Proximate factors affecting mortality and maternal abandonment of young free-roaming feral horse foals

The burgeoning population of feral horses in the American west is due to high population growth, resulting from low adult mortality and high foal survival. In two populations of feral horses in western Utah, USA only 15 foals died (5%; mean age < 1 month) over a 4-year period. Seven additional foals (age < 70 days) were observed separated from their dam, with no return to suckling or associating with the dam (i.e., abandoned). Factors affecting fate of foals were examined by comparing dead and separated foals with siblings (n = 19 dams, n = 32 siblings). Foals becoming separated or dying were observed in all years of the study, were unrelated to horse density, environmental effects, or gather events. There was no effect of dam body condition, parity, or age on foal survival or separation, and no effect of length of time the dam was in a group, whether the foal was born into the same group as conceived, and number of group changes made by the dam while pregnant. Dams of foals that died or were separated were more likely to change groups within 2 months after the foal was first seen, mostly after foal death or separation. Separated foals were near their dam less often, but there was no difference in frequency of social interactions. Separation of foals and dams is a natural occurrence in feral horses and survival likelihood for these foals is high - all separated foals that remained on the range in this study survived. (c) 2023 The US Geological Survey and Elsevier Inc. All rights reserved.