Great Basin Naturalist


A population of feral horses (Equus caballus) in the southern Great Basin Desert of Nevada was monitored from 1989 to 1998 to determine size, distribution, and population trends. All individual horses observed in the population were identified by unique markings during the first 2 yr of study, and most animals could be observed annually. During this study no new horses were identified in the population, indicating that no immigration occurred from outside populations. The population reached a high of 65 horses yearling or older in 1992 and declined each year thereafter, reaching a low of 36 horses in 1998. Estimated foal survival averaged <12% over 8 yr. Only 11 horses were recruited into the population as yearlings or older animals during the study. Mountain lion predation is hypothesized as a major factor limiting growth of this feral horse population.