Populations of free-roaming horses can double in size about every four years and triple every six years:1
The same reproduction rate can be applied to the three or so small bands of horses that were in Placitas around 15 years ago, allowing us to see how a population of about 25 horses could grow to nearly 200 over ten years:
During the last decade or so, Placitas has also had additional horses arriving from pueblo lands and, judging by the presence of an occasional gelded or shod horse, some horses turned loose in the Placitas hills by owners during the economic downturn. All this led to a population expansion that quickly outstripped the land’s ability to provide forage.2
1 Using Science to Improve the BLM Wild Horse and Burro Program: A Way Forward. Committee to Review the Bureau of Land Management Wild Horse and Burro Management Program; Board on Agriculture and Natural Resources; Division on Earth and Life Studies; National Research Council. Washington, DC: National Academies Press, 2013, p. 56. Available here.
2 According to the Task Force on Free-Roaming Horses of Placitas, Final Report (Sandoval County and New Mexico First, 2014), informal counts of the horse population by residents in 2011-2013 resulted in estimates ranging from about 115 horses in the immediate Placitas vicinity to more than 550 horses in the broader Placitas and Algodones areas, with unknown numbers in Diamond Tail, Crest of Montezuma, Ball Ranch, and other areas. One Saturday in 2012, the editors of this blog counted more than 40 horses along a three-mile stretch of Camino de la Rosa Castilla in northeast Placitas and another 12 in the nearby Cedar Creek subdivision.