Tracking the wild horse population

The wild horse survey uses the international best practice method for reliably estimating the population of large mammals over wide geographic areas, known as distance sampling. More than 2,000 peer-reviewed scientific papers use distance sampling to estimate wild animal populations.

The survey used standard distance sampling which was used in previous years. It also used mark-recapture distance sampling – a method first trialled in the 2024 survey – to strengthen the robustness of survey results.

The main difference between mark recapture distance sampling and standard distance sampling is that standard distance sampling assumes the observers see 100% of animals on the centreline of the transect (that is, at zero distance from the observer in the helicopter). Mark recapture distance sampling does not make the same assumption and includes an analysis to determine the proportion of horses that are seen on the centreline of the transect. As a result of this additional analysis, mark recapture distance sampling is regarded as providing a more accurate population estimate.

The survey is conducted from a helicopter across 3 large areas (survey blocks) covering around 37% or 2,535 square kilometres of the park. The areas have been known to support wild horse populations.

The 2025 survey used the same survey blocks as previous surveys, with one area around Cabramurra excluded in 2025 due to insufficient detections of wild horses in 2023 and 2024.

The helicopter flies a series of parallel lines, known as transects, in each survey block at a height of 61 metres and a speed of 93 km/hour. The 2025 survey design included additional transects in the northern and southern survey blocks to increase the precision of population estimates. The total length of transects flown in 2025 was 2,225.4 km.

Key details recorded by the observers in the aircraft include:

• the number of groups of horses and the number of horses in each group (a group can be a single horse if it is on its own)
• the distance from the centreline (inner edge) of the survey strip – the following categories are used – 0 to 20 m, 20 to 40 m, 40 to 70 m, 70 to 100 m and 100 to 150 m
• vegetation cover at point-of-detection (open or timbered)
• observer seating position.

The location of transects followed a systematic random sampling design – that is, the starting point for the transects in each survey block is randomly generated, and the transects then followed a systematic pattern. This means the sample was unbiased.

The sample of observations is then analysed using advanced software to estimate the wild horse population in the entire survey area.

It is rare that a count (or census) of an entire animal population can be undertaken in the wild, whether by air or ground.

The park's size and mix of rugged mountain escarpments, valleys and remote wilderness areas means it is impossible to count every wild horse in the landscape individually.

Instead, we use the internationally recognised best practice method to estimate the wild horse population. This method gives a 'confidence interval' – a range rather than a single number is more reflective of the true survey results.

Statisticians and scientists use a confidence interval to express how accurate an estimate is. A 95% confidence interval is used to provide a population estimate range. This approach accounts for the inherent uncertainty in sampling over such a large and variable landscape. Scientifically, a 95% confidence interval represents the range in which the true population size would lie in 95 out of 100 surveys. Practically, it gives a high level of confidence that the true population size lies within this range for the survey method used.

The next population survey is scheduled to occur before the end of 2026.