Recognition of unfamiliar predators in domestic horses through only visual predator cues | PLOS One
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Abstract<br>Acoustic, olfactory, and visual predator cues trigger various adaptive responses among a variety of prey species even when they are under human protection since birth. Previous studies have found that domesticated animals show increased vigilance, stress, flight, and aggregation behaviors in response to predation threats. These investigations, however, did not directly test visual threatening cues alone in animals that communicate more with body language than vocalizations while considering individual temperament and social status. The current study aims to address this issue. Eighteen horses housed at the Ohio State University Equine Center with mixed age and sex were the subjects of the experiments (mean age = 7 years). The horses were shown affiliative and aggressive behaviors of a pack of wolves (unfamiliar predator) and grazing wombats (unfamiliar non-predator) on a projector without any acoustic cues while their reactions were recorded with an equine heart monitor and camera. Data were also collected on assessments of anxiety/fear, social dependency, and social status in the herd. Results showed that domestic horses distinguished an unfamiliar predator from an unfamiliar non‑predator based on visual cues alone, showing significantly higher heart rate (HR) responses to wolf videos than to wombat videos (P = 0.0022). HR also increased relative to baseline during wolf videos (P = 0.0005), whereas HR during wombat videos did not differ from baseline (P = 0.28). There were no significant differences in HR responses to affiliative vs. aggressive behaviors displayed by wolves (P = 0.4033). The age of the horses was negatively associated with fearfulness (P = 0.0048) and social dependency (P = 0.0076). Male horses showed a more heightened HR to unfamiliar predator cues compared to females (P = 0.0088). High social status was associated with an increased HR response to unfamiliar predator stimuli (P = 0.033) but was unrelated to control stimulus HR (P = 0.26), baseline HR (P = 0.32), fearfulness (P = 0.26), social dependency (P = 0.85), age (P = 0.42), and sex (P = 0.61). Lateralized gaze revealed a near total absence of left eye viewing across all stimuli, with no difference between right gaze and binocular look durations for wolves (P = 0.83). In contrast, horses showed a significant binocular preference over right-gaze when viewing wombats (P Citation: Hofacker R, Sebunia N, Pihlblad J, Benderlioglu Z (2026) Recognition of unfamiliar predators in domestic horses through only visual predator cues. PLoS One 21(7):<br>e0349298.
https://doi.org/10.1371/journal.pone.0349298<br>Editor: Laura Patterson Rosa, Long Island University - CW Post Campus: Long Island University, UNITED STATES OF AMERICA<br>Received: March 17, 2025; Accepted: April 28, 2026; Published: July 15, 2026<br>Copyright: © 2026 Hofacker et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.<br>Data Availability: All relevant data are deposited in the Dryad repository for open access at https://doi.org/10.5061/dryad.x3ffbg827.<br>Funding: The senior author (ZB) received a research development grant from the College of Arts and Sciences at The Ohio State University. The first author (RH) was supported for experimental expenses, and co‑authors (NS & JP) received stipend support from these funds. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. No additional external funding was received for this study.<br>Competing interests: The authors have declared that no competing interests exist.
Introduction<br>Domestic horses, Equus caballus, are prey animals that have long been under the protective care of humans since their domestication about 5,500 years ago [1,2]. Although their main natural predator, the grey wolf, Canis lupus has been reintroduced in North America and Europe [3], domestic horses are currently under little to no predation threat and are unlikely to encounter wolves while in human care.
Adaptive behaviors in response to predators in horses and most prey species appear to remain intact, however. For example, domesticated cattle and sheep show increased vigilance, flight, and aggregation behaviors in response to predation threats [4,5]. Similarly, domestic horses distinguish between threatening and non-threatening auditory cues and natural vs. unfamiliar predator vocalizations by showing increased alertness and defensive herd formations when threatened [1]. In...