Counting horses

How many are there? It is a common and important question in controversies about wildlife. Knowing the number of animals is the first step to finding out whether a population is declining or increasing, and if there are too many or not enough.

Rust band – Kaimanawa wild horses – looking across Argo Basin towards Auahitotara Peak (zone 28, circa 1994-98).

Both sides of the debate about horse populations – those who want them on the landscape and those that do not – need an answer to the population size question. Knowing how many horses there are is also, of course, an essential guide to deciding how to manage any population and evaluating whether management achieved its objectives. Unsurprisingly therefore, estimates of horse population size are inevitably contentious and contested.

Unfortunately, estimating population size is a universal challenge. It is difficult to do well for most species. Many animals are difficult to count because they are hard to see. They might be small, and live in treed landscapes, in caves, or underground. They might hide when startled, or be camouflaged against the background.

But counting horses should be comparatively easy – right? They are large and live in small groups whose members one could mostly count on the fingers of two hands – only occasionally also requiring your toes. They also prefer to roam open, grassed landscapes. Being large, group-living and on grasslands makes them easy to see. Only rarely do they seek shelter that might hide them. When they do it is usually when the weather is poor and no reasonable person wants to be counting horses anyway. Sure, tall trees and shrubs might obscure some of the population most of the time but generally horses should be easy to find and count in fair weather. All this is true, but horses are difficult to count because they pose a less commonly encountered challenge – they run.

Barbourofelis, a sabre-tooth cat, ambushes a three-toed Hipparion, relative of the modern horse. Source: Carl Buell

The blame for our difficulties counting horses can probably be placed with their ancient predators – most of which are now extinct. Some were large, ‘sit and wait’ or ‘ambush’ predators. Some were smaller but fast pursuit predators hunting in packs. Horses, therefore, have an extraordinary jump and acceleration from standing. In the world that horses evolved, so the hypothesis (story) goes, there were the ‘quick and the dead’.

Paul Kane painting depicting horseback hunting of buffalo (circa 1851-1856).

Of course, this will be no surprise to the equestrian. Powerful hind-leg muscles deliver a horse’s maximum speed within three seconds. Key to acceleration is the leap into the first stride – hence also the horses remarkable capacity to jump fences. The world record jump is almost two and a half meters (8 feet). Speed and the stamina to maintain it are also extraordinary in horses. They are fantastic runners. Speeds in excess of 50 km per hour (~30 miles per hour) are typical for the first kilometer or two and top-speeds of almost 90 km per hour (~55 miles per hour) are possible over shorter distances. Eighty kilometers can be achieved in just over four hours [1] – incredible endurance. It is not surprising that horse-racing and hunting from horseback have been a part of all cultures that domesticated the horse. The athleticism of the horse is exhilarating and inspiring – stirring many of us deeply, emotionally.

Being group-living animals, if one individual starts running the others will follow.  Even if you have no sense of the danger, if one of your group startles you had better run with them just in case. And if one group starts running, other near groups will also follow – fear is contagious. Running groups of horses merge and separate in a melee of groups forming larger groups and breaking apart again as they cross the broken landscape, sometimes at breakneck speed turning and twisting with the ridges, valleys and bluffs. We have documented what a serious challenge horse escape behavior can be to reliable estimates of population size [2].

Helicopter mustering on Stone Cabin Herd Management Area. Source: Laura Leigh

Horses are chased for muster the world over. Many have experience of being pursued by low-flying helicopters, motorcycles, and people on horseback. This experience adds to the contagion – they often fear us, and our steeds and machines. Given the large areas over which most horse populations roam, counting wild horses is most often conducted from a helicopter. How one avoids under- or over-counting horses in the melee which might result is critical to getting a useful estimate of population size.

Modern counting methods address the challenges of counting horses by sampling repeatedly from the same population and using techniques less likely to disturb the horses as they are counted. Unfortunately, some organisations continue to use flawed techniques – flawed because they attempt to census the population and do not address problems of under- and over-counting.

Understanding the strengths and limitations of different population estimates is important to contributing strongly and constructively to debates about horse population size. Knowledge is power. In controversies about wild horses, often between government and community groups, it is most often the government that generates estimates of horse population size. Community groups are less likely to have the expertise to challenge official assertions about population size and trends. In future posts I will consider the scientific techniques for estimating horse population size, and evaluate their strengths and limitations. I’d like to redress the knowledge imbalance.

Bibliography

1. Budiansky, S. 1997. The Nature of Horses – Exploring Equine Evolution, Intelligence, and Behavior. The Free Press, New York. 290 pp.

2. Linklater, W.L. & Cameron, E.Z. 2002. Escape behaviour of feral horses during a helicopter count. Wildlife Research, 29: 221-224.

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