- Content Type: Book Chapter
The Changes In The Herd
A note on what this is.
The articles in this work are written to be felt. This page is written to be checked. It is the room where the studies behind the herd pieces are kept — what each one actually did, what it actually found, and what that finding lets us see. If something in an article made you want to know how we know it, this is where to look. And if you teach this material to others, this is the ground you can stand on when someone asks you to defend it.
One honest thing first. Almost all of this evidence comes from feral and wild horses — the Kaimanawa ranges of New Zealand, the hills of Serra d'Arga in Portugal — horses living more or less on their own terms. That is both its strength and its limit. These studies cannot tell us directly how the horses in our barns and paddocks ought to be kept. What they can tell us is what horses do when they are free to choose — which is exactly the baseline we need before we start making the choices for them. Read them that way: not as instructions, but as a picture of the thing we are working with.
Each study below is paraphrased in plain language, with the full citation so you can go to the source yourself.
The stallion is not the engine of the herd
Linklater, W. L., & Cameron, E. Z. (2000). Tests for cooperative behaviour between stallions. Animal Behaviour, 60(6), 731–743.
In the Kaimanawa ranges, the researchers compared nine bands held by more than one stallion against eighteen held by a single stallion. The question behind it was whether extra stallions help — whether they cooperate to hold and defend a larger or stronger group of mares. They don't. The number of stallions in a band had no positive effect on the size of the mare group, on how stable it was, on the quality of the range it used, or on how successfully it bred. Bands with several stallions were no better off, and the relationships between those stallions were marked far more by conflict than by cooperation.
What it lets us see: if the stallion were the thing holding the herd together, more of him should mean more herd. It doesn't. Whatever does the holding, it is not the stallion's defence of the group.
Harassment has a cost — and some mares move
Linklater, W. L., Cameron, E. Z., Minot, E. O., & Stafford, K. J. (1999). Stallion harassment and the mating system of horses. Animal Behaviour, 58(2), 295–306.
The same population, seen from the mares' side. The researchers compared mares living in single-stallion bands, mares in multistallion bands, and mares who belonged to no fixed band at all — the ones they called social dispersers, or maverick mares. Across a range of measures — how far the mares had to travel, their parasite loads, their body condition, how many foals they raised and how many survived — the mares in multistallion bands and the maverick mares came off worse. The researchers tied this to harassment: the pursuing, driving, and pressing a mare undergoes, and what it costs her when there is more of it.
What it lets us see: a mare's place in the social structure shows up in her body and in her foals. It also names something we tend to overlook — that mares are not fixed possessions of a band. Some stay; some travel.
Friendship between mares is load-bearing
Cameron, E. Z., Setsaas, T. H., & Linklater, W. L. (2009). Social bonds between unrelated females increase reproductive success in feral horses. Proceedings of the National Academy of Sciences, 106(33), 13850–13853.
This is the study that turns the picture over. Working again with the feral mares, the researchers measured how strongly each mare was bonded to other mares, and set that against how successfully she bred. Mares with stronger bonds raised more foals. And these were bonds between unrelated mares — so this was not kin helping kin, the explanation that muddies most primate studies of the same question. It was friendship, built on familiarity and chosen company, and it paid off partly by reducing the harassment a mare endured. The bonds themselves were strong and lasting, and built around preferred partners.
What it lets us see: the friendships are not a pleasant extra laid over the real structure of the herd. They are the structure — measurable in the hardest currency there is, the foals a mare raises. And they are made of familiarity and choosing, not blood.
There is no single shape — equid society is layered
Maeda, T., Ochi, S., Ringhofer, M., Sosa, S., Sueur, C., Hirata, S., & Yamamoto, S. (2021). Aerial drone observations identified a multilevel society in feral horses. Scientific Reports, 11, 71.
A different population entirely — the feral horses of Serra d'Arga in Portugal — and a different method. The researchers flew drones overhead at regular intervals, recorded the exact position of every horse, and used the distances between them to map who kept company with whom. Two things came out of it. First, the horses fell into small "units" — family groups that genuinely held together. Second, those units did not scatter at random; they associated with one another to form a larger "herd," and within that herd the big mixed-sex family groups tended to hold the center while the all-male bachelor groups stayed out toward the edges. A society with more than one level to it.
What it lets us see: the herd is not one thing with one correct shape. The family band, the lone and bachelor males, the larger gathering they all belong to — these are not exceptions to a rule, they are the structure. And because this turned up in Portugal while the bonding and harassment work was done in New Zealand, it is not the quirk of a single place.
The groundwork: how a wild population is actually arranged
Linklater, W. L., Cameron, E. Z., Stafford, K. J., & Veltman, C. J. (2000). Social and spatial structure and range use by Kaimanawa wild horses (Equus caballus: Equidae). New Zealand Journal of Ecology, 24, 139–152.
Underneath the more pointed studies sits the patient descriptive work: who lived with whom, where they ranged, how the bands and the wider population were laid out across the land. It is less dramatic than the others and more important than it looks — it is the map the other findings are placed on. A great deal of the New Zealand horse work shares this ground, which is worth holding in mind: much of what we know in fine detail comes from this one, unusually well-studied population.
What it lets us see: the baseline picture — what a horse society looks like when it is laid out across real country and watched closely over time. Everything else is read against this.
This room will grow. As the herd work goes on — into how horses bond, how groups change, and what happens when we are the ones deciding who lives with whom — the studies that ground each new piece will be added here, in the same plain form: what was done, what was found, and what it lets us see. It is meant to be one honest place to stand, for anyone who wants to know how we know.