures over these controversial animals. For some, they are an important tie to Australia’s colonial history – think the iconic poem “The Man from Snowy River” by Australian bush poet Banjo Paterson. Others believe we should prioritise the future of native species and environments that have existed for thousands of years before horses came to Australia.

The cultural weight these animals hold, as well as animal welfare concerns, has made it difficult for policymakers to implement measures to deal with their numbers. This, in conjunction with the feasibility of different control measures across the country, means that management strategies vary from state to state.

These strategies can include trapping or mustering for commercial sale, translocation and rehoming, aerial and on-ground culling (shooting), and fertility control – depending on the scale, location and impact of the horses.

On-ground culling is humane and cheap, though limited to accessible areas, while aerial culling can reach areas inaccessible by land – but it must be carried out by properly trained and accredited shooters using approved procedures.

Fertility control has been seen as an attractive alternative to lethal measures to control populations, although it’s not an effective strategy as a sole management approach. Immunocontraceptive vaccines induce multi-year infertility (up to three years) in individual horses, though some formulations require booster treatments annually. Ultimately, the proportion of female horses that would need to be treated is likely to be greater than 50% of the population each year.

Since most wild-horse populations are dispersed over a large, varied and difficult-to-access terrain, accessing them for treatment is very difficult. Even so, it’s estimated that if vaccines were implemented, and used alone without lethal measures, it would take 10 to 20 years before populations began to decline.

The challenge of feral horses in Australia will not be solved with one silver-bullet treatment, but pulled from this diverse toolbox of approaches. According to the Australian Pest Animal Strategy 2017 to 2027, the management of pest animals is an ongoing task that will require a proactive and coordinated approach. Let’s hope we’re up for it.