Aspen Bibliography

Population dynamics of feral horses in Western North America

Document Type

Article

Journal/Book Title/Conference

Journal of Equine Veterinary Science

Volume

6

Issue

5w

First Page

231

Last Page

235

Publication Date

1986

Abstract

A review of various studies on the population dynamics of feral horses (Equus caballus) in western North America reveals considerable variation both among and within individual herds, thereby rendering generalizations of questionable validity. In most populations, females commence reproduction at 3–4 years of age, with approximately one half of the mares in these age classses bearing foals in a given year. However, recent studies indicate that a modest but variable fraction (15–35%) of the 2-year olds in some populations may produces young. Among older age classes, fecundity rates generally range between 60% and 85%. Survival ratesamong foals and older animals probably average 90% and 95%, respectively, except in years of particularly adverse weather conditions (i.e. severe winters and drought). Although annual rates of increase of at least 20% have been documented in some herds, a more realistic average for most populations probably approximates 15%. Recent studies have demonstrated that population estimates based on aerial counts underestimate the actual number of animals present by a factor of 10–60%, depending upon the type of terrain and vegetation over which the census was flown.

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