Editor’s note: in 2018 my trail camera caught a cougar drinking at the trough under the windmill so when The Horse Shelter just east of Cerrillos reported two foals were killed a few years ago nobody was very surprised. An Appaloosa mare that foaled in 2023 showed up without it several weeks later so the logical conclusion was that a cougar took it. She just delivered again and the local herd has doubled in size hooking up with another probably from the Kewa Pueblo.
DEAR WILD HORSE ADVOCATES: You can't have it both ways
One of the biggest contradictions in modern wild horse debates is hearing people insist that every family band must remain completely intact while also arguing that inbreeding is a major concern. Those positions are not fully compatible under basic population genetics.
Family bands are social structures, not genetic management units. Long-term genetic health depends on effective population size (Ne), breeding diversity, dispersal, and gene flow (Waples et al., 2013; Hoban et al., 2021). When populations become smaller, geographically restricted, or behaviourally closed, relatedness and homozygosity increase over time because the same lineages repeatedly breed within a limited population pool (Thompson et al., 2024).
Importantly, wild horses do not naturally remain in their natal bands forever. As horses reach sexual maturity, young stallions typically disperse from their birth bands, and some mares disperse as well (Linklater, 2013; Nuñez et al., 2016). This natal dispersal is a normal behavioural mechanism that promotes gene flow and reduces close inbreeding in free-ranging horse populations (Linklater, 2013). Preventing movement between groups or restricting populations into isolated management areas interferes with those natural dynamics.
In free-ranging horse populations, most foals do not remain permanently in their natal band once they reach sexual maturity. Both colts and fillies naturally disperse, although males usually leave earlier and more consistently than females. Dispersal is a well-documented behavioural mechanism that reduces inbreeding risk in equids (Feh, 1999; Berger, 1986).
There is no single universal percentage because dispersal rates vary by habitat, density, stallion turnover, and herd structure, but studies consistently show that the majority of offspring eventually leave their natal group. Feh (1999), studying semi-feral horses, reported that dominant stallions expelled approximately 82–84% of daughters, greatly reducing opportunities for sire-daughter breeding.
Actual sire-daughter breeding rates in naturally functioning herds are relatively low, but a consequence of restricting dispersal of family bands. Berger (1986) found that only about 3.9% of matings involved fathers and their genetic daughters in a free-ranging horse population. Feh (1999) later found somewhat higher rates (~10–11%) under certain conditions, particularly when normal dispersal patterns were disrupted or when horses had prior captive management histories.
These findings demonstrate that horse societies are dynamic, not static “family units,” and that natural dispersal behaviours play a major role in limiting close inbreeding. Corona, from Sand Wash Basin, has been observed exhibiting reproductive behaviour with his presumed daughters on numerous occasions, with observations suggesting the pairings may have produced a foal.
At the same time, many advocates oppose nearly all removals, the introduction of horses from outside, and the disruption of existing bands. But if populations remain closed with limited dispersal and limited external gene flow, close relatives will inevitably breed over time, particularly in smaller herds or fragmented habitats (Hoban et al., 2021; Thompson et al., 2024).
Modern conservation genetics, therefore, focuses on maintaining an adequate effective population size and preserving gene flow, not simply preserving every social grouping indefinitely (Frankham et al., 2017; Hoban et al., 2021). Social stability matters, but it cannot replace population genetics.
You cannot simultaneously argue that:
1. No horses should ever be removed,
2. Family bands must remain permanently intact,
3. Outside gene flow should be restricted or prevented,
4. There will be no increase in inbreeding risk.
Those arguments fundamentally conflict with established conservation genetics principles.
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References:
Berger, J. (1986). Wild horses of the Great Basin: Social competition and population size. University of Chicago Press.
Feh, C. (1999). Alliances and reproductive success in Camargue stallions. Animal Behaviour, 57(3), 705–713.
Feh, C., & Munkhtuya, B. (2008). Male infanticide and paternity analyses in a socially natural herd of Przewalski’s horses: Sexual selection? Behavioural Processes, 78(3), 335–339.
Frankham R, Ballou JD, Ralls K, et al. Genetic Management of Fragmented Animal and Plant Populations. Oxford University Press, 2017.
Hoban S, Bruford MW, Funk WC, et al. Global commitments to conserving and monitoring genetic diversity are now necessary and feasible. BioScience. 2021;71(9):964-976.
Linklater WL. Adaptive explanation in socio-ecology: lessons from the Equidae. Biological Reviews. 2013;88(1):182-198.
Nuñez CMI, Adelman JS, Mason C, Rubenstein DI. Immunocontraception decreases group fidelity in a feral horse population during the non-breeding season. Applied Animal Behaviour Science. 2016;183:13-17.
Rubenstein, D. I. (1986). Ecology and sociality in horses and zebras. In D. I. Rubenstein & R. W. Wrangham (Eds.), Ecological aspects of social evolution (pp. 282–302). Princeton University Press.
Thompson MA, McCann BE, Rhen T, Simmons R. Population genomics provide insight into ancestral relationships and diversity of the feral horses of Theodore Roosevelt National Park. Ecology and Evolution. 2024;14:e11197.
Waples RS, Luikart G, Faulkner JR, Tallmon DA. Simple life-history traits explain key effective population size ratios across diverse taxa. Proceedings of the Royal Society B. 2013;280:20131339.
Cresciente (dun) & Poseidon (black/dark bay)
Sand Wash Basin, Colorado, 2017