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PloS one2026; 21(7); e0349298; doi: 10.1371/journal.pone.0349298

Recognition of unfamiliar predators in domestic horses through only visual predator cues.

Abstract: 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 < 0.0001). These results demonstrate that, based on visual cues alone, horses exhibit physiological alertness toward potential predatory threats while responding to non-threatening stimuli with exploratory gaze behaviors.
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.
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Publication Date: 2026-07-15 PubMed ID: 42455789PubMed Central: PMC13372171DOI: 10.1371/journal.pone.0349298Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study investigated whether domestic horses, which rely heavily on body language for communication, can recognize unfamiliar predators based solely on visual cues without any accompanying sounds or smells.
  • The research involved showing horses videos of wolves (predators) and wombats (non-predators) to assess their physiological and behavioral responses.

Purpose and Background

  • Previous research has shown that many prey animals respond adaptively to predator cues such as sounds, smells, and visuals, even if they have never encountered predators directly.
  • Domestic animals raised around humans from birth typically display increased vigilance, stress, and social behaviors when exposed to predator threats.
  • Most prior studies combined multiple types of predator cues or focused on animals that communicate largely via vocalizations.
  • This study specifically focused on visual predator cues alone, considering horses’ reliance on body language rather than vocalization, and also evaluated how individual traits like temperament and social rank affect responses.

Methods

  • Subjects: 18 domestic horses of varying ages and sexes housed at Ohio State University Equine Center (mean age about 7 years).
  • Visual stimuli: videos depicting either a pack of wolves showing affiliative or aggressive behaviors (unfamiliar predators) or grazing wombats (unfamiliar non-predators) were shown on a projector.
  • No acoustic (sound) cues were used to isolate the effect of visual cues.
  • Data collected included:
    • Heart rate (using an equine heart monitor) as a measure of physiological arousal.
    • Behavioral responses recorded via video camera.
    • Assessments of horses’ anxiety/fearfulness, social dependency, and social status within the herd.
    • Lateralized gaze analysis to determine eye preference when viewing stimuli.

Key Findings

  • Horses distinguished visually between an unfamiliar predator (wolves) and an unfamiliar non-predator (wombats) based solely on visual information:
    • Heart rate was significantly elevated when watching wolf videos compared to wombat videos (P = 0.0022).
    • Heart rate increased relative to baseline during wolf videos (P = 0.0005) but not during wombat videos (P = 0.28), indicating heightened physiological alertness only to predator cues.
  • Heart rate did not differ significantly between viewing affiliative versus aggressive wolf behaviors (P = 0.4033), suggesting horses respond to predator presence regardless of specific wolf behavior.
  • Individual factors influencing responses:
    • Older horses showed less fearfulness and social dependency (negative associations with age, P = 0.0048 and 0.0076 respectively).
    • Male horses exhibited stronger heart rate responses to predator cues than females (P = 0.0088).
    • Horses with higher social status had larger heart rate responses to predator stimuli (P = 0.033), but social rank did not correlate with baseline heart rate or fearfulness.
  • Lateralized gaze patterns:
    • Left eye use was almost absent when viewing all stimuli.
    • For wolf stimuli, horses showed no significant difference between right eye and binocular viewing durations.
    • For wombat stimuli, horses preferred binocular vision significantly more than right-eye viewing (P < 0.0001), indicating exploratory behavior toward non-threatening cues.

Conclusions and Implications

  • Domestic horses are capable of visually recognizing unfamiliar predators and showing physiological signs of alertness, even without additional sensory cues like sound or smell.
  • Their ability to discriminate predator vs. non-predator stimuli visually highlights the importance of vision in predator recognition, especially relevant for species like horses that rely on body language for communication.
  • Individual differences such as age, sex, and social rank modulate the horses’ physiological sensitivity to predator cues.
  • Lateral gaze findings suggest horses use different visual strategies depending on the threat level of the stimulus, with binocular vision linked to investigation of neutral stimuli and right gaze associated with predator alertness.
  • Understanding how domestic animals assess threats visually can improve welfare and management practices by identifying stressors and helping design environments that minimize undue anxiety.

Cite This Article

APA
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), e0349298. https://doi.org/10.1371/journal.pone.0349298

Publication

PloS one
ISSN: 1932-6203
NlmUniqueID: 101285081
Country: United States
Language: English
Volume: 21
Issue: 7
Pages: e0349298
PII: e0349298

Researcher Affiliations

Hofacker, Rachel
  • Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus Ohio, United States of America.
  • Current Affiliation: College of Veterinary Medicine, Ohio State University, Columbus Ohio, United States of America.
Sebunia, Natalie
  • Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus Ohio, United States of America.
  • Current Affiliation: Cornell University, College of Veterinary Medicine, Ithaca New York, United States of America.
Pihlblad, Jessica
  • Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus Ohio, United States of America.
  • Current Affiliation: College of Veterinary Medicine, The University of Arizona, Tucson, Arizona, United States of America.
Benderlioglu, Zeynep
  • Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus Ohio, United States of America.

MeSH Terms

  • Animals
  • Horses / physiology
  • Predatory Behavior / physiology
  • Female
  • Male
  • Cues
  • Heart Rate / physiology
  • Fear
  • Wolves / physiology
  • Behavior, Animal / physiology
  • Aggression

Conflict of Interest Statement

The authors have declared that no competing interests exist.

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